Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Acoustic Performance-Based Design: A Brief Overview of the Opportunities and Limits in Current Practice

Acoustic Performance-Based Design: A Brief Overview of the Opportunities and Limits in Current... acoustics Review Acoustic Performance-Based Design: A Brief Overview of the Opportunities and Limits in Current Practice Elena Badino * , Louena Shtrepi and Arianna Astolfi Department of Energy, Politecnico di Torino, 10129 Torino, Italy; louena.shtrepi@polito.it (L.S.); arianna.astolfi@polito.it (A.A.) * Correspondence: elena.badino@polito.it Received: 4 April 2020; Accepted: 26 April 2020; Published: 1 May 2020 Abstract: Current development in digital design, combined with the growing awareness of the importance of building performance, had drawn attention to performance-based design (PBD) in architecture. PBD benefits both design workflow and outcome, allowing one to control the performance of the design proposal since early design phases. The paper aims to explore its current application in the acoustic field, where its potential is still little exploited in architectural practice. A set of built case studies is collected and briefly analyzed with the aim to shed some light on the state of the art of the application of acoustic performance-based design (APBD) in practice. The analysis suggests that in order to encourage the application of APBD it is needed on one side to enhance the integration and interoperability among modeling and simulation tools, and on the other side to improve the acoustic knowledge and programming skills of the architectural practitioners. Keywords: performance-based design; acoustic design; digital workflow; architectural design; design optimization; form-finding 1. Introduction 1.1. Performance-Based Design Architectural problems generally combine a great multitude of objectives, which pertain to di erent fields, such as cultural, aesthetic, economic, structural and energetic ones. As these objectives often contrast with each other, it is crucial for the design team to find the most favorable solution in overall terms. According to the classification proposed by Shi [1], architectural objectives can be divided into three categories: structural performance, performance of the physical environment—both of which can be quantified—and aesthetic and cultural performance, which relates to unquantifiable aspects. Digital simulations and measurements on scale-models allow for the evaluation of the quantifiable performances of the design proposals prior to their construction. In common practice, such tools are generally used in late design phases to verify the adherence to the performance requirements prescribed in codes, standards and laws, and evaluate the need for late design adjustments [2–4]. However, in the recent years, another approach has gained popularity, according to which performance simulations are used to drive the design process. This approach is known as performance-based design (PBD): pertinent information on one or more performance aspects is gathered since early design phases, and the proposals are iteratively optimized based on the performance feedbacks. The design process follows the loop of generation–evaluation–modification, until a solution that meets the performance goal is achieved. While not discouraging the inclusion of unquantifiable goals and Acoustics 2020, 2, 246–278; doi:10.3390/acoustics2020016 www.mdpi.com/journal/acoustics Acoustics 2020, 2 247 aesthetical considerations, pertinent information on quantifiable performances can greatly support decision-making processes in the conceptual design stages. In early design phases, designers consider a wide range of possible design solutions. Design decisions made at this stage have the greatest impact on the final performances, while late-time design adjustments can rarely compensate poor decisions made in early stages [5–8]. Moreover, design modification taken in early design phases is less costly to implement than those taken in subsequent phases [4,9]. Therefore, PBD approach benefits both design workflow and final outcome, combining a decrease in cost and time, and enhances design quality [10–12]. Indeed, with PBD designers have a greater control over the performances since early design phases and, as a result, the need for late-time design modifications or “a posteriori” measures is prevented, enhancing the overall eciency of the design process. The PBD approach emerged in the l970s and has become increasingly more appealing to architects due to the technological advancement and, in particular, to the development of performance simulation and parametric modeling tools [1,13–16]. Some educational experiences, such as those in [16,17], suggest that architectural students are increasingly being encouraged to use these tools and include performance feedback to support design decisions during the early-stage design exploration. PBD marks the paradigm shift from the traditional “form-making” to the “form-finding” approach [18]. It allows one to displace traditional know-how, enabling designers to understand the e ects of di erent design features of the proposal on performance, and to identify design scenarios that best fulfill the unique requirements of each project. The PBD method can be subdivided into two subclasses according to the way the design optimization process is conducted. In “formation models” the modifications are applied manually by the operator, while in “generative models” the design proposals are directly optimized by the computer [19]. The latter subclass is also known as “performance-driven design” [1]. Following the manual procedure, the designers control the form-generation process, allowing for the introduction of unquantifiable criteria and the technical expertise of the operator. For instance, based on performance simulation feedbacks and technical knowledge, the operator generates new design alternatives and tests them until a satisfying solution is achieved. The generation of design proposals can be eased by the use of parametric modeling tools, such as Grasshopper [20] for Rhinoceros [21] and GenerativeComponents [22]. These tools allow one to define complex geometries and to easily modify them by controlling their parameters, thus preventing the need for the operator to manually redraw each design iteration. Adequate technical skills are required in manual processes, since the success of the optimization greatly relies on the correct understanding of the relations between design features and performance [2]. However, the time and manpower required in the processes may limit the number of iterations pursued and the e ectiveness of the design optimization [1,23]. On the other hand, generative models allow one to explore a wide number of design options with a limited involvement of the operator, exploiting the functionalities of optimization tools (e.g., Galapagos [24] and Octopus [25]) [1,2,18,26]. These tools, when paired to a parametric model and a performance simulation tool, allow one to automate the search of the most performing solution within the variation space defined by the operator, while also narrowing the space of possible solutions based on the estimated performance [27]. The population of candidate solutions evolves over many generations, until a satisfactory solution is reached. This enables one to explore a wide solution space and to find potentially unconsidered design options to address the specific requirements of the project [3,28]. In automated processes it is also possible to e ectively combine di erent performance goals in multiobjective optimization procedures, which can hardly be implemented manually. In automated procedures, the involvement of the designer is generally limited to the definition of the target performance objectives and of the boundaries of the variation space within which the generative process operates, which may reflect quantifiable and unquantifiable criteria [11]. Despite these advantages, manual procedures may be preferred by professionals to allow the design exploration to be guided by their intuition and expertise gathered by working in the field. Acoustics 2020, 2 248 Manual and automated procedures are often combined in di erent ways in hybrid methods, allowing one to exploit the advantages of both approaches, based on the requirements of the design process. The PBD approach enhances the eciency of the design process by enabling to optimize the architectural proposal with respect to the performance analyzed. However, the application of PBD method is still relatively limited currently. Indeed, current architectural practice often relies on experience-based know-how and performance simulations are mainly introduced in late design phases with the aim to verify the adherence to the performance requirements. 1.2. Performance-Based Design in Acoustics The implementation of PBD in the architectural acoustics field would allow the designer to better combine acoustic performance objectives with architectural goals. Architectural design and acoustic performances are strictly linked: the emitted sound is altered by the architectural space within which it is deployed, due to sound reflection, absorption and di usion phenomena occurring over its surfaces. In common practice, however, acoustic concerns are mainly restricted to the design of spaces intended for artistic performances, such as music venues and theatres. In such spaces, the architectural environment is meant to support the sound generated by the artists, and acoustic design is critical for both audience and performers [12]. However, as the benefits of acoustic comfort on the well-being of the population are being acknowledged, acoustics concerns are introduced in a wider variety of design problems [29]. Indeed, acoustic requirements are being increasingly extended to the design of spaces not related to artistic performances, such as classrooms, workplaces and urban environments, where an appropriate acoustic performance would benefit the hosted activities and the well-being of the users [29–32]. The acoustic performances of architectural spaces can be described by a number of parameters (e.g., sound pressure level, sound strength, reverberation time, clarity, etc.), each accounting for di erent perceptual aspects [33,34]. The acoustic requirements vary in accordance with the function hosted in the space. For instance, in spaces intended for speech, as classrooms and conference rooms, early sound reflections need to be adequately controlled to ensure the speech intelligibility [35]. In music venues, i.e., concert halls, opera houses, theatres and open-theatres, a number of parameters are usually considered to account for di erent perceptual aspects [36]. The proper management of early and late reflections is crucial, and it is generally obtained by opportunely treating the ambient with reflective and di usive surfaces. Di erently, the acoustic performance of sound reproduction rooms, like home theatres and recording studios, should be neutral, to prevent the space to alter the perception of recorded sounds; in this case a combination of sound di using and sound absorbing surfaces is preferred [37]. Currently, di erent commercial acoustic simulation tools are available (e.g., Odeon [38], CATT-Acoustic [39], Pachyderm Acoustics [40], etc.), allowing professionals to estimate the performance of design proposals using the geometrical acoustic method. The acoustic performance of a given environment is predicted based on its geometrical features and the acoustic properties of the materials applied to the surfaces. Normally, the acoustic analysis is run in an external application from the modeling environment, and a specific virtual model need to be prepared (e.g., geometrical simplification, surfaces divided into layers based on material and specific format) in order to be fed to the acoustic simulation tool. Besides geometrical acoustic simulations, some more sophisticated simulation methods, such as wave-based ones, have been applied to concert halls and other bigger environments [41–43]. However, these methods still require long simulation time and are not currently supported in any commercial acoustic simulation tool. Although architectural design should pursue aesthetical quality in parallel with acoustic performance objectives, the process of conciliating acoustic requirements and architectural quality is often dicult and time-consuming, given the di erent design approaches and criteria of the two disciplines [44,45]. In most cases, the architectural and acoustic specialists work rather independently, Acoustics 2020, 2 249 with relatively few exchanges between them [28,46]. For instance, the most common approach followed in the design of concert halls relies on well-known typologies (e.g., shoe-box, fan-shaped, vineyard, etc.) and integrates acoustic simulations in late phases of the design process to verify the adherence of the project to performative requirements. In the design of spaces intended for other purposes, acoustic performances are often overlooked, recurring to acoustic treatments to adjust the performances only in late design phases or after the construction. Since the projects at the final stages are already defined, normally, major form-modifications cannot be pursued anymore, and improvements can only be obtained by altering minor design features, resulting often in costly and little e ective solutions [5,6,47,48]. In this frame, the implementation of the PBD method in the acoustic field, known as acoustic performance-based design (APBD), would be able to overcome some of the main drawbacks of the traditional method and set-up an e ective collaboration between architectural and acoustic specialists. The feedback of the simulations enables one to identify the dependencies between the design features and the acoustic performance, and to optimize the project accordingly. However, despite the mentioned advantages, the application of APBD in current architectural practice appears to be limited. 1.3. Objectives The aim of this paper is to provide an overview of the state of the art of the application of the acoustic performance-based design method through the gathering of a set of built case studies. The design procedures followed in the development of the case studies are briefly described, to highlight the benefits of the application of APBD and suggest possible improvements to extend its application. 2. Research Methods This paper presents and investigates a set of 19 built case studies developed with APBD, which were gathered through a literature research. The methodology followed in this work is similar to that applied in review studies pertaining to the architectural field, as in [49]. For this work, unbuilt examples, as well as examples built as scaled prototypes or which lacked adequate documentation, were excluded from the analysis. The research is limited to the publicly available information on the built case studies, which was mainly gathered from journal articles, conference proceedings, books and web articles. Therefore, the presented collection cannot be considered comprehensive, as it excludes the projects, which are not documented in literature, as it is often the case of projects developed by professionals. Moreover, it must be highlighted that, with the exception of case studies developed for research purposes, the publicly released information regarding the design workflow and the performance parameters considered in the optimization process is generally rather limited. Despite these limitations, the presented collection will be hopefully meaningful and will help to delineate the state of the art of the APBD method, by briefly describing the design outcomes, as well as the design processes and the strategies followed to enhance their performances. 2.1. Selection of Case Studies The research was conducted on the literature available on online databases as Scopus [50] and ResearchGate [51], on Google search, and in the academic libraries of Politecnico di Torino. Although scientific literature has been privileged, the support of Google search engine was exploited to extend the collection of case studies and to find further information. It must be noted that, for certain projects, further details were asked to the professionals involved in the projects via personal communications. Common keywords used in the search enquiries to filter results were: “performance-based design”, “form-finding”, “performative design”, “performance”, “architecture”, “design”, “generative”, “optimization”, “simulation”, “acoustics” and “sound”. Only built examples with adequate documentation were selected for the analysis. Acoustics 2020, 2 250 According to these criteria, 19 built examples were collected. In the following section, the case studies were briefly described and information on the design method and the tools used were gathered. 2.2. Case Studies The 19 case studies, which were briefly described in the following sections, were clustered according to their primary purpose and architectural characteristics. The first section, named “music venues” (Section 2.2.1) collected the projects that were designed to support of music and other artistic performances (i.e., concert halls, acoustic shells, etc.), while the second section, named “other spaces” (Section 2.2.2), gathered projects that were meant to host other functions or were developed as artistic installations. 2.2.1. Music Venues The Philharmonie de Paris Design: Ateliers Jean Nouvel, Brigitte Métra Associés; Acoustics: Marshall Day Acoustics, Nagata Acoustics, Studio DAP, Kahle Acoustics, Altia Acoustique, Jean-Paul Lamoureux and ASC; Paris, France, 2015 The project is the winning proposal of an international competition for the Philharmonie de Paris, whose main venue is a 2400 seats concert hall primary used for orchestral acoustic music performances (Figure 1). The acoustic brief for the “Grande Salle” explicitly called for an innovative shape for the concert hall with a limited distance between stage and seats, optimization of both early and late acoustic responses and also defined more than 10 acoustic requirements to be met (sound strength, reverberation time, clarity, etc.). The acoustic design started with the study of the sound reflections through laser measurements in scale models and continued with the support of parametric modeling and acoustic simulation tools, using Grasshopper, Maya [52] and Odeon. The solution adopted is made of two nested chambers that balance early and late reflections: the inner provides acoustical clarity and visual intimacy; the outer provides high reverberation, with an overall volume of 37,700 m . The inner chamber is characterized by the presence of suspended reflectors, called “nuages”, along with the balconies’ fronts and walls, namely “ribbons”, which provide early sound reflections. The design of the “nuages” and “ribbons” was developed though the APBD method, following an iterative form-optimization process guided by the relations between their geometry and the acoustic performance at the audience positions. Initially, the form optimization process was carried out manually, while in subsequent phases it was pursued with the aid of automated processes using Grasshopper and Maya. The “nuages” and “ribbons” have been optimized to provide the desirable amount of early sound reflection over the audience in order to meet the acoustic requirements, such as time delay and level di erence between direct and reflected sound, while also considering architectural and theatrical requirements. Odeon simulations were used after the optimization procedure to further verify the design outcome. Such simulations evidenced that the optimization process lead to significant performance improvements without compromising the architectural concept [53–59]. Acoustics 2020, 2 251 Acoustics 2020, 3 FOR PEER REVIEW 6 Figure 1. Philharmonie de Paris. Image courtesy © William Beaucardet. Figure 1. Philharmonie de Paris. Image courtesy © William Beaucardet. Elbphilharmonie Concert Hall 2.2.1.2. Elbphilharmonie Concert Hall Design: Herzog and de Meuron, Acoustics: Nagata Acoustics; Hamburg, Germany, 2017 The design of the main concert hall of the Elbphilharmonie, the “Grosser Saal” (Figure 2), is based Design: Herzog and de Meuron, Acoustics: Nagata Acoustics; Hamburg, Germany, 2017 on the vineyard configuration and features 2100 seats and a volume of 23,000 m . The APBD approach The design of the main concert hall of the Elbphilharmonie, the “Grosser Saal” (Figure 2), is informed the design of the 10,000 unique acoustic di usive panels that line the ceiling, walls and based on the vineyard configuration and features 2100 seats and a volume of 23,000 m . The APBD balustrades of the venue, whose engraved pattern has been defined through a generative design approach informed the design of the 10,000 unique acoustic diffusive panels that line the ceiling, process. The development of the project involved the use of an acoustic simulation tool, parametric walls and balustrades of the venue, whose engraved pattern has been defined through a generative modeling and optimization systems. Moreover, a 1:10 scale model was also used to test the ecacy design process. The development of the project involved the use of an acoustic simulation tool, of the customized di using panels in eliminating long path echoes. Each group of seating of the parametric modeling and optimization systems. Moreover, a 1:10 scale model was also used to test audience is served by unique gypsum fiberboard panels, to create a balanced reverberation across the efficacy of the customized diffusing panels in eliminating long path echoes. Each group of seating the entire hall. Their design, which is the result of a close collaboration between acousticians and of the audience is served by unique gypsum fiberboard panels, to create a balanced reverberation architectural designers, combines acoustic performance and aesthetics through an irregular pattern of across the entire hall. Their design, which is the result of a close collaboration between acousticians “seashell” cells engraved in their surfaces. The APBD method has been followed in the design of the and architectural designers, combines acoustic performance and aesthetics through an irregular “seashell” pattern, which is optimized to di use sound waves over the seating of the audience and pattern of “seashell” cells engraved in their surfaces. The APBD method has been followed in the to eliminate detrimental echoes. The cells of the pattern feature a width ranging from 40 to 160 mm, design of the “seashell” pattern, which is optimized to diffuse sound waves over the seating of the and a depth ranging from 10 to 90 mm. In particular, in locations where it was required to eliminate audience and to eliminate detrimental echoes. The cells of the pattern feature a width ranging from echoes, the sound scattering performance of the panels were enhanced by the greater depth of the 40 to 160 mm, and a depth ranging from 10 to 90 mm. In particular, in locations where it was required engraved cells, which measures 50–90 mm, while when soft reflections are desired, the cells feature to eliminate echoes, the sound scattering performance of the panels were enhanced by the greater a depth in the range of 10–30 mm. The generation of the pattern of the panels was performed by a depth of the engraved cells, which measures 50–90 mm, while when soft reflections are desired, the custom algorithm, able to define a unique solution for each panel to meet the acoustic requirements. cells feature a depth in the range of 10–30 mm. The generation of the pattern of the panels was In addition to acoustic simulations, also scale model measurements were used to verify the results of performed by a custom algorithm, able to define a unique solution for each panel to meet the acoustic the simulation and ensure the e ectiveness of the pattern in echoes suppression [60–64]. requirements. In addition to acoustic simulations, also scale model measurements were used to verify the results of the simulation and ensure the effectiveness of the pattern in echoes suppression [60– 64]. Acoustics 2020, 2 252 Acoustics 2020, 3 FOR PEER REVIEW 7 Figure 2. The “Grosser Saal” of the Elbphilharmonie. Image courtesy © Maxim Schulz. Figure 2. The “Grosser Saal” of the Elbphilharmonie. Image courtesy © Maxim Schulz. Anneliese Brost Musikforum Ruhr 2.2.1.3. Anneliese Brost Musikforum Ruhr Design: Bez + Kock Architekten; Acoustics: Kahle Acoustics, Müller-BBM; Bochum, Germany, 2016 The project is the winning proposal of the design competition for the concert hall for the Bochum Design: Bez + Kock Architekten; Acoustics: Kahle Acoustics, Müller-BBM; Bochum, Germany, 2016 Symphony Orchestra, which called for a shoe-box venue with a volume of 14,000 m , visual intimacy and The project is the winning proposal of the design competition for the concert hall for the Bochum less than 1000 seats. The concert hall developed by Bez + Kock Architekten conciliates these conflicting Symphony Orchestra, which called for a shoe-box venue with a volume of 14,000 m , visual intimacy goals by locating almost 1/3 of the required volume above the sound-transparent grid-ceiling (Figure 3). and less than 1000 seats. The concert hall developed by Bez + Kock Architekten conciliates these The final solution combines elements of the shoe-box and of the vineyard configurations, as the audience conflicting goals by locating almost 1/3 of the required volume above the sound-transparent grid- surrounds the orchestra. The sense of intimacy is further enhanced by the concave-curved shapes ceiling (Figure 3). The final solution combines elements of the shoe-box and of the vineyard featured by the fronts and undersides of the balconies located at the sides of the venue. The APBD configurations, as the audience surrounds the orchestra. The sense of intimacy is further enhanced method informed the design of these surfaces as well as that of the acoustic canopy suspended above by the concave-curved shapes featured by the fronts and undersides of the balconies located at the the stage. The architectural team collaborated with the acoustic consultants in the design process of sides of the venue. The APBD method informed the design of these surfaces as well as that of the these elements, which was developed using parametric models created in Grasshopper and a custom acoustic canopy suspended above the stage. The architectural team collaborated with the acoustic acoustic simulation tool integrated in the modeling environment. In plan, the curved profiles of the consultants in the design process of these elements, which was developed using parametric models sides and undersides of the balconies were initially determined on the basis of two center-points, created in Grasshopper and a custom acoustic simulation tool integrated in the modeling one in the conductor ’s position and one in the middle of the parterre. In order to prevent the creation environment. In plan, the curved profiles of the sides and undersides of the balconies were initially of sound focuses and echoes resulting from the curvature, these surfaces were segmented, and the determined on the basis of two center-points, one in the conductor’s position and one in the middle curvature and vertical tilting of each portion was optimized based on acoustic simulation feedbacks of the parterre. In order to prevent the creation of sound focuses and echoes resulting from the to provide beneficial sound reflections, enhancing clarity and acoustic envelopment. The acoustic curvature, these surfaces were segmented, and the curvature and vertical tilting of each portion was canopy located above the stage is made of five double-curved and dynamically shaped panels made optimized based on acoustic simulation feedbacks to provide beneficial sound reflections, enhancing of gypsum fiber board. The form of the panels of the canopy was optimized iteratively considering clarity and acoustic envelopment. The acoustic canopy located above the stage is made of five double- acoustic and architectural goals and their final configuration, which features varying curvatures in curved and dynamically shaped panels made of gypsum fiber board. The form of the panels of the cross section, enhances the di usion of the percussion and brass in the venue. Odeon simulations were canopy was optimized iteratively considering acoustic and architectural goals and their final performed in late design phases for verification purposes and found good agreement with the results configuration, which features varying curvatures in cross section, enhances the diffusion of the of the simulations employed to support the design optimization [65–67]. percussion and brass in the venue. Odeon simulations were performed in late design phases for verification purposes and found good agreement with the results of the simulations employed to support the design optimization [65–67]. Acoustics 2020, 2 253 Acoustics 2020, 3 FOR PEER REVIEW 8 Figure 3. Anneliese Brost Musikforum Ruhr. Image courtesy © Mark Wohlrab/architektur-photos.de. Figure 3. Anneliese Brost Musikforum Ruhr. Image courtesy © Mark Wohlrab/architektur-photos.de. Concert Hall of Ureshino Cultural Center 2.2.1.4. Concert Hall of Ureshino Cultural Center Design: AnS Studio, SUEP Architects; Acoustics: Nagata Acoustics; Ureshino, Japan, 2014 Design The : An concert S Studio hall , SUEP (463 Architects seats) is part ; Aof coustic the Cultural s: Nagata Acou Center stics; of the Uresh city of ino, Ur Japan, 2014 eshino and features a shoe-box configuration with a folding roof (Figure 4). In the design of the roof of the concert hall, origami The concert hall (463 seats) is part of the Cultural Center of the city of Ureshino and features a design and acoustic engineering were combined in order to meet the acoustic performance requirements. shoe-box configuration with a folding roof (Figure 4). In the design of the roof of the concert hall, APBD informed the design of the folding roof of the venue, whose final shape is the outcome of an origami design and acoustic engineering were combined in order to meet the acoustic performance interactive design method, which combined a parametric origami software (i.e., a software able to requirements. APBD informed the design of the folding roof of the venue, whose final shape is the generate di erent folding patterns based on origami rules), a custom acoustic simulation program outcome of an interactive design method, which combined a parametric origami software (i.e., a and an optimization tool. The acoustic performance requirements for the venue proposed by the software able to generate different folding patterns based on origami rules), a custom acoustic acoustic consultants were a uniform distribution of sound over the hall and audience within 30–90 ms, simulation program and an optimization tool. The acoustic performance requirements for the venue and the absence of echoes and sound focuses. The design method followed three steps. Initially, all the proposed by the acoustic consultants were a uniform distribution of sound over the hall and audience possible design alternatives for the folding roof were generated by the origami program, according to within 30–90 ms, and the absence of echoes and sound focuses. The design method followed three origami rules and the constraints set by the design team, which were related to building regulations, steps. Initially, all the possible design alternatives for the folding roof were generated by the origami budget, structural aspects and other criteria. Each solution was then analyzed with the custom acoustic program, according to origami rules and the constraints set by the design team, which were related simulation program, with respect to the sound propagation and the distribution of sound at the to building regulations, budget, structural aspects and other criteria. Each solution was then analyzed audience positions. Finally, based on the simulation feedbacks, the optimization tool was used to find with the custom acoustic simulation program, with respect to the sound propagation and the the solution, which showed the best combination of parameters to balance architectural and acoustic distribution of sound at the audience positions. Finally, based on the simulation feedbacks, the goals. The final solution for the roof, which was selected by the optimization program among a pool of optimization tool was used to find the solution, which showed the best combination of parameters to about 200 design alternatives, is based on the Miura-ori folding pattern [68], where the folding depths balance architectural and acoustic goals. The final solution for the roof, which was selected by the and angles have been selected based on acoustic simulation feedback [28,69]. optimization program among a pool of about 200 design alternatives, is based on the Miura-ori folding pattern [68], where the folding depths and angles have been selected based on acoustic simulation feedback [28,69]. Acoustics 2020, 2 254 Acoustics 2020, 3 FOR PEER REVIEW 9 Figure 4. Concert Hall of Ureshino Cultural Center. Image courtesy © Kai Nakamura. Figure 4. Concert Hall of Ureshino Cultural Center. Image courtesy © Kai Nakamura. University of Iowa Concert Hall 2.2.1.5. University of Iowa Concert Hall Design: LMN Architects, Neumann Monson Architects. Acoustics: Ja e Holden; Iowa City, IA, USA, 2016 Design: LMN Architects, Neumann Monson Architects. Acoustics: Jaffe Holden; Iowa City, IA, USA, The 700 seats-concert hall represents the main venue of the Voxman Music Building of the University of Iowa. The concert hall is based on the shoe-box configuration and features a sculpted The 700 seats-concert hall represents the main venue of the Voxman Music Building of the structure suspended from the ceiling, made of 946 unique folded aluminum composite modules, which University of Iowa. The concert hall is based on the shoe-box configuration and features a sculpted was generated through performance-based design (Figure 5). The structure integrates and rationalizes structure suspended from the ceiling, made of 946 unique folded aluminum composite modules, in a unique and aesthetically unified solution five technical systems: acoustics, stage lighting, house which was generated through performance-based design (Figure 5). The structure integrates and lighting, audio-visual and fire protection. The form-finding process, which guided the design of the rationalizes in a unique and aesthetically unified solution five technical systems: acoustics, stage structure was enabled by a collaborative parametric model developed in Grasshopper, which was lighting, house lighting, audio-visual and fire protection. The form-finding process, which guided optimized in light of the objectives defined by the consultants of the di erent disciplines involved. the design of the structure was enabled by a collaborative parametric model developed in The project was guided by an iterative design method and was also optimized for fabrication and to be Grasshopper, which was optimized in light of the objectives defined by the consultants of the delivered in a low-bid procurement environment. As regards acoustics, the feedbacks from a custom different disciplines involved. The project was guided by an iterative design method and was also ray-tracing simulation tool, developed in collaboration with the acousticians, were used to drive the optimized for fabrication and to be delivered in a low-bid procurement environment. As regards design optimization process of the ceiling system. This enabled the architects to autonomously run acoustics, the feedbacks from a custom ray-tracing simulation tool, developed in collaboration with preliminary acoustic analyses to test the design iterations in early design phases. In particular, the form the acousticians, were used to drive the design optimization process of the ceiling system. This of the ceiling system was progressively refined to ensure an even distribution of the reflected sound enabled the architects to autonomously run preliminary acoustic analyses to test the design iterations waves towards the audience and toward the upper portion of the side walls. Given the number of in early design phases. In particular, the form of the ceiling system was progressively refined to disciplines involved, SketchUp [70] and Revit [71] versions of the parametric model had to be used ensure an even distribution of the reflected sound waves towards the audience and toward the upper to allow exchanges among the di erent consultants. Early prototypes of panels and connections of portion of the side walls. Given the number of disciplines involved, SketchUp [70] and Revit [71] the ceiling system were produced at di erent scales and tested. Iterations between physical and versions of the parametric model had to be used to allow exchanges among the different consultants. digital models were used to further refine the project and explore di erent fabrication strategies. Great Early prototypes of panels and connections of the ceiling system were produced at different scales commitment was placed in optimizing the fabrication of the system, and direct-to-fabrication data for and tested. Iterations between physical and digital models were used to further refine the project and construction could be generated from the model [72–74]. explore different fabrication strategies. Great commitment was placed in optimizing the fabrication of the system, and direct-to-fabrication data for construction could be generated from the model [72– 74]. Acoustics 2020, 2 255 Acoustics 2020, 3 FOR PEER REVIEW 10 Figure 5. University of Iowa Concert Hall. Image courtesy © Tim Grith. Figure 5. University of Iowa Concert Hall. Image courtesy © Tim Griffith. Symphony Hall of the Fuzhou Strait Culture and Art Centre 2.2.1.6. Symphony Hall of the Fuzhou Strait Culture and Art Centre Design: PES-Architects, Acoustics: Tongji Architectural Design Group, Kahle Acoustics and Akukon; Design: PE Mawei S-Archit New ects T, own, Acoust Fuzhou, ics: Ton China, gji Arch 2018 itectural Design Group, Kahle Acoustics and Akukon; Mawei The New Town, Fuzhou Strait Fuzh Cultur ou, Chi e and na, 2Art 018 Centre includes a 1000 seat symphony hall and a 1600 seat opera hall, both of which were developed with the APBD approach. The Fuzhou Strait Culture and Art Centre includes a 1000 seat symphony hall and a 1600 seat The symphony hall of the Strait Culture and Art Centre in Fuzhou features a vineyard configuration opera hall, both of which were developed with the APBD approach. and, despite the relatively modest seat capacity, is meant to host a full symphony orchestra of more The symphony hall of the Strait Culture and Art Centre in Fuzhou features a vineyard than 100 musicians (Figure 6). In order to prevent overly loud acoustics, its volume was set at 17,000 m configuration and, despite the relatively modest seat capacity, is meant to host a full symphony and was visually divided in two parts by the suspended reflectors, which overlook the audience. orchestra of more than 100 musicians (Figure 6). In order to prevent overly loud acoustics, its volume The curvature of the suspended reflectors ensures an even coverage of early reflections, but the major was set at 17,000 m and was visually divided in two parts by the suspended reflectors, which role is played by the walls of the halls, which are shaped as convex sphere portions. The walls that overlook the audience. The curvature of the suspended reflectors ensures an even coverage of early separate the terraces of the audience and those at the periphery of the hall are inclined in a petal-like reflections, but the major role is played by the walls of the halls, which are shaped as convex sphere configuration. The lower portions of these elements generate early reflections, while the upper parts portions. The walls that separate the terraces of the audience and those at the periphery of the hall spread the sound energy in the venue. The surface of the petals is coated with ceramic tiles with are inclined in a petal-like configuration. The lower portions of these elements generate early di erent textures and patterns, to provide either specular or di use reflections. The APBD approach reflections, while the upper parts spread the sound energy in the venue. The surface of the petals is informed the design of the geometrical features and surface patterns of these petals. Grasshopper was coated with ceramic tiles with different textures and patterns, to provide either specular or diffuse used to generate the parametric models, while a custom tool integrated in the modeling environment reflections. The APBD approach informed the design of the geometrical features and surface patterns was used to analyze the acoustic performance according to the early acoustic eciency approach [75]. of these petals. Grasshopper was used to generate the parametric models, while a custom tool integrated in the modeling environment was used to analyze the acoustic performance according to the early acoustic efficiency approach [75]. As regard the geometrical features, the distribution and Acoustics 2020, 2 256 Acoustics 2020, 3 FOR PEER REVIEW 11 As regard the geometrical features, the distribution and vertical tilting angles of the “petals” were vertical tilting angles of the “petals” were optimized to provide early lateral reflections to all the optimized to provide early lateral reflections to all the audience blocks. The surface pattern of specularly audience blocks. The surface pattern of specularly reflecting or diffusing ceramic tiles was used reflecting or di using ceramic tiles was used generate useful early reflections and to prevent undesired generate useful early reflections and to prevent undesired echoes from the upper portions of the echoes from the upper portions of the petals. Since it was considered crucial to maintain strong early petals. Since it was considered crucial to maintain strong early reflections, the sound diffusing tile reflections, the sound di using tile pattern was applied only in the portion of the petals creating pattern was applied only in the portion of the petals creating potentially harmful late reflections, potentially harmful late reflections, while the remaining part was left with a specularly reflective finish. while the remaining part was left with a specularly reflective finish. Such surfaces were identified by Such surfaces were identified by using a custom algorithm able to categorize the surface facets based using a custom algorithm able to categorize the surface facets based on the delay of the reflections on the delay of the reflections they may generate, considering the combined data from four sound they may generate, considering the combined data from four sound source positions. Although the source positions. Although the surfaces were identified by the algorithm, when conflicting feedbacks surfaces were identified by the algorithm, when conflicting feedbacks were found, the final decision were found, the final decision was left to the operator. Odeon simulations were used in late design was left to the operator. Odeon simulations were used in late design phases for verification purposes phases for verification purposes [76]. [76]. Figure 6. Symphony Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy© Marc Goodwin. Figure 6. Symphony Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Opera Hall of the Fuzhou Strait Culture and Art Centre 2.2.1.7. Opera Hall of the Fuzhou Strait Culture and Art Centre Design: PES-Architects, Acoustics: Tongji Architectural Design Group, Kahle Acoustics and Akukon; Mawei New Town, Fuzhou, China, 2018 Design: PES-Architects, Acoustics: Tongji Arch3 itectural Design Group, Kahle Acoustics and Akukon; The 1600-seat opera hall (volume 14,500 m ) is based on the horseshoe configuration and features Mawei New Town, Fuzhou, China, 2018 a continuous skin, with convex and concave curvatures, which defines and unifies walls, balconies and ceiling (Figure 7). The APBD approach was applied to define the form of the skin, which was optimized The 1600-seat opera hall (volume 14,500 m ) is based on the horseshoe configuration and features in order to meet the acoustic requirements of creating a homogenous coverage of strong early lateral a continuous skin, with convex and concave curvatures, which defines and unifies walls, balconies reflections over the entire audience and to avoid undesired focusing e ects. The acoustic simulations and ceiling (Figure 7). The APBD approach was applied to define the form of the skin, which was were performed with a custom tool based on a di erential ray-tracing technique [77], integrated in the optimized in order to meet the acoustic requirements of creating a homogenous coverage of strong modeling environment. Since the architectural elements are not present as individual entities but are early lateral reflections over the entire audience and to avoid undesired focusing effects. The acoustic interlinked by the skin, they could not be singularly adjusted, as any form change would impact on simulations were performed with a custom tool based on a differential ray-tracing technique [77], the other elements. Therefore, the continuous envelope was modeled parametrically in Grasshopper, integrated in the modeling environment. Since the architectural elements are not present as and directly optimized based on the acoustic feedbacks, due to the close collaboration between the individual entities but are interlinked by the skin, they could not be singularly adjusted, as any form architectural and acoustic teams. In particular, the skin was subdivided in smaller patches, and each change would impact on the other elements. Therefore, the continuous envelope was modeled was assigned with an acoustic target, such as creating early reflections or enhancing late reverberation. parametrically in Grasshopper, and directly optimized based on the acoustic feedbacks, due to the The orientation of the di erent skin portions was then iteratively optimized by the operators in order close collaboration between the architectural and acoustic teams. In particular, the skin was to achieve their target performance requirements and then combined to create the final smooth curved subdivided in smaller patches, and each was assigned with an acoustic target, such as creating early skin. A fine-scale texture of flower-shaped ceramic tiles is applied to the surfaces of the continuous skin; reflections or enhancing late reverberation. The orientation of the different skin portions was then the small irregularities of the pattern provide sound scattering at high frequencies. The final outcome iteratively optimized by the operators in order to achieve their target performance requirements and then combined to create the final smooth curved skin. A fine-scale texture of flower-shaped ceramic tiles is applied to the surfaces of the continuous skin; the small irregularities of the pattern provide Acoustics 2020, 2 257 Acoustics 2020, 3 FOR PEER REVIEW 12 of the optimization was further tested in Odeon; the verification confirmed the benefits provided by sound scattering at high frequencies. The final outcome of the optimization was further tested in the application of APBD [76,78]. Odeon; the verification confirmed the benefits provided by the application of APBD [76,78]. Figure 7. Opera Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Figure 7. Opera Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Conga Room 2.2.1.8. Conga Room Design: Belzberg Architects, Acoustics: Newson Brown Acoustics; Los Angeles, CA, USA, 2008 Design: Belzberg Architects, Acoustics: Newson Brown Acoustics; Los Angeles, CA, USA, 2008 The Conga Room dance club hosts a series of a multitude of programs (dance hall, stage, restaurant, bars and VIP areas) and is located at the second floor of a multipurpose building, mainly The Conga Room dance club hosts a series of a multitude of programs (dance hall, stage, occupied by oces. Due to a retrofit intervention, the existing spaces were acoustically insulated restaurant, bars and VIP areas) and is located at the second floor of a multipurpose building, mainly and adapted to host the new mixed functions. The bold design of the undulating ceiling system is occupied by offices. Due to a retrofit intervention, the existing spaces were acoustically insulated and meant to visually attract clients while also providing acoustic treatment for the dance hall (Figure 8). adapted to host the new mixed functions. The bold design of the undulating ceiling system is meant The ceiling was indeed identified as the most e ective location for acoustic treatments to provide to visually attract clients while also providing acoustic treatment for the dance hall (Figure 8). The sound insulation and amplification. The ceiling system was developed through performance-based ceiling was indeed identified as the most effective location for acoustic treatments to provide sound design, exploiting the functions o ered by CATIA [79] and Rhinoceros for modeling, and Ecotect [80] insulation and amplification. The ceiling system was developed through performance-based design, for the simulations. The ceiling system, made of CNC-milled plywood panels whose pattern and exploiting the functions offered by CATIA [79] and Rhinoceros for modeling, and Ecotect [80] for the fashion changes di erentiate the various environments of the club, was designed to address acoustic simulations. The ceiling system, made of CNC-milled plywood panels whose pattern and fashion issues and to integrate several building infrastructures (house lighting, mechanical, audio-visual, fire changes differentiate the various environments of the club, was designed to address acoustic issues protection, etc.). The model of the ceiling structure was iteratively optimized based on the feedback and to integrate several building infrastructures (house lighting, mechanical, audio-visual, fire from the various specialists involved and performance simulation. In particular, the ceiling panels protection, etc.). The model of the ceiling structure was iteratively optimized based on the feedback over the dance hall are morphed into flower-like structures, which control the acoustic performance of from the various specialists involved and performance simulation. In particular, the ceiling panels the ceiling. The di erent arrangements and tilting of the flowers’ petals have been optimized based on over the dance hall are morphed into flower-like structures, which control the acoustic performance acoustic simulation feedback to provide the desired amount of sound absorption [81–84]. of the ceiling. The different arrangements and tilting of the flowers’ petals have been optimized based on acoustic simulation feedback to provide the desired amount of sound absorption [81–84]. Acoustics 2020, 2 258 Acoustics 2020, 3 FOR PEER REVIEW 13 Figure 8. Conga Room. Image courtesy © Benny Chan/Fotoworks. Figure 8. Conga Room. Image courtesy © Benny Chan/Fotoworks. Stage by the Sea 2.2.1.9. Stage by the Sea Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; Littlehampton, UK, 2014 The project consists of two double-curved concrete shells located close to the coastline of Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; Littlehampton, UK, 2014 Littlehampton, United Kingdom. The smaller shell works as a shelter, while the bigger one is an The project consists of two double-curved concrete shells located close to the coastline of acoustic shell that is used as a stage for outdoor concerts and projects the sounds towards the listeners Littlehampton, United Kingdom. The smaller shell works as a shelter, while the bigger one is an (Figure 9). During the design process of the acoustic shell, great commitment was placed in combining acoustic shell that is used as a stage for outdoor concerts and projects the sounds towards the listeners structural, acoustics and aesthetic goals in a unique solution. The final design of the acoustic shell is the (Figure 9). During the design process of the acoustic shell, great commitment was placed in result of an ABPD process, and conjugates the key acoustic performance requirements with architectural combining structural, acoustics and aesthetic goals in a unique solution. The final design of the and structural objectives to create a durable, e ective and inexpensive solution. The design process acoustic shell is the result of an ABPD process, and conjugates the key acoustic performance involved the use of Grasshopper for Rhinoceros for modeling, Dynamo for Revit [71,85] for the acoustic requirements with architectural and structural objectives to create a durable, effective and simulations and Galapagos for the design optimization. The design of the structure was developed in inexpensive solution. The design process involved the use of Grasshopper for Rhinoceros for a tight collaboration between architects and technical consultants, which enabled us to find the best modeling, Dynamo for Revit [71,85] for the acoustic simulations and Galapagos for the design compromise in overall terms. The digital model of the shell was exchanged among the professionals optimization. The design of the structure was developed in a tight collaboration between architects involved more than twenty times before its final configuration was achieved. The acoustic analysis and technical consultants, which enabled us to find the best compromise in overall terms. The digital enabled one to define a shape for the acoustic shell able to e ectively support outdoor concerts by model of the shell was exchanged among the professionals involved more than twenty times before reflecting the sounds towards the audience located in the facing sunken garden, allowing the music to its final configuration was achieved. The acoustic analysis enabled one to define a shape for the be perfectly heard in windy conditions at a distance of 50 m from the stage [86–90]. acoustic shell able to effectively support outdoor concerts by reflecting the sounds towards the audience located in the facing sunken garden, allowing the music to be perfectly heard in windy conditions at a distance of 50 m from the stage [86–90]. Acoustics 2020, 2 259 Acoustics 2020, 3 FOR PEER REVIEW 14 Figure Figure 9. 9. Stage Stage by the Sea by the Sea.. Im Image age cour courtesy tesy © © Flanagan Lawrence. Flanagan Lawrence. Resonant String Shell (ReS) 6.0 2.2.1.10. Resonant String Shell (ReS) 6.0 Design: Sergio Pone, Bianca Parenti, Daniele Lancia, Sofia Colabella; Acoustics: Serafino Di Design: Sergio Pone, Bianca Parenti, Daniele Lancia, Sofia Colabella; Acoustics: Serafino Di Rosario; Rosario; Acireale, Italy, 2017 Acireale, Italy, 2017 ReS is a temporary outdoor acoustic shell that hosts the classical music concerts of the yearly festival “Villa Pennisi in Musica”. The shell design combines acoustic concerns with structural and ReS is a temporary outdoor acoustic shell that hosts the classical music concerts of the yearly technological ones. During each edition of the festival, a prototype of a temporary outdoor acoustic festival “Villa Pennisi in Musica”. The shell design combines acoustic concerns with structural and shell is built in the framework of a summer school, and its performances are tested though acoustic technological ones. During each edition of the festival, a prototype of a temporary outdoor acoustic measurements. From year to year, the design of the shell is optimized based on the measured acoustic shell is built in the framework of a summer school, and its performances are tested though acoustic performance and a new design is developed to be built in the following edition. The acoustic shell built measurements. From year to year, the design of the shell is optimized based on the measured acoustic in 2017, named ReS 6.0 (Figure 10), was developed exploiting a multiobjective optimization process performance and a new design is developed to be built in the following edition. The acoustic shell to define the geometry of the shell. In particular, the inner profile of the shell, which is composed built in 2017, named ReS 6.0 (Figure 10), was developed exploiting a multiobjective optimization by wooden reflective panels, anchored to an already defined structural system made of arches, was process to define the geometry of the shell. In particular, the inner profile of the shell, which is optimized within a magnitude of 50 cm. The process was enabled by Octopus [25], a multiobjective composed by wooden reflective panels, anchored to an already defined structural system made of optimization tool, Grasshopper and a custom acoustic simulation tool based on an image-source arches, was optimized within a magnitude of 50 cm. The process was enabled by Octopus [25], a method. Considering three pairs of sound sources located within the shell (i.e., music performers), multiobjective optimization tool, Grasshopper and a custom acoustic simulation tool based on an the profile of the shell was optimized to maximize the evenness of sound energy in the audience image-source method. Considering three pairs of sound sources located within the shell (i.e., music positions. The sound energy was described by the sound pressure level and the standard deviation was performers), the profile of the shell was optimized to maximize the evenness of sound energy in the calculated to quantify its rate of homogeneity. For each couple of sound sources, the sound pressure audience positions. The sound energy was described by the sound pressure level and the standard level has been estimated using the custom acoustic simulation tool, and Galapagos was used to search deviation was calculated to quantify its rate of homogeneity. For each couple of sound sources, the for solutions able to minimize the standard deviation. The optimization process identified a set of sound pressure level has been estimated using the custom acoustic simulation tool, and Galapagos “equally optimal” solutions, among which the final configuration was selected by considering also was used to search for solutions able to minimize the standard deviation. The optimization process aesthetic criteria. CATT-Acoustic was used in late design phases to run more accurate analyses of the identified a set of “equally optimal” solutions, among which the final configuration was selected by optimized shell. The field measurement confirmed that the form optimization leads to a greater and considering also aesthetic criteria. CATT-Acoustic was used in late design phases to run more more uniform distribution of sound energy in the audience [46]. accurate analyses of the optimized shell. The field measurement confirmed that the form optimization leads to a greater and more uniform distribution of sound energy in the audience [46]. Acoustics 2020, 2 260 Acoustics 2020, 3 FOR PEER REVIEW 15 Figure 10. ReS 6.0. Image courtesy © Daniele Lancia. Figure 10. ReS 6.0. Image courtesy © Daniele Lancia. Soundforms 2.2.1.11. Soundforms Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; London, UK, 2012 Soundforms is a movable acoustic shell designed to support outdoor classic music performances, Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; London, UK, 2012 by improving the ability of musicians of the ensemble to hear each other, and by projecting the sound Soundforms is a movable acoustic shell designed to support outdoor classic music generated towards the audience. A prototype of the shell, developed for small chamber music orchestra, performances, by improving the ability of musicians of the ensemble to hear each other, and by was built and tested in London’s Dockland, and was then selected to be installed in the Olympic Park projecting the sound generated towards the audience. A prototype of the shell, developed for small for the 2012 London Olympic Games to host music concerts during the event (Figure 11). The acoustic chamber music orchestra, was built and tested in London’s Dockland, and was then selected to be performances were one of the major drivers of the design process, aside with the development of installed in the Olympic Park for the 2012 London Olympic Games to host music concerts during the the structure and its optimization for transport and assembly. The shell form was developed from a event (Figure 11). The acoustic performances were one of the major drivers of the design process, portion of torus, and features an upper peak, which was designed to project as much sound as possible aside with the development of the structure and its optimization for transport and assembly. The towards the listeners, playing a role similar to that of the ceilings of concert halls. The shell has an shell form was developed from a portion of torus, and features an upper peak, which was designed inflatable skin made of eight PVC coated polyester cushions, fixed to the truss structure. The side walls to project as much sound as possible towards the listeners, playing a role similar to that of the ceilings of the acoustic shell, which performs as reflectors, are integrated in the inner structure of the shell and of concert halls. The shell has an inflatable skin made of eight PVC coated polyester cushions, fixed are visually covered by an acoustically transparent fabric liner, thus enabling one to maintain the visual to the truss structure. The side walls of the acoustic shell, which performs as reflectors, are integrated aspects of the shell without compromising their acoustic performances. Removable reflective panels are in the inner structure of the shell and are visually covered by an acoustically transparent fabric liner, installed within the shell, with the objective to balance the amount of sound energy di used towards thus enabling one to maintain the visual aspects of the shell without compromising their acoustic the orchestra and projected towards the audience. The APBD method informed the development of performances. Removable reflective panels are installed within the shell, with the objective to balance the convex profiles of the reflectors, as well as their deployment within the shell, which, in the built the amount of sound energy diffused towards the orchestra and projected towards the audience. The prototype, were optimized for a small chamber orchestra. The optimized reflectors were developed by APBD method informed the development of the convex profiles of the reflectors, as well as their the acoustic consultants in close collaboration with the design team, following a process of subsequent deployment within the shell, which, in the built prototype, were optimized for a small chamber optimization combining architectural and acoustic objectives with fabrication and constructability orchestra. The optimized reflectors were developed by the acoustic consultants in close collaboration criteria. The reflectors facets were parameterized in Grasshopper, the acoustic simulations were run with the design team, following a process of subsequent optimization combining architectural and using a custom ray-tracing script in Dynamo for Revit, while the optimization process was performed acoustic objectives with fabrication and constructability criteria. The reflectors facets were with the support of automated routines using Galapagos. The final solution was then further tested in parameterized in Grasshopper, the acoustic simulations were run using a custom ray-tracing script Odeon to validate the results [27,91–93]. in Dynamo for Revit, while the optimization process was performed with the support of automated routines using Galapagos. The final solution was then further tested in Odeon to validate the results [27,91–93]. Acoustics 2020, 2 261 Acoustics 2020, 3 FOR PEER REVIEW 16 Figure 11. Soundforms. Image courtesy © Nick Guttridge. Figure 11. Soundforms. Image courtesy © Nick Guttridge. Tiara Acoustic Shell 2.2.1.12. Tiara Acoustic Shell Design and acoustics: Alban Bausset, Willem Boning, Arup Acoustics; Fishtail, MT, USA, 2014–2015 The design of the acoustical shell for the Tippet Rise Art Center was commissioned to Arup Design and acoustics: Alban Bausset, Willem Boning, Arup Acoustics; Fishtail, MT, USA, 2014–2015 Acoustics in 2014. The demountable and transportable shell was initially designed to host and support The design of the acoustical shell for the Tippet Rise Art Center was commissioned to Arup outdoor chamber music concerts for an audience of 50–60 people, by creating an intimate performance Acoustics in 2014. The demountable and transportable shell was initially designed to host and space, visually open to the surroundings natural environment (Figure 12). The shell is made of wooden support outdoor chamber music concerts for an audience of 50–60 people, by creating an intimate panels, which represent the upper corners of the side and front corners of a fan-shaped room, while the performance space, visually open to the surroundings natural environment (Figure 12). The shell is rest of the enclosing surfaces were removed to open the view towards the natural setting. made of wooden panels, which represent the upper corners of the side and front corners of a fan- The goal was to generate a unified acoustic environment for both audience and performers and shaped room, while the rest of the enclosing surfaces were removed to open the view towards the an enveloping sound impression, despite the lack of reverberation. The virtual model of the shell was natural setting. parameterized using Grasshopper. The acoustic performances of the structure were investigated using The goal was to generate a unified acoustic environment for both audience and performers and a custom simulation tool based on an image-source method; a source position and 50 receiver positions an enveloping sound impression, despite the lack of reverberation. The virtual model of the shell was were used. Based on the performance feedbacks, Galapagos was used to optimize the parametric parameterized using Grasshopper. The acoustic performances of the structure were investigated model by adjusting six parameters controlling the shell form, in order to ensure a broad spread of using a custom simulation tool based on an image-source method; a source position and 50 receiver early energy over the entire audience. The variation space of the model parameters was set based on positions were used. Based on the performance feedbacks, Galapagos was used to optimize the structural requirements, and in order to prevent the shell from obscuring the view of the mountain parametric model by adjusting six parameters controlling the shell form, in order to ensure a broad in the background. The fitness function counted the second and third order of reflections over the spread of early energy over the entire audience. The variation space of the model parameters was set “poorest” receivers of the audience. From the two solution regions found by Galapagos, the design based on structural requirements, and in order to prevent the shell from obscuring the view of the team selected the final one based on structural criteria. In 2015, the initial design solution was further mountain in the background. The fitness function counted the second and third order of reflections expanded in order to accommodate up to 80 people, by the addition of two kinks to the structure, which over the “poorest” receivers of the audience. From the two solution regions found by Galapagos, the were optimized with a procedure similar to that used for the initial solution. The final configuration of design team selected the final one based on structural criteria. In 2015, the initial design solution was the shell provides on average 5.6 s- and third-order reflections to each receiver, with a minimum of one further expanded in order to accommodate up to 80 people, by the addition of two kinks to the from the front, one from the right side and one from the left side [94]. structure, which were optimized with a procedure similar to that used for the initial solution. The final configuration of the shell provides on average 5.6 s- and third-order reflections to each receiver, with a minimum of one from the front, one from the right side and one from the left side [94]. Acoustics 2020, 2 262 Acoustics 2020, 3 FOR PEER REVIEW 17 Figure 12. Tippet Rise Art Center, MT. Photo: Erik Petersen © 2017 Tippet Rise. Figure 12. Tippet Rise Art Center, MT. Photo: Erik Petersen © 2017 Tippet Rise. Aalborg Acoustic Pavilion 2011 2.2.1.13. Aalborg Acoustic Pavilion 2011 Design and acoustics: AREA, Electrotexture Lab; Aalborg, Denmark, 2011 The temporary acoustic pavilion was developed within a research framework. The structure is Design and acoustics: AREA, Electrotexture Lab; Aalborg, Denmark, 2011 meant to host electronic music performance and its design was optimized for both acoustic performances The temporary acoustic pavilion was developed within a research framework. The structure is and constructive feasibility. The structure is composed by CNC milled plywood plates, which works meant to host electronic music performance and its design was optimized for both acoustic as sound reflectors (Figure 13). The design process was enabled by the combined use of Grasshopper, performances and constructive feasibility. The structure is composed by CNC milled plywood plates, a custom acoustic simulation tool and Galapagos solver, which allowed one to combine acoustic goals which works as sound reflectors (Figure 13). The design process was enabled by the combined use of with production and assembly criteria. The pavilion was also optimized with the aim to open its Grasshopper, a custom acoustic simulation tool and Galapagos solver, which allowed one to combine geometry towards the water while closing it towards the close-by road, to shield it from trac noise. acoustic goals with production and assembly criteria. The pavilion was also optimized with the aim During the design process, the design problem has been progressively reformulated, in order to reduce to open its geometry towards the water while closing it towards the close-by road, to shield it from the variation space evaluated by the Galapagos solver. With respect to acoustics, the volume of the traffic noise. During the design process, the design problem has been progressively reformulated, in pavilion and the configuration of the reflectors, which define the envelope of the shell, were optimized order to reduce the variation space evaluated by the Galapagos solver. With respect to acoustics, the in two subsequent steps. In order to prevent the structure from altering the electronic music spread volume of the pavilion and the configuration of the reflectors, which define the envelope of the shell, via a loudspeaker, the optimization processes aimed to minimize the reverberation time within the were optimized in two subsequent steps. In order to prevent the structure from altering the electronic pavilion, calculated with the Sabine equation. This goal was reached by maximizing the number music spread via a loudspeaker, the optimization processes aimed to minimize the reverberation time of reflections occurring among reflectors, thus enhancing sound absorption, and by directing the within the pavilion, calculated with the Sabine equation. This goal was reached by maximizing the reflected sound away from the pavilion. The optimization was performed considering di erent sound number of reflections occurring among reflectors, thus enhancing sound absorption, and by directing source positions, which marked the loudspeaker locations in the corners of the pavilion. In particular, the reflected sound away from the pavilion. The optimization was performed considering different the arrangement of the specific set of reflectors serving each loudspeaker was optimized to maximize sound source positions, which marked the loudspeaker locations in the corners of the pavilion. In sound absorption by increasing the number of reciprocal reflections. In the end, the final solution was particular, the arrangement of the specific set of reflectors serving each loudspeaker was optimized slightly refined to meet the fabrication requirements [95,96]. to maximize sound absorption by increasing the number of reciprocal reflections. In the end, the final solution was slightly refined to meet the fabrication requirements [95,96]. Acoustics 2020, 2 263 Acoustics 2020, 3 FOR PEER REVIEW 18 Figure 13. Aalborg Acoustic Pavilion 2011. Image courtesy © Isak Worre Foged. Figure 13. Aalborg Acoustic Pavilion 2011. Image courtesy © Isak Worre Foged. Aalborg Acoustic Pavilion 2012 2.2.1.14. Aalborg Acoustic Pavilion 2012 Design and acoustics: AREA, Mads Brath Jensen; Aalborg, Denmark, 2012 The pavilion is composed of an origami folded structure made of triangular wooden panels Design and acoustics: AREA, Mads Brath Jensen; Aalborg, Denmark, 2012 (Figure 14). The temporary pavilion was developed for research purposes and is intended to host The pavilion is composed of an origami folded structure made of triangular wooden panels two subspaces with di erent purposes, which are therefore characterized by dissimilar acoustic (Figure 14). The temporary pavilion was developed for research purposes and is intended to host two performances. A design optimization process was set in the in order to create two areas with opposite subspaces with different purposes, which are therefore characterized by dissimilar acoustic acoustic proprieties within the pavilion: a zone intended for classical music performances, featuring a performances. A design optimization process was set in the in order to create two areas with opposite long reverberation time, and an area intended for speech, with a short reverberation time. The tools acoustic proprieties within the pavilion: a zone intended for classical music performances, featuring used in the development of the acoustic pavilion are Grasshopper, a custom acoustic simulation a long reverberation time, and an area intended for speech, with a short reverberation time. The tools tool and Galapagos solver. The acoustic performances on the listener positions were described by used in the development of the acoustic pavilion are Grasshopper, a custom acoustic simulation tool the reverberation time, calculated with the Millington-Sette equation, and by sound pressure level, and Galapagos solver. The acoustic performances on the listener positions were described by the simulated using a custom ray-tracing tool. The parametric model of the pavilion was composed reverberation time, calculated with the Millington-Sette equation, and by sound pressure level, by two subsystems: the first controls the overall space form, which resemble a tunnel; the second simulated using a custom ray-tracing tool. The parametric model of the pavilion was composed by defines the folding structure and presents a higher control point resolution. The panels of the pavilion two subsystems: the first controls the overall space form, which resemble a tunnel; the second defines feature a sandwich structure with foam in the middle layer and plywood on both sides. Three panel the folding structure and presents a higher control point resolution. The panels of the pavilion feature variants were developed in order to provide three di erent rates of sound absorption, by opportunely a sandwich structure with foam in the middle layer and plywood on both sides. Three panel variants perforating the interior plywood side of the panel, and therefore exposing the sound absorptive foam were developed in order to provide three different rates of sound absorption, by opportunely layer to the impinging sound waves. The optimization process was able to control the orientations perforating the interior plywood side of the panel, and therefore exposing the sound absorptive foam of the control point of the primary and secondary subsystems, as well as the acoustic variants of the layer to the impinging sound waves. The optimization process was able to control the orientations of wooden panels, which compose of the structure. After 700 iterations, the reverberation times in the the control point of the primary and secondary subsystems, as well as the acoustic variants of the two subzones of the design solutions generated by the optimization process stabilize at values of 0.2 s wooden panels, which compose of the structure. After 700 iterations, the reverberation times in the and 1.4 s [97]. two subzones of the design solutions generated by the optimization process stabilize at values of 0.2 s and 1.4 s [97]. Acoustics 2020, 2 264 Acoustics 2020, 3 FOR PEER REVIEW 19 Figure 14. Aalborg Acoustic Pavilion 2012. Image courtesy © Isak Worre Foged. Figure 14. Aalborg Acoustic Pavilion 2012. Image courtesy © Isak Worre Foged. Resonant Chamber 2.2.1.15. Resonant Chamber Design: RVTR; Acoustics: Arup Acoustics; Ann Arbor, MI, USA, 2012 Resonant Chamber is a responsive acoustic envelope system, based on rigid origami principles, Design: RVTR; Acoustics: Arup Acoustics; Ann Arbor, MI, USA, 2012 that is able to dynamically alter the sound environment in which it is installed based on a set of inputs Resonant Chamber is a responsive acoustic envelope system, based on rigid origami principles, collected in real time by sensors or using preprogrammed configurations (Figure 15). The flexible that is able to dynamically alter the sound environment in which it is installed based on a set of inputs structure can be deployed in a music venue to alter the sound during the performance, playing the role collected in real time by sensors or using preprogrammed configurations (Figure 15). The flexible of an instrument at the architectural scale itself, or can be installed in more ordinary spaces, to calibrate structure can be deployed in a music venue to alter the sound during the performance, playing the their acoustic performances to given requirements. The faceted “sound cloud” is able to dynamically role of an instrument at the architectural scale itself, or can be installed in more ordinary spaces, to transform its configuration in response to acoustic changing conditions and to variations in the listeners’ calibrate their acoustic performances to given requirements. The faceted “sound cloud” is able to positions. The tools used to develop the project were Grasshopper, a ray-tracing tool for acoustic dynamically transform its configuration in response to acoustic changing conditions and to variations simulations and Kangaroo [98], to model the dynamic deformation of the system. The structure is in the listeners’ positions. The tools used to develop the project were Grasshopper, a ray-tracing tool made of a combination of di erent plywood panels, featuring either sound reflective, sound absorbing for acoustic simulations and Kangaroo [98], to model the dynamic deformation of the system. The or electroacoustic properties, arranged around an electronic panel that contains circuit controls and structure is made of a combination of different plywood panels, featuring either sound reflective, sensing inputs. In response to the inputs, such as ideal reverberation time, absorption coecient, sound absorbing or electroacoustic properties, arranged around an electronic panel that contains directional amplification and early/late acoustic response, the system adjusts its acoustic properties. circuit controls and sensing inputs. In response to the inputs, such as ideal reverberation time, In particular, resonant chamber modifies the acoustic performances of the space within which it is absorption coefficient, directional amplification and early/late acoustic response, the system adjusts installed by gross deformations of its shape, able to alter the aural volume, and by locally adjusting the its acoustic properties. In particular, resonant chamber modifies the acoustic performances of the folding configuration, to change the panels exposed to the sound waves. The optimal geometry and space within which it is installed by gross deformations of its shape, able to alter the aural volume, the characteristics of the materials were determined by acoustic simulations and measurements on and by locally adjusting the folding configuration, to change the panels exposed to the sound waves. physical prototypes [99–103]. The optimal geometry and the characteristics of the materials were determined by acoustic simulations and measurements on physical prototypes [99–103]. Acoustics 2020, 2 265 Acoustics 2020, 3 FOR PEER REVIEW 20 Figure 15. Resonant Chamber. Image courtesy RVTR © Adam Smith. Figure 15. Resonant Chamber. Image courtesy RVTR © Adam Smith. Courtyard Enclosure of Smithsonian Institute 2.2.1.16. Courtyard Enclosure of Smithsonian Institute Design and acoustics: Foster + Partners; Washington, DC, USA, 2007 Design The an design d acoustics of the : Fo courtyar ster + Pd artners; Wa enclosure shi fornthe gton, DC, Smithsonian USA, 20 Institute’s 07 Patent Oce, an historic building in Washington, was developed in the framework of an invited international competition, The design of the courtyard enclosure for the Smithsonian Institute’s Patent Office, an historic won by Foster + Partners. APBD informed the design of the courtyard enclosure, which is a complex building in Washington, was developed in the framework of an invited international competition, roof structure meant to perform at the same time as a solar shade, an acoustic absorber and a weather won by Foster + Partners. APBD informed the design of the courtyard enclosure, which is a complex protection device. The proposal consists of a glazed undulated canopy, which features a diagonal grid roof structure meant to perform at the same time as a solar shade, an acoustic absorber and a weather of structural beams and is supported by eight columns arranged in three domes (Figure 16). Since the protection device. The proposal consists of a glazed undulated canopy, which features a diagonal space underneath was meant to be flexible and hosts a variety of events, such as receptions, seated grid of structural beams and is supported by eight columns arranged in three domes (Figure 16). dinners and music and theatrical performances, the acoustic treatment was integrated in the bearing Since the space underneath was meant to be flexible and hosts a variety of events, such as receptions, structure of the canopy. The Specialist Modeling Group, a research team within Foster + Partners, seated dinners and music and theatrical performances, the acoustic treatment was integrated in the developed a custom generative script able to control the entire roof system based on a set of parameters, bearing structure of the canopy. The Specialist Modeling Group, a research team within Foster + allowing for exploration of a wide range of design alternatives. During the design process, the di erent Partners, developed a custom generative script able to control the entire roof system based on a set design goals were mutually related and synthesized by the generative tool, which was constantly of parameters, allowing for exploration of a wide range of design alternatives. During the design adapted as the design requirements became more specific. The acoustic performance goal was to process, the different design goals were mutually related and synthesized by the generative tool, reduce the reverberation time between 2 and 3.5 s. To this aim, the structural beams of the canopy which was constantly adapted as the design requirements became more specific. The acoustic were designed to work as sound absorbing devices. The sound absorbing layers of mineral wool performance goal was to reduce the reverberation time between 2 and 3.5 s. To this aim, the structural were mounted at the sides of the core steel structure of the beam and were covered by layer of thin beams of the canopy were designed to work as sound absorbing devices. The sound absorbing layers of mineral wool were mounted at the sides of the core steel structure of the beam and were covered by layer of thin steel tubes. The latter layer, while visually hiding the sound absorbing material, is Acoustics 2020, 2 266 Acoustics 2020, 3 FOR PEER REVIEW 21 steel tubes. The latter layer, while visually hiding the sound absorbing material, is “transparent” to sound, exposing the sound absorbing filling to the impinging sound waves. To provide the desired “transparent” to sound, exposing the sound absorbing filling to the impinging sound waves. To reduction of reverberation time, the area of the sound absorbing material was a key parameter in provide the desired reduction of reverberation time, the area of the sound absorbing material was a the generating algorithm. Although acoustic simulations were not integrated in the modeling tool, key parameter in the generating algorithm. Although acoustic simulations were not integrated in the the digital models of the enclosure could be easily exported to be analyzed in the external software. modeling tool, the digital models of the enclosure could be easily exported to be analyzed in the Ultimately, the final solution for the roof was the result of more 400 design iterations explored during a external software. Ultimately, the final solution for the roof was the result of more 400 design period of 6 months [104–107]. iterations explored during a period of 6 months [104–107]. Figure Figure 16. 16. Courtyar Courtyard Enclosu d Enclosur re e of Sm of Smithsonian ithsonian Institu Institute. te. Image Image cou courtesy rtesy © © Brady Brady Peter Peters. s. 2.2.2. Other Spaces 2.2.2. Other Spaces FabPod 2.2.2.1. FabPod Design and acoustics: Nick Williams, Brady Peters, John Cherrey, Jane Burry, Mark Burry, Design and acoustics: Nick Williams, Brady Peters, John Cherrey, Jane Burry, Mark Burry, Alexander Alexander Peña De León, Daniel Davis; Melbourne, Australia, 2013 Peña De León, Daniel Davis; Melbourne, Australia, 2013 The project is an acoustic enclosure for meetings, able to host eight people, housed in an open-plan oce at RMIT University (Figure 17). The FabPod project is part of a research investigating the The project is an acoustic enclosure for meetings, able to host eight people, housed in an open- sound di using properties of hyperboloid surfaces, which was previously explored on a prototype plan office at RMIT University (Figure 17). The FabPod project is part of a research investigating the wall in 2011. The acoustic design imperatives were to reduce the sound transmission through the sound diffusing properties of hyperboloid surfaces, which was previously explored on a prototype enclosure and to provide a homogeneous internal acoustics that was conductive to small meetings, wall in 2011. The acoustic design imperatives were to reduce the sound transmission through the without creating an acoustically “dead” space. In order to meet these objectives, the FabPod combines enclosure and to provide a homogeneous internal acoustics that was conductive to small meetings, sound absorption and sound di usion within the cell, creating a di use sound field by exploiting without creating an acoustically “dead” space. In order to meet these objectives, the FabPod combines the sound scattering properties of hyperboloid surfaces. A similar strategy was applied also to the sound absorption and sound diffusion within the cell, creating a diffuse sound field by exploiting the outer side of the installation, with the aim to improve the auditory experience in its surroundings. sound scattering properties of hyperboloid surfaces. A similar strategy was applied also to the outer The project is intended as a flexible structure, able to be applied to a range of scenarios, and therefore side of the installation, with the aim to improve the auditory experience in its surroundings. The project is intended as a flexible structure, able to be applied to a range of scenarios, and therefore great consideration was dedicated to fabrication quality and mass-customization. APBD was applied to the definition of the overall enclosure form and to the geometrical and material properties of the Acoustics 2020, 2 267 great consideration was dedicated to fabrication quality and mass-customization. APBD was applied Acoustics 2020, 3 FOR PEER REVIEW 22 to the definition of the overall enclosure form and to the geometrical and material properties of the surface pattern. Three material options were developed for the facets of the interior surface (plexiglass, surface pattern. Three material options were developed for the facets of the interior surface metal and felt), featuring di erent rates of absorption. The parametric model of the structure was (plexiglass, metal and felt), featuring different rates of absorption. The parametric model of the defined in Grasshopper and four di erent workflows were developed, each one using a di erent structure was defined in Grasshopper and four different workflows were developed, each one using acoustic simulation tool, to design either the enclosure form or the pattern of hyperboloid blocks. a different acoustic simulation tool, to design either the enclosure form or the pattern of hyperboloid Pachyderm Acoustics and Odeon, which are based on geometrical acoustics, were used to analyze the blocks. Pachyderm Acoustics and Odeon, which are based on geometrical acoustics, were used to form of the enclosure, and two custom wave-based acoustic simulation tools were used to simulate analyze the form of the enclosure, and two custom wave-based acoustic simulation tools were used the acoustic performance of the hyperboloid surfaces. Di erent acoustic parameters were taken into to simulate the acoustic performance of the hyperboloid surfaces. Different acoustic parameters were account, including reverberation time, sound pressure level, speech transmission index (STI) and the taken into account, including reverberation time, sound pressure level, speech transmission index scattering coecient. The final design consists in a semi-enclosed envelope, which wraps around the (STI) and the scattering coefficient. The final design consists in a semi-enclosed envelope, which meeting area and is composed by an irregular pattern of 180 unique hyperboloid blocks, featuring wraps around the meeting area and is composed by an irregular pattern of 180 unique hyperboloid di erent acoustic properties [108–113]. blocks, featuring different acoustic properties [108–113]. Figure 17. FabPod. Image courtesy © John Gollings. Figure 17. FabPod. Image courtesy © John Gollings. Manufacturing Parametric Acoustic Surfaces (MPAS) Project 2.2.2.2. Manufacturing Parametric Acoustic Surfaces (MPAS) project Design and acoustics: Brady Peters, Martin Tamke (CITA); Barcelona, Spain, 2010 The temporary project was installed at the Smart Geometry 2010 Workshop and Conference and Design and acoustics: Brady Peters, Martin Tamke (CITA); Barcelona, Spain, 2010 consists of a curved wall composted of di erent panel types, which generates di erent types of acoustic The temporary project was installed at the Smart Geometry 2010 Workshop and Conference and subspaces (Figure 18). The project explores new forms and material compositions and digital fabrication consists of a curved wall composted of different panel types, which generates different types of techniques. The APBD approach was applied to the design of the undulating from of the wall and to acoustic subspaces (Figure 18). The project explores new forms and material compositions and digital the panel composition. The design of the installation was developed in GenerativeComponents with fabrication techniques. The APBD approach was applied to the design of the undulating from of the the support of generative computer scripts, while acoustic simulations were run in Odeon. The acoustic wall and to the panel composition. The design of the installation was developed in goal was to create di erent acoustic subspaces in the surroundings of the installation: from a quiet, GenerativeComponents with the support of generative computer scripts, while acoustic simulations enclosed area, characterized by a high rate of sound absorption, to an amplified sound area, generated were run in Odeon. The acoustic goal was to create different acoustic subspaces in the surroundings by sound reflective surfaces, with a gradient of acoustic performance between the two conditions. of the installation: from a quiet, enclosed area, characterized by a high rate of sound absorption, to Such di erent acoustic performances could not be e ectively described by the reverberation time an amplified sound area, generated by sound reflective surfaces, with a gradient of acoustic alone; therefore, a number of other acoustic parameters were introduced in the analyses, such as early performance between the two conditions. Such different acoustic performances could not be decay time, speech transmission index and sound pressure level. Moreover, auralizations were used to effectively described by the reverberation time alone; therefore, a number of other acoustic parameters were introduced in the analyses, such as early decay time, speech transmission index and sound pressure level. Moreover, auralizations were used to listen to the sonic environments generated by the installation prior to its construction. The acoustic performances drove the design of both the overall shape of the installation and its panel composition. Nine panel types with different Acoustics 2020, 2 268 listen to the sonic environments generated by the installation prior to its construction. The acoustic Acoustics 2020, 3 FOR PEER REVIEW 23 performances drove the design of both the overall shape of the installation and its panel composition. Nine panel types with di erent acoustic performances were designed and opportunely integrated in acoustic performances were designed and opportunely integrated in manufacturing parametric manufacturing parametric acoustic surfaces (MPAS) in order to produce the desired acoustic e ects. acoustic surfaces (MPAS) in order to produce the desired acoustic effects. The collection of panel The collection of panel typologies includes a sound absorbing panel, di erent types of sound di using typologies includes a sound absorbing panel, different types of sound diffusing panels, variously panels, variously perforated screens, a panel with di erent properties depending on the direction of perforated screens, a panel with different properties depending on the direction of the impinging the impinging sound and a “sound window”, which provided visual connection from one acoustic sound and a “sound window”, which provided visual connection from one acoustic space to the space to the other. Based on acoustic performance feedbacks, the geometrical form of the wall and its other. Based on acoustic performance feedbacks, the geometrical form of the wall and its panel panel composition were controlled to generate the di erent acoustic subspaces in the surroundings of composition were controlled to generate the different acoustic subspaces in the surroundings of the the installation [104,114–116]. installation [104,114–116]. Figure 18. MPAS project. Image courtesy © Brady Peters. Figure 18. MPAS project. Image courtesy © Brady Peters. Distortion II 2.2.2.3. Distortion II Design and acoustics: Brady Peters, Martin Tamke, Stig Nielsen (CITA); Niels Jacubiak Andersen (Krydsrum); Magnus Gustafson and Patric Gustafson (Akustikmiljo)); Copenhagen, Denmark, 2011 Design and acoustics: Brady Peters, Martin Tamke, Stig Nielsen (CITA); Niels Jacubiak Andersen Distortion II is an experimental research project developed to create a bending acoustic surface (Krydsrum); Magnus Gustafson and Patric Gustafson (Akustikmiljo)); Copenhagen, Denmark, 2011 able to create visual and acoustic e ects within an open-plan space (Figure 19). The temporary structure Distortion II is an experimental research project developed to create a bending acoustic surface is composed by a folded surface, made of composite plates arranged in a series of trihedral corners able to create visual and acoustic effects within an open-plan space (Figure 19). The temporary with di erent dimensions and orientations. Four di erent digital production techniques were used structure is composed by a folded surface, made of composite plates arranged in a series of trihedral in the installation, i.e., laser cutting, knife cutting, CNC routing and metal bending, and fabrication corners with different dimensions and orientations. Four different digital production techniques files were generated by a custom tool. The installation explores the potentials of acoustic subspaces were used in the installation, i.e., laser cutting, knife cutting, CNC routing and metal bending, and (see also MPAS project) and creates a sound-amplified area and a sound-dampened zone. To this fabrication files were generated by a custom tool. The installation explores the potentials of acoustic aim, the APBD approach was applied to define the materials, the level of enclosure of the structure subspaces (see also MPAS project) and creates a sound-amplified area and a sound-dampened zone. and the geometry of the panels to control sound reflections. The acoustic parameters used to define To this aim, the APBD approach was applied to define the materials, the level of enclosure of the and measure the inhomogeneous acoustic space surrounding the installation were reverberation time, structure and the geometry of the panels to control sound reflections. The acoustic parameters used early decay time, sound strength and an experimental parameter (STV IA-di ) [117,118]. Two design to define and measure the inhomogeneous acoustic space surrounding the installation were workflows were used in the development of the project: in the first Odeon was used to run the reverberation time, early decay time, sound strength and an experimental parameter (STV IA-diff) [117,118]. Two design workflows were used in the development of the project: in the first Odeon was used to run the acoustic simulation, while in the second the acoustic analyses were directly run within the modeling environment using a custom ray-tracing tool, to provide instantaneous performance feedback for the optimization process. The latter workflow was only used in conceptual phases, while Acoustics 2020, 2 269 acoustic simulation, while in the second the acoustic analyses were directly run within the modeling environment using a custom ray-tracing tool, to provide instantaneous performance feedback for Acoustics 2020, 3 FOR PEER REVIEW 24 the optimization process. The latter workflow was only used in conceptual phases, while Odeon was extensively used in subsequent ones to accurately calculate the di erent acoustic parameters Odeon was extensively used in subsequent ones to accurately calculate the different acoustic considered. The plates that compose the installation feature opposite acoustic properties on their parameters considered. The plates that compose the installation feature opposite acoustic properties sides, being composed by a layer of sound absorbing material, a structural MDF panel and a layer on their sides, being composed by a layer of sound absorbing material, a structural MDF panel and a with a sound-reflective aluminum face. The arrangement and materials of the plates of the trihedral layer with a sound-reflective aluminum face. The arrangement and materials of the plates of the corners were optimized through an iterative routine to generate the two acoustic subzones. In the trihedral corners were optimized through an iterative routine to generate the two acoustic subzones. sound-amplified zone, the plates sides feature sound reflective properties and are arranged in order to In the sound-amplified zone, the plates sides feature sound reflective properties and are arranged in create focusing, while on the sound-dampened area, the faces of the plates feature sound absorptive order to create focusing, while on the sound-dampened area, the faces of the plates feature sound properties and their configuration promotes sound di usion [117,119]. absorptive properties and their configuration promotes sound diffusion [117,119]. Figure 19. Distortion II. Image courtesy © Anders Ingvartsen. Figure 19. Distortion II. Image courtesy © Anders Ingvartsen. 3. Discussion 3. Discussion The information regarding the design processes of the case studies is summarized in Figure 20, The information regarding the design processes of the case studies is summarized in Figure 20, where the case studies within the categories “music venues” and “other spaces” have been further where the case studies within the categories “music venues” and “other spaces” have been further classified in accordance to their architectural typologies. The table gathers information regarding the classified in accordance to their architectural typologies. The table gathers information regarding the primary functions, the design features developed with APBD, as well as ragarding the procedures and primary functions, the design features developed with APBD, as well as ragarding the procedures tools used in the development of the projects. and tools used in the development of the projects. Acoustics 2020, 2 270 Acoustics 2020, 3 FOR PEER REVIEW 25 Figure 20. The table o ers an overview of the projects, gathering relevant data on their architectural Figure 20. The table offers an overview of the projects, gathering relevant data on their architectural features and on the design development. features and on the design development. 3.1. Architecture and APBD 3.1. Architecture and APBD The collection of case studies shows a great degree of variation with respect to their functions The collection of case studies shows a great degree of variation with respect to their functions and profiles: from world-renowned concert halls to more ordinary architectures, research projects and and profiles: from world-renowned concert halls to more ordinary architectures, research projects artistic installations. and artistic installations. Most of case studies are major projects, such as concert halls venues, developed by renowned Most of case studies are major projects, such as concert halls venues, developed by renowned architectural firms and acoustic consulting groups, or were developed as research projects. In the first architectural firms and acoustic consulting groups, or were developed as research projects. In the first case, the resources and specialized expertise that are often available to major architectural firms, along case, the resources and specialized expertise that are often available to major architectural firms, with the reliance on external consultants, enable an innovative approach such as APBD to be e ectively along with the reliance on external consultants, enable an innovative approach such as APBD to be applied. However, such resources are generally not available in more ordinary projects, especially effectively applied. However, such resources are generally not available in more ordinary projects, when the architectural firms involved have no technical expertise on parametric modeling, acoustics especially when the architectural firms involved have no technical expertise on parametric modeling, and programming, as it is often the case. This result suggests that this procedure requires specialized acoustics and programming, as it is often the case. This result suggests that this procedure requires expertise and resources, which are not commonly available for ordinary architectural projects. specialized expertise and resources, which are not commonly available for ordinary architectural Most projects are spaces meant to host music performance (16 projects out of 19), while only a projects. small fraction of the projects is developed for other purposes (e.g., artistic installation, meeting room and multipurpose space). This suggest that the application of APBD is in line with the general trend of Acoustics 2020, 2 271 including acoustic concerns mainly in the development of spaces intended for music performances. However, certain projects, such as FabPod, Resonant Chamber and the Courtyard Enclosure of the Smithsonian Institution, shows the application of APBD for spaces intended for a wider variety of purposes. Across the collection, APBD has been applied to either major or minor architectural features of the design, ranging from reflectors and pattern textures in concert halls, to the overall shape of smaller architectures, such as acoustic shells or artistic installations. In the design of concert halls, the main structure of the venue is generally based on well-known typologies (e.g., shoe-box, vineyard, etc.), while APBD is applied to reflective surfaces or di usive pattern. In smaller intervention, such as pavilion and acoustic shells, APBD has been applied also to entirely shape the structures, often combining other goals, such as fabrication criteria. This highlights that PBD approach is often paired with a more conventional approach in large projects to better combine the large number of requirements, which need to be considered. 3.2. Digital Workflows in APBD APBD is normally applied due to the combined use of parametric modeling and acoustic performance simulation tools. Moreover, optimization tools can be exploited to automate the search of the most favorable solutions with respect to the target performance goals. The parametric modeling tool that was used in the great majority of the considered projects is Grasshopper [20] for Rhinoceros [21]. Acoustic analyses were mainly run using custom tools based on geometrical acoustics, while the commercial package that was used the most is Odeon [38]. In many cases, optimization tools based on evolutionary algorithms, such as Galapagos [24] and Octopus [25], have been utilized to support the design process. Parametric modeling eases the design optimization process, by allowing one to easily modify the design by controlling the model parameters. Grasshopper is one of the most commonly used parametric modeling tools. It is a graphical algorithm editor integrated in Rhinoceros, which is a commercial modeling tool widely employed in architectural practice. Grasshopper enables one to generate parametric models of complex geometries on the basis of algorithms set by the designer. Grasshopper does not require any programming knowledge and is therefore employed by designers with relative ease. Currently, a wide number of acoustic simulation tools, such as Odeon, CATT-Acoustic, etc., are available, allowing professionals to quickly perform simulations based on geometrical acoustic methods. Odeon is the commercial package that was more widely employed in the collected case studies. Acoustic simulation tools require a solid acoustic knowledge base to correctly set up the simulation and interpret its results. In most cases, the acoustic knowledge of architectural professionals is not adequate to correctly employ these systems, making the reliance on external acoustic consultants unavoidable. Another limitation is due to the lack of integration among simulation and modeling tools, which are generally stand-alone applications, and the limited interoperability resulting from the specific formats or geometrical models required to run the acoustic simulation. Some tools, such as the SketchUp plugin of Odeon [120], ease the file exchange between the modeling and simulation environments. However, the generation of specific model for acoustic analyses is often mandatory to meet the requirements of the simulation tools (e.g., geometrical simplification, watertight model and layer division by materials). Therefore, architectural design and acoustic performance analyses need to be run into two separated environments on specific virtual models, resulting in a time-consuming process, which often limits the number of model exchanges among professionals. As a result, design optimization in early design phases can be dicult to achieve from the feedback provided by these tools, which are more commonly used in late design phases for verification purposes, as shown in many case studies. A noteworthy exception in this frame is Pachyderm Acoustics [40], an open-source acoustic simulation tool integrated in Rhinoceros/Grasshopper, which was used in the development of FabPod. Acoustics 2020, 2 272 In many case studies custom tools were employed to avoid the issues resulting from the poor level of interoperability and to perform specific analyses. For instance, the use of custom tool has been reported in 16 out of 19 case studies. Such tools are generally used in early design phases to provide quick estimations of the acoustic performances directly in the modeling environment. Currently, di erent modeling platforms o er the possibility to the users to create custom programs (e.g., Rhinoscript, Grasshopper, Python, etc.) within their environment, widening the possibilities o ered by the regular preset functionalities. In most cases, custom tools have been used in early design phases to run simplified performance analyses, easily visualize the results and optimize the design proposal accordingly. By clarifying the relation between acoustic and architectural design, these tools support an e ective collaboration between architect and acousticians, and possibly the other technicians involved, enabling one to integrate di erent goals in the design proposal. Custom acoustic simulation tools are generally based on geometrical acoustic technique and apply ray-tracing or image-source methods. The performance feedback obtained, although simplified, is considered accurate enough to orient the design decision in early design phases. In many cases, more accurate analyses were run in late design phases with commercial acoustic simulation tools to further validate the results. Following a di erent approach, custom tools can be used to run sophisticated acoustic analyses, such as wave-based ones, which at the time of writing are not included in any commercial acoustic simulation package. In wave-based simulations, the wave behavior of sound phenomena, which are normally neglected in geometrical acoustic simulations, can be accurately simulated in 2D environments. For instance, in the development of FabPod, wave-based acoustic simulations were used to assess the scattering performance of the surfaces, which could not be accounted with geometrical acoustic techniques. Despite the wide range of possibilities o ered by custom tools, the programming skills and acoustic knowledge required in their development and application are normally not available to architectural firms. However, currently the availability of several online coding courses and of platforms such as ACOUCOU [121], which o ers free education materials on acoustics, may help to fill the gap. Furthermore, the introduction of PBD approach in architectural education would help students to become more familiar with building performance and simulation tools. Some of the case studies analyzed (e.g., ReS 6.0, Aalborg Acoustic Pavilions, MPAS project and Distortion II) were developed in an educational framework, and students were actively involved through summer schools and workshop; previous educational experiences with the PBD approach have been also documented in [16,17]. The design optimization can be performed either manually, for subsequent iterations by the operator, or in an automated matter. In the latter case, the parametric model is automatedly optimized on the basis of performance feedback until one or more satisfying solutions are achieved, resulting in a quick and ecient process. The support of automated processes has been reported in the development of most case studies (11 out of 19). The optimization tools that were used in the case studies analyzed are Galapagos and Octopus, which are based on evolutionary algorithms, and are directly integrated in Grasshopper for Rhinoceros. Such tools enable one to run either single objective or multiobjective optimization of parametric models defined in Grasshopper, based on target requirements and variation space set by the user. The performance feedbacks needed to set up the optimization process are generally obtained from the custom acoustic simulation tool integrated in the modeling environment. The design proposal can be optimized since early design phases based on the simplified performance feedbacks from the custom acoustic simulation tools, while more sophisticated simulation systems, such as Odeon, can be employed in late design phases when most design features have been already defined. These tools can be used to verify the performance of the preselected design proposals and provide the designers with detailed suggestions for further design improvements. For instance, commercial packages were used in late design phases to validation purposes in the Philharmonie de Paris, in the music venues in Fuzhou and in ReS 6.0. Acoustics 2020, 2 273 4. Conclusions As the impact of acoustic performances on human well-being are being acknowledged, acoustic concerns are expected to be increasingly integrated in the design of spaces with a variety of functions. In common practice, acoustic consultants are rarely involved since early design phases, and acoustic optimization and architectural design tend to be rather independent processes. In this frame, the application of performance-based design in acoustics seems very promising to optimize design proposals in light of performance feedbacks obtained from acoustic simulation tools. However, the method finds little application in current architectural practice, and is mainly restricted to notable architectures and research projects. A set of case studies developed with APBD has been collected in the attempt to shed some light on the state of the art of the application of the method in current architectural practice, evidence the design strategies followed and suggest some possible fields of improvement to further encourage its application. The development of integrated platforms that combine acoustic analyses and architectural modeling, the increased interoperability among modeling and simulation tools, would ease performance analyses in early design phases, and will allow for an e ective collaboration among architectural and acoustic specialists. The enhancement of acoustic and coding skills of designers, which can be promoted by the provision of specialized teaching platforms, would support the development and application of custom tools to run simplified analyses in the modeling environment during early design phases, hopefully encouraging the application of APBD in practice. Author Contributions: Conceptualization, L.S.; methodology, E.B., L.S. and A.A.; investigation, E.B.; resources, L.S. and A.A.; data curation, E.B.; writing—original draft preparation, E.B.; writing—review and editing, L.S. and A.A.; visualization, E.B.; supervision, L.S. and A.A. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors would like to thank the professionals that provided useful information to the authors on the design processes, and the copyright owners of the photographs that granted the permission to use the images in this work. Conflicts of Interest: The authors declare no conflict of interest. The information given on each project has been carefully obtained from publications and information available online. Any possible inaccurate information should be considered unintended and can be reported to the authors. References 1. Shi, X. Performance-based and performance-driven architectural design and optimization. Front. Arch. Civ. Eng. China 2010, 4, 512–518. [CrossRef] 2. Shi, X.; Yang, W. Performance-driven architectural design and optimization technique from a perspective of architects. Autom. Constr. 2013, 32, 125–135. [CrossRef] 3. Turrin, M.; Von Buelow, P.; Stou s, R. Design explorations of performance driven geometry in architectural design using parametric modeling and genetic algorithms. Adv. Eng. Inform. 2011, 25, 656–675. [CrossRef] 4. Grobman, Y.J.; Ron, R. Digital Form Finding: Generative use of simulation processes by architects in the early stages of the design process. In Proceedings of the 29th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Ljubljana, Slovenia, 21–24 Semptember 2011; pp. 107–115. [CrossRef] 5. Chong, Y.T.; Chen, C.H.; Leong, K.F. A heuristic-based approach to conceptual design. Res. Eng. Des. 2009, 20, 97–116. [CrossRef] 6. Wang, J. Improved engineering design concept selection using fuzzy sets. Int. J. Comput. Integr. Manuf. 2002, 15, 18–27. [CrossRef] 7. Méndez Echenagucia, T.; Capozzoli, A.; Cascone, Y.; Sassone, M. The early design stage of a building envelope: Multi-objective search through heating, cooling and lighting energy performance analysis. Appl. Energy 2015, 154, 577–591. [CrossRef] Acoustics 2020, 2 274 8. Lu, S.; Yan, X.; Li, J.; Xu, W. The influence of shape design on the acoustic performance of concert halls from the viewpoint of acoustic potential of shapes. Acta Acust. United Acust. 2016, 102, 1027–1044. [CrossRef] 9. Paulson, B.C., Jr. Designing to Reduce Construction Costs. J. Constr. Div. 1976, 102, 587–592. [CrossRef] 10. Marble, S. Digital Workflows in Architecture: Design–Assembly–Industry; Birkhauser: Basel, Switzerland, 2012. 11. Méndez Echenagucia, T. Computational Search in Architectural Design. Ph.D. Thesis, Polytechnic University of Turin, Turin, Italy, 2013. 12. Reinhardt, D.; Martens, W.L.; Miranda, L. Acoustic Consequences of Performative Structures—Modelling dependencies between spatial formation and acoustic behaviour. In Proceedings of the 30th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Prague, Czech Republic, 12–14 September 2012; pp. 577–586. 13. Becker, R. Fundamentals of performance-based building design. Build. Simul. 2008, 1, 356–371. [CrossRef] 14. Hensel, M. Performance-Oriented Architecture: Rethinking Architectural Design and the Built Environment; John Wiley & Sons: Hoboken, NJ, USA, 2013. [CrossRef] 15. Kolarevic, B.; Malkawi, A. Performative Architecture: Beyond Instrumentality; Routledge: Abingdon-on-Thames, UK, 2005. [CrossRef] 16. Holzer, D. Design exploration supported by digital tool ecologies. Autom. Constr. 2016, 72, 3–8. [CrossRef] 17. Jensen, M.B. Robotic Fabrication of Acoustic Geometries—An explorative and creative design process within an educational context. ArchiDOCT 2019, 6, 34–45. 18. Oxman, R. Performance-Based Design: Current Practices and Research Issues. Int. J. Arch. Comput. 2008, 6, 1–17. [CrossRef] 19. Oxman, R. Theory and design in the first digital age. Des. Stud. 2006, 27, 229–265. [CrossRef] 20. Rutten, D. Grasshopper. Available online: http://www.grasshopper3d.com/ (accessed on 18 March 2020). 21. Rhinoceros. Available online: http://www.rhino3d.com/ (accessed on 18 March 2020). 22. GenerativeComponents. Available online: https://www.bentley.com/en/products/product-line/modeling- and-visualization-software/generativecomponents (accessed on 18 March 2020). 23. Flager, F.; Haymaker, J. A comparison of multidisciplinary design, analysis and optimization processes in the building construction and aerospace industries. In Proceedings of the 24th W78 Conference, Maribor, Slovenia, 27–29 June 2007; pp. 625–630. [CrossRef] 24. Rutten, D. Galapagos. Available online: http://www.grasshopper3d.com/group/galapagos (accessed on 18 March 2020). 25. Vierlinger, R. Octopus. Available online: http://www.food4rhino.com/app/octopus (accessed on 18 March 2020). 26. Tang, M.; Anderson, J.; Aksamija, A.; Hodge, M. Performace-based Generative Design: An investigation of the parametric nature of architecture. In Proceedings of the 100th Association of Collegiate Schools of Architecture (ACSA) Annual Meeting, Boston, MA, USA, 1–4 March 2012; Volume 2, pp. 1–8. 27. Bassuet, A.; Rife, D.; Dellatorre, L. Computational and Optimization Design in Geometric Acoustics. Build. Acoust. 2014, 21, 75–85. [CrossRef] 28. Takenaka, T.; Okabe, A. A Computational Method for Integrating Parametric Origami Design and Acoustic Engineering. Comput. Perform. 2013, 2, 289–296. 29. World Health Organization. Environmental Noise Guidelines for the European Region. 2018. Available online: http://www.euro.who.int/en/publications/abstracts/environmental-noise-guidelines-for- the-european-region-2018 (accessed on 18 March 2020). 30. Di Blasio, S.; Shtrepi, L.; Puglisi, G.E.; Astolfi, A. A Cross-Sectional Survey on the Impact of Irrelevant Speech Noise on Annoyance, Mental Health and Well-being, Performance and Occupants’ Behavior in Shared and Open-Plan Oces. Int. J. Environ. Res. Public Health 2019, 16, 280. [CrossRef] 31. Reinten, J.; Braat-Eggen, P.E.; Hornikx, M.; Kort, H.S.M.; Kohlrausch, A. The indoor sound environment and human task performance: A literature review on the role of room acoustics. Build. Environ. 2017, 123, 315–332. [CrossRef] 32. Badino, E.; Manca, R.; Shtrepi, L.; Calleri, C.; Astolfi, A. E ect of façade shape and acoustic cladding on reduction of leisure noise levels in a street canyon. Build. Environ. 2019, 157, 242–256. [CrossRef] 33. ISO 3382-1:2009. Acoustics—Measurement of room acoustic parameters. Part 1: Performance spaces. Int. Organ. Stand. 2009. Available online: https://www.iso.org/standard/40979.html (accessed on 18 March 2020). Acoustics 2020, 2 275 34. ISO 3382-2:2009. Acoustics—Measurement of room acoustics parameters. Part 2: Reverberation time in ordinary rooms. Int. Organ. Stand. 2009. Available online: https://www.iso.org/standard/36201.html (accessed on 18 March 2020). 35. Shtrepi, L.; Astolfi, A.; D’Antonio, G.; Guski, M. Objective and perceptual evaluation of distance-dependent scattered sound e ects in a small variable-acoustics hall. J. Acoust. Soc. Am. 2016, 140, 3651–3662. [CrossRef] 36. Bo, E.; Astolfi, A.; Pellegrino, A.; Pelegrin-Garcia, D.; Puglisi, G.E.; Shtrepi, L.; Rychtarikova, M. The modern use of ancient theatres related to acoustic and lighting requirements: Stage design guidelines for the Greek theatre of Syracuse. Energy Build. 2015, 95, 106–115. [CrossRef] 37. Cox, T.J.; D’Antonio, P. Acoustic Absorbers and Di users: Theory, Design and Application; Spon Press: London, UK, 2004. 38. Odeon. Available online: http://odeon.dk/ (accessed on 18 March 2020). 39. CATT-Acoustic. Available online: https://www.catt.se/ (accessed on 18 March 2020). 40. Van der Harten, A. Pachyderm Acoustics. Available online: http://www.perspectivesketch.com/pachyderm/ (accessed on 18 March 2020). 41. Lokki, T.; Southern, A.; Siltanen, S.; Savioja, L. Acoustics of epidaurus—Studies with room acoustics modelling methods. Acta Acust. United Acust. 2013, 99, 40–47. [CrossRef] 42. Shtrepi, L.; Hamilton, B.; Astolfi, A.; Masoero, M. Preliminary results of scattering surface modeling and perceptual aspects in wave-based acoustic simulations. In Proceedings of the 23rd International Congress on Acoustics, Aachen, Germany, 9–13 September 2019; pp. 5990–5993. [CrossRef] 43. Orazio, D.D.; Fratoni, G.; Rovigatti, A.; Hamilton, B. Numerical simulations of Italian opera houses using geometrical and wave-based acoustics methods. In Proceedings of the 23rd International Congress on Acoustics, Aachen, Germany, 9–13 September 2019; pp. 5994–5996. 44. Lu, S.; Yan, X.; Xu, W.; Chen, Y.; Liu, J. Improving auditorium designs with rapid feedback by integrating parametric models and acoustic simulation. Build. Simul. 2016, 9, 235–250. [CrossRef] 45. Negendahl, K. Building performance simulation in the early design stage: An introduction to integrated dynamic models. Autom. Constr. 2015, 54, 39–53. [CrossRef] 46. Mirra, G.; Pignatelli, E.; Di Rosario, S. An automated design methodology for acoustic shells in outdoor concerts. In Proceedings of the Euronoise, Crete, Greece, 27–31 May 2018; pp. 2123–2130. 47. Peters, B. Parametric Acoustic Surfaces. In reForm(), Proceedings of the Association for Computer Aided Design in Architecture 2009 Conference, Chicago, USA, 22–25 Octorber 2009; Sterk, T.D.E., Loveridge, R., Pancoast, D., Eds.; pp. 174–181. Available online: https://adk.elsevierpure.com/en/publications/parametric-acoustic-surfaces (accessed on 18 March 2020). 48. Peters, B. Integrating Acoustic Analysis in the Architectural Design Process using Parametric Modeling; Forum Acusticum: Aalborg, Denmark, 2011; pp. 1589–1594. 49. Wortmann, T.; Tunçer, B. Di erentiating parametric design: Digital workflows in contemporary architecture and construction. Des. Stud. 2017, 52, 173–197. [CrossRef] 50. Scopus. Available online: https://www.scopus.com (accessed on 18 March 2020). 51. Research Gate. Available online: https://www.researchgate.net/ (accessed on 18 March 2020). 52. Alias System Corporation; Autodesk, Autodesk Maya. Available online: https://www.autodesk.com/ products/maya/overview (accessed on 18 March 2020). 53. Day, C.; Marshall, H.; Scelo, T.; Valentine, J.; Exton, P. The Philharmonie de Paris—Acoustic design and commissioning. Proceedings of Acoustics 2016: The Second Australasian Acoustical Societies Conference, Brisbane, Australia, 9–11 November 2016; pp. 1–15. 54. McGar, J. The Acoustic Feats of the World’s Costliest Concert Hall. 2015. Available online: https: //sourceable.net/acoustic-feats-worlds-costliest-concert-hall/ (accessed on 18 March 2020). 55. Philharmonie de Paris. Available online: http://www.nagata.co.jp/e_sakuhin/factsheets/PdP.pdf (accessed on 18 March 2020). 56. Marshall, H. Implementing the acoustical concept for the Philharmonie de Paris, Grande Salle. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; Volume 37, Pt 3, pp. 118–127. 57. Kahle, E.; Wulfrank, T.; Jurkiewicz, Y.; Faillet, N. Philharmonie de Paris—The Acoustic Brief. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; Volume 37, Pt 3, pp. 105–110. Acoustics 2020, 2 276 58. Scelo, T. Integration of acoustics in parametric architectural design. Acoust. Aust. 2015, 43, 59–67. [CrossRef] 59. Philharmonie de Paris—Information Sheet. Available online: http://www.kahleacoustics.com/en/ref/ philharmonie.html# (accessed on 18 March 2020). 60. Khan, N. An Algorithm Designed a Hamburg Concert Hall’s Interior, Creating the Ideal Acoustic Experience. 2017. Available online: https://qz.com/894929/an-algorithm-designed-a-hamburg-concert-halls-interior- creating-the-ideal-acoustic-experience/ (accessed on 18 March 2020). 61. Elbphilharmonie Hamburg Grosser Saal. Available online: http://www.nagata.co.jp/e_sakuhin/factsheets/ Elbphilharmonie.pdf (accessed on 18 March 2020). 62. Stinson, E. What Happens When Algorithms Design a Concert Hall? The Stunning Elbphilharmonie. 2017. Available online: https://www.wired.com/2017/01/happens-algorithms-design-concert-hall-stunning- elbphilharmonie/ (accessed on 18 March 2020). 63. Oguchi, K. Highlights of Room Acoustics and Sound Isolation Design. 2017. Available online: http: //www.nagata.co.jp/e_news/news1702-e.html (accessed on 18 March 2020). 64. Architectural Details: Herzog & de Meuron’s Spectacular Elbphilharmonie. 2016. Available online: https: //architizer.com/blog/architectural-details-herzog-de-meuron-elbphilharmonie/ (accessed on 18 March 2020). 65. Mommertz, E.; Kahle, E. The Bochum Concert Hall—The challenge of small concert halls for large orchestras on low budget. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Cardiff, UK, 4–6 October 2018; Volume 40, Pt 1, pp. 174–181. 66. Anneliese Brost Musikforum Ruhr. Available online: https://www.architonic.com/en/project/bez-kock- architekten-anneliese-brost-musikforum-ruhr/5106249 (accessed on 18 March 2020). 67. Musikzentrum Bochum—Information Sheet. Available online: http://www.khale.be/en/ref/bochum.html# (accessed on 18 March 2020). 68. Nishiyama, Y. Miura folding: Applying Origami to space exploration. Int. J. Pure Appl. Math. 2012, 79, 269–279. 69. Ureshino Cultural Center. 2014. Available online: http://www.suep.jp/Ureshino_cultural_center/text_inE. html (accessed on 18 March 2020). 70. @Last Software; Google, SketchUp. Available online: https://www.sketchup.com/ (accessed on 18 March 2020). 71. Autodesk Revit. Available online: http://www.autodesk.com/revit (accessed on 18 March 2020). 72. Garber, R. Workflows: Expanding Architecture’s Territory in the Design and Delivery of Buildings; John Wiley & Sons: Hoboken, NJ, USA, 2017. 73. Theatroacoustic System for University of Iowa Concert Hall. Available online: https://lmnarchitects.com/ case-study/theatroacoustic-system-concert-hall (accessed on 18 March 2020). 74. Cornachio, J. Behind the Building: Voxman Music Building by LMN Architects. Available online: https: //architizer.com/blog/practice/materials/behind-voxman-music-building/ (accessed on 18 March 2020). 75. Jurkiewicz, Y.; Wulfrank, T.; Kahle, E. Architectural shape and early acoustic eciency in concert halls (L). J. Acoust. Soc. Am. 2012, 132, 1253–1256. [CrossRef] 76. Jurkiewicz, Y.; Moller, H.; Wulfrank, T.; Wang, J.; Kahle, E. Acoustic Optimization of Curved Architecture in Practice: The New Straight Cultural Arts Center in Fuzhou. In Proceedings of the International Symposium on Room Acoustics, Amsterdam, Netherlands, 15–17 September 2019; pp. 401–408. 77. Wulfrank, T.; Jurkiewicz, Y.; Kahle, E. Design-Focused Acoustic Analysis of Curved Geometries using a Di erential Raytracing Technique. Build. Acoust. 2014, 21, 87–96. [CrossRef] 78. García Gòmez, J.Ó.; Kahle, E.; Wulfrank, T. Shaping concert halls. In Proceedings of the EuroRegio, Porto, Portugal, 13–15 June 2016. 79. CATIA. Available online: http://www.3ds.com/products-services/catia/ (accessed on 18 March 2020). 80. Square One Research; Autodesk, Ecotect Analysis. Available online: https://www.autodesk.com/education/ free-software/ecotect-analysis (accessed on 18 March 2020). 81. Minutillo, J. When the Whole Is Greater Than the Sum of Its Parts. 2009. Available online: https://continuingeducation.bnpmedia.com/courses/areditorial/when-the-whole-is-greater-than- the-sum-of-its-parts/ (accessed on 18 March 2020). 82. The Conga Room/Belzberg Architects. 2011. Available online: http://www.archdaily.com/160584/the-conga- room-belzberg-architects (accessed on 18 March 2020). 83. Conga Room at LA Live. Available online: http://belzbergarchitects.com/project/conga-room/ (accessed on 18 March 2020). Acoustics 2020, 2 277 84. The Conga Room, Los Angeles. Available online: http://www.designcurial.com/projects/the_conga_room_ los_angeles (accessed on 18 March 2020). 85. Dynamo. Available online: http://dynamobim.org/ (accessed on 18 March 2020). 86. Fang, D. Shells for the Senses: The Multidisciplinary Success of Stage by the Sea. 2016. Available online: https://formfindinglab.wordpress.com/2016/09/21/shells-for-the-senses-the-multidisciplinary- success-of-stage-by-the-sea/ (accessed on 18 March 2020). 87. Flanagan, J. Acoustic Shells. Shotcrete 2015, 17, 16–19. 88. Griths, A. Shell-Shaped Shelter by Flanagan Lawrence Built on Littlehampton Seafront. 2014. Available online: https://www.dezeen.com/2014/07/22/flanagan-lawrence-acoustic-shells-shelter-stage-littlehampton/ (accessed on 18 March 2020). 89. Flanagan Lawrence—Acoustic Shells. Available online: https://theplan.it/eng/webzine/the-plan-award-2015/ acoustic-shells#sthash.XmPPnnkv.dpbs (accessed on 18 March 2020). 90. Acoustic Shells. Available online: http://flanaganlawrence.com/project/acoustic-shells/ (accessed on 18 March 2020). 91. Soundforms. Available online: https://www.flanaganlawrence.com/soundforms (accessed on 18 March 2020). 92. The Park’s Bandstand—A Built Environment Story. Available online: http://www.beyond2012.org.uk/ sounforms-the-parks-bandstand/ (accessed on 18 March 2020). 93. Bavister, P. Soundforms. (n.d.) 405–421. Available online: https://www.academia.edu/6385238/The_design_ development_and_fabrication_of_a_11_scale_mobile_acoustic_performance_shell_prototype (accessed on 28 April 2020). 94. Boning, W.; Acoustics, A.; Bassuet, A.; Rise, T.; Shell, G. A Room Without Walls: Optimizing an Outdoor Music Shell To Maintain Views and Maximize Reflections. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; pp. 332–341. 95. Foged, I.W.; Pasold, A.; Brath, M. Acoustic Environments: Applying Evolutionary Algorithms for Sound Based Morphogenesis. In Proceedings of the 30th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Prague, Czech Republic, 12–14 September 2012; pp. 347–353. 96. Furuto, A. Acoustic Environments/AREA and Electrotexture Lab. 2011. Available online: https://www. archdaily.com/170078/acoustic-environments-area-and-electrotexture-lab (accessed on 18 March 2020). 97. Foged, I.W.; Pasold, A.; Jensen, M.B. Evolution of an Instrumental Architecture. In Proceedings of the 32nd Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Newcastle upon Tyne, UK, 10–12 Semptember 2014; pp. 365–372. 98. Piker, D. Kangaroo. Available online: http://kangaroo3d.com/ (accessed on 18 March 2020). 99. Resonant Chamber. Available online: http://www.rvtr.com/projects/resonant-chamber (accessed on 18 March 2020). 100. Anderson, L. Origami in Stereo: Welcome to the Sound Cloud! Available online: https://architizer.com/blog/ resonant-chamber-rvtr/ (accessed on 18 March 2020). 101. Filipetti, J. Rvtr: Resonant Chamber Origami Architectural Acoustic Panels. Available online: http://www. designboom.com/technology/rvtr-resonant-chamber-origami-architectural-acoustic-panels/ (accessed on 18 March 2020). 102. Grozdanic, L. Resonant Chamber Is An Acoustically Responsive Envelope. Available online: http://www.evolo. us/architecture/resonant-chamber-is-an-acoustically-responsive-envelope/ (accessed on 18 March 2020). 103. Thün, G.; Velikov, K.; Ripley, C.; Sauvé, L.; McGee, W. Soundspheres: Resonant Chamber. Leonardo 2012, 45, 348–357. [CrossRef] 104. Peters, B. Acoustic Performance as a Design Driver: Sound Simulation and Parametric Modeling using SmartGeometry. Int. J. Arch. Comput. 2011, 8, 337–358. [CrossRef] 105. Peters, B. The Smithsonian Courtyard Enclosure: A case-study of digital design processes. Acadia 2007, 2007, 74–83. 106. Smithsonian Institution. Available online: http://www.bradypeters.com/smithsonian.html (accessed on 18 March 2020). 107. Smithsonian Selects Norman Foster to Design New Atrium for Historic Home of two Museum. Available online: https://www.fosterandpartners.com/news/archive/2004/03/smithsonian-selects-norman-foster-to- design-new-atrium-for-historic-home-of-two-museums/ (accessed on 18 March 2020). Acoustics 2020, 2 278 108. Williams, N.; Burry, J.; Davis, D.; Peters, B.; Pena De Leon, A.; Burry, M. FabPod: Designing with temporal flexibility & relationships to mass-customisation. Autom. Constr. 2015, 51, 124–131. [CrossRef] 109. Williams, N.; Davis, D.; Peters, B.; Pena de Leon, A.; Burry, J.; Burry, M. Fabpod: An open design-to-fabrication system. In Proceedings of the 18th International Conference on Computer-Aided Architectural Design Research in Asia (CAADRIA 2013), Singapore, 2013; pp. 251–260. 110. Burry, J.; Williams, N.; Cherrey, J.; Peters, B. Fabpod: Universal Digital Workflow, Local Prototype Materialization. In Proceedings of the 15th International Conference on Computer-Aided Architectural Design Futures, Shanghai, China, 3–5 July 2013; pp. 176–186. 111. Burry, M. FabPod. Available online: https://mcburry.net/fabpod/ (accessed on 18 March 2020). 112. Davis, D. FabPod. Available online: https://www.danieldavis.com/fabpod/ (accessed on 18 March 2020). 113. Peters, B. Integrating acoustic simulation in architectural design workflows: The FabPod meeting room prototype. Simulation 2015, 91, 787–808. [CrossRef] 114. Wong, K. Shaped by Number. 2010. Available online: http://www.cgw.com/Publications/CGW/2010/Volume- 33-Issue-9-October-2010-/Shaped-by-Number.aspx (accessed on 18 March 2020). 115. Peters, B. Complex Surfaces—Sound and Space Defining Surfaces for Architecture. Available online: https: //kadk.dk/case/complex-surfaces-sound-and-space-defining-surfaces-architecture (accessed on 18 March 2020). 116. Manufacturing Parametric Acoustic Surfaces. Available online: http://www.bradypeters.com/smartgeometry- 2010.html (accessed on 18 March 2020). 117. Peters, B.; Tamke, M.; Nielsen, S.A.; Vestbjerg Andersen, S.; Haase, M. Responsive Acoustic Surfaces, in: Respect. In Proceedings of the 29th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Ljubljana, Slovenia, 21–24 Semptember 2011; pp. 819–828. 118. Pelegrín-García, D. Comment on “Increase in voice level and speaker comfort in lecture rooms” [J. Acoust. Soc. Am. 125, 2072–2082 (2009)] (L). J. Acoust. Soc. Am. 2011, 129, 1161–1164. [CrossRef] 119. Project Distortion II. Available online: http://www.bradypeters.com/project-distortion-ii.html (accessed on 18 March 2020). 120. SU2Odeon Plugin for SketchUp. Available online: https://odeon.dk/downloads/su2odeon/ (accessed on 18 March 2020). 121. ACOUCOU. Available online: https://acoucou.org/ (accessed on 18 March 2020). © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acoustics Multidisciplinary Digital Publishing Institute

Acoustic Performance-Based Design: A Brief Overview of the Opportunities and Limits in Current Practice

Acoustics , Volume 2 (2) – May 1, 2020

Loading next page...
 
/lp/multidisciplinary-digital-publishing-institute/acoustic-performance-based-design-a-brief-overview-of-the-IZ0ppE8mZr
Publisher
Multidisciplinary Digital Publishing Institute
Copyright
© 1996-2021 MDPI (Basel, Switzerland) unless otherwise stated Disclaimer The statements, opinions and data contained in the journals are solely those of the individual authors and contributors and not of the publisher and the editor(s). MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Terms and Conditions Privacy Policy
ISSN
2624-599X
DOI
10.3390/acoustics2020016
Publisher site
See Article on Publisher Site

Abstract

acoustics Review Acoustic Performance-Based Design: A Brief Overview of the Opportunities and Limits in Current Practice Elena Badino * , Louena Shtrepi and Arianna Astolfi Department of Energy, Politecnico di Torino, 10129 Torino, Italy; louena.shtrepi@polito.it (L.S.); arianna.astolfi@polito.it (A.A.) * Correspondence: elena.badino@polito.it Received: 4 April 2020; Accepted: 26 April 2020; Published: 1 May 2020 Abstract: Current development in digital design, combined with the growing awareness of the importance of building performance, had drawn attention to performance-based design (PBD) in architecture. PBD benefits both design workflow and outcome, allowing one to control the performance of the design proposal since early design phases. The paper aims to explore its current application in the acoustic field, where its potential is still little exploited in architectural practice. A set of built case studies is collected and briefly analyzed with the aim to shed some light on the state of the art of the application of acoustic performance-based design (APBD) in practice. The analysis suggests that in order to encourage the application of APBD it is needed on one side to enhance the integration and interoperability among modeling and simulation tools, and on the other side to improve the acoustic knowledge and programming skills of the architectural practitioners. Keywords: performance-based design; acoustic design; digital workflow; architectural design; design optimization; form-finding 1. Introduction 1.1. Performance-Based Design Architectural problems generally combine a great multitude of objectives, which pertain to di erent fields, such as cultural, aesthetic, economic, structural and energetic ones. As these objectives often contrast with each other, it is crucial for the design team to find the most favorable solution in overall terms. According to the classification proposed by Shi [1], architectural objectives can be divided into three categories: structural performance, performance of the physical environment—both of which can be quantified—and aesthetic and cultural performance, which relates to unquantifiable aspects. Digital simulations and measurements on scale-models allow for the evaluation of the quantifiable performances of the design proposals prior to their construction. In common practice, such tools are generally used in late design phases to verify the adherence to the performance requirements prescribed in codes, standards and laws, and evaluate the need for late design adjustments [2–4]. However, in the recent years, another approach has gained popularity, according to which performance simulations are used to drive the design process. This approach is known as performance-based design (PBD): pertinent information on one or more performance aspects is gathered since early design phases, and the proposals are iteratively optimized based on the performance feedbacks. The design process follows the loop of generation–evaluation–modification, until a solution that meets the performance goal is achieved. While not discouraging the inclusion of unquantifiable goals and Acoustics 2020, 2, 246–278; doi:10.3390/acoustics2020016 www.mdpi.com/journal/acoustics Acoustics 2020, 2 247 aesthetical considerations, pertinent information on quantifiable performances can greatly support decision-making processes in the conceptual design stages. In early design phases, designers consider a wide range of possible design solutions. Design decisions made at this stage have the greatest impact on the final performances, while late-time design adjustments can rarely compensate poor decisions made in early stages [5–8]. Moreover, design modification taken in early design phases is less costly to implement than those taken in subsequent phases [4,9]. Therefore, PBD approach benefits both design workflow and final outcome, combining a decrease in cost and time, and enhances design quality [10–12]. Indeed, with PBD designers have a greater control over the performances since early design phases and, as a result, the need for late-time design modifications or “a posteriori” measures is prevented, enhancing the overall eciency of the design process. The PBD approach emerged in the l970s and has become increasingly more appealing to architects due to the technological advancement and, in particular, to the development of performance simulation and parametric modeling tools [1,13–16]. Some educational experiences, such as those in [16,17], suggest that architectural students are increasingly being encouraged to use these tools and include performance feedback to support design decisions during the early-stage design exploration. PBD marks the paradigm shift from the traditional “form-making” to the “form-finding” approach [18]. It allows one to displace traditional know-how, enabling designers to understand the e ects of di erent design features of the proposal on performance, and to identify design scenarios that best fulfill the unique requirements of each project. The PBD method can be subdivided into two subclasses according to the way the design optimization process is conducted. In “formation models” the modifications are applied manually by the operator, while in “generative models” the design proposals are directly optimized by the computer [19]. The latter subclass is also known as “performance-driven design” [1]. Following the manual procedure, the designers control the form-generation process, allowing for the introduction of unquantifiable criteria and the technical expertise of the operator. For instance, based on performance simulation feedbacks and technical knowledge, the operator generates new design alternatives and tests them until a satisfying solution is achieved. The generation of design proposals can be eased by the use of parametric modeling tools, such as Grasshopper [20] for Rhinoceros [21] and GenerativeComponents [22]. These tools allow one to define complex geometries and to easily modify them by controlling their parameters, thus preventing the need for the operator to manually redraw each design iteration. Adequate technical skills are required in manual processes, since the success of the optimization greatly relies on the correct understanding of the relations between design features and performance [2]. However, the time and manpower required in the processes may limit the number of iterations pursued and the e ectiveness of the design optimization [1,23]. On the other hand, generative models allow one to explore a wide number of design options with a limited involvement of the operator, exploiting the functionalities of optimization tools (e.g., Galapagos [24] and Octopus [25]) [1,2,18,26]. These tools, when paired to a parametric model and a performance simulation tool, allow one to automate the search of the most performing solution within the variation space defined by the operator, while also narrowing the space of possible solutions based on the estimated performance [27]. The population of candidate solutions evolves over many generations, until a satisfactory solution is reached. This enables one to explore a wide solution space and to find potentially unconsidered design options to address the specific requirements of the project [3,28]. In automated processes it is also possible to e ectively combine di erent performance goals in multiobjective optimization procedures, which can hardly be implemented manually. In automated procedures, the involvement of the designer is generally limited to the definition of the target performance objectives and of the boundaries of the variation space within which the generative process operates, which may reflect quantifiable and unquantifiable criteria [11]. Despite these advantages, manual procedures may be preferred by professionals to allow the design exploration to be guided by their intuition and expertise gathered by working in the field. Acoustics 2020, 2 248 Manual and automated procedures are often combined in di erent ways in hybrid methods, allowing one to exploit the advantages of both approaches, based on the requirements of the design process. The PBD approach enhances the eciency of the design process by enabling to optimize the architectural proposal with respect to the performance analyzed. However, the application of PBD method is still relatively limited currently. Indeed, current architectural practice often relies on experience-based know-how and performance simulations are mainly introduced in late design phases with the aim to verify the adherence to the performance requirements. 1.2. Performance-Based Design in Acoustics The implementation of PBD in the architectural acoustics field would allow the designer to better combine acoustic performance objectives with architectural goals. Architectural design and acoustic performances are strictly linked: the emitted sound is altered by the architectural space within which it is deployed, due to sound reflection, absorption and di usion phenomena occurring over its surfaces. In common practice, however, acoustic concerns are mainly restricted to the design of spaces intended for artistic performances, such as music venues and theatres. In such spaces, the architectural environment is meant to support the sound generated by the artists, and acoustic design is critical for both audience and performers [12]. However, as the benefits of acoustic comfort on the well-being of the population are being acknowledged, acoustics concerns are introduced in a wider variety of design problems [29]. Indeed, acoustic requirements are being increasingly extended to the design of spaces not related to artistic performances, such as classrooms, workplaces and urban environments, where an appropriate acoustic performance would benefit the hosted activities and the well-being of the users [29–32]. The acoustic performances of architectural spaces can be described by a number of parameters (e.g., sound pressure level, sound strength, reverberation time, clarity, etc.), each accounting for di erent perceptual aspects [33,34]. The acoustic requirements vary in accordance with the function hosted in the space. For instance, in spaces intended for speech, as classrooms and conference rooms, early sound reflections need to be adequately controlled to ensure the speech intelligibility [35]. In music venues, i.e., concert halls, opera houses, theatres and open-theatres, a number of parameters are usually considered to account for di erent perceptual aspects [36]. The proper management of early and late reflections is crucial, and it is generally obtained by opportunely treating the ambient with reflective and di usive surfaces. Di erently, the acoustic performance of sound reproduction rooms, like home theatres and recording studios, should be neutral, to prevent the space to alter the perception of recorded sounds; in this case a combination of sound di using and sound absorbing surfaces is preferred [37]. Currently, di erent commercial acoustic simulation tools are available (e.g., Odeon [38], CATT-Acoustic [39], Pachyderm Acoustics [40], etc.), allowing professionals to estimate the performance of design proposals using the geometrical acoustic method. The acoustic performance of a given environment is predicted based on its geometrical features and the acoustic properties of the materials applied to the surfaces. Normally, the acoustic analysis is run in an external application from the modeling environment, and a specific virtual model need to be prepared (e.g., geometrical simplification, surfaces divided into layers based on material and specific format) in order to be fed to the acoustic simulation tool. Besides geometrical acoustic simulations, some more sophisticated simulation methods, such as wave-based ones, have been applied to concert halls and other bigger environments [41–43]. However, these methods still require long simulation time and are not currently supported in any commercial acoustic simulation tool. Although architectural design should pursue aesthetical quality in parallel with acoustic performance objectives, the process of conciliating acoustic requirements and architectural quality is often dicult and time-consuming, given the di erent design approaches and criteria of the two disciplines [44,45]. In most cases, the architectural and acoustic specialists work rather independently, Acoustics 2020, 2 249 with relatively few exchanges between them [28,46]. For instance, the most common approach followed in the design of concert halls relies on well-known typologies (e.g., shoe-box, fan-shaped, vineyard, etc.) and integrates acoustic simulations in late phases of the design process to verify the adherence of the project to performative requirements. In the design of spaces intended for other purposes, acoustic performances are often overlooked, recurring to acoustic treatments to adjust the performances only in late design phases or after the construction. Since the projects at the final stages are already defined, normally, major form-modifications cannot be pursued anymore, and improvements can only be obtained by altering minor design features, resulting often in costly and little e ective solutions [5,6,47,48]. In this frame, the implementation of the PBD method in the acoustic field, known as acoustic performance-based design (APBD), would be able to overcome some of the main drawbacks of the traditional method and set-up an e ective collaboration between architectural and acoustic specialists. The feedback of the simulations enables one to identify the dependencies between the design features and the acoustic performance, and to optimize the project accordingly. However, despite the mentioned advantages, the application of APBD in current architectural practice appears to be limited. 1.3. Objectives The aim of this paper is to provide an overview of the state of the art of the application of the acoustic performance-based design method through the gathering of a set of built case studies. The design procedures followed in the development of the case studies are briefly described, to highlight the benefits of the application of APBD and suggest possible improvements to extend its application. 2. Research Methods This paper presents and investigates a set of 19 built case studies developed with APBD, which were gathered through a literature research. The methodology followed in this work is similar to that applied in review studies pertaining to the architectural field, as in [49]. For this work, unbuilt examples, as well as examples built as scaled prototypes or which lacked adequate documentation, were excluded from the analysis. The research is limited to the publicly available information on the built case studies, which was mainly gathered from journal articles, conference proceedings, books and web articles. Therefore, the presented collection cannot be considered comprehensive, as it excludes the projects, which are not documented in literature, as it is often the case of projects developed by professionals. Moreover, it must be highlighted that, with the exception of case studies developed for research purposes, the publicly released information regarding the design workflow and the performance parameters considered in the optimization process is generally rather limited. Despite these limitations, the presented collection will be hopefully meaningful and will help to delineate the state of the art of the APBD method, by briefly describing the design outcomes, as well as the design processes and the strategies followed to enhance their performances. 2.1. Selection of Case Studies The research was conducted on the literature available on online databases as Scopus [50] and ResearchGate [51], on Google search, and in the academic libraries of Politecnico di Torino. Although scientific literature has been privileged, the support of Google search engine was exploited to extend the collection of case studies and to find further information. It must be noted that, for certain projects, further details were asked to the professionals involved in the projects via personal communications. Common keywords used in the search enquiries to filter results were: “performance-based design”, “form-finding”, “performative design”, “performance”, “architecture”, “design”, “generative”, “optimization”, “simulation”, “acoustics” and “sound”. Only built examples with adequate documentation were selected for the analysis. Acoustics 2020, 2 250 According to these criteria, 19 built examples were collected. In the following section, the case studies were briefly described and information on the design method and the tools used were gathered. 2.2. Case Studies The 19 case studies, which were briefly described in the following sections, were clustered according to their primary purpose and architectural characteristics. The first section, named “music venues” (Section 2.2.1) collected the projects that were designed to support of music and other artistic performances (i.e., concert halls, acoustic shells, etc.), while the second section, named “other spaces” (Section 2.2.2), gathered projects that were meant to host other functions or were developed as artistic installations. 2.2.1. Music Venues The Philharmonie de Paris Design: Ateliers Jean Nouvel, Brigitte Métra Associés; Acoustics: Marshall Day Acoustics, Nagata Acoustics, Studio DAP, Kahle Acoustics, Altia Acoustique, Jean-Paul Lamoureux and ASC; Paris, France, 2015 The project is the winning proposal of an international competition for the Philharmonie de Paris, whose main venue is a 2400 seats concert hall primary used for orchestral acoustic music performances (Figure 1). The acoustic brief for the “Grande Salle” explicitly called for an innovative shape for the concert hall with a limited distance between stage and seats, optimization of both early and late acoustic responses and also defined more than 10 acoustic requirements to be met (sound strength, reverberation time, clarity, etc.). The acoustic design started with the study of the sound reflections through laser measurements in scale models and continued with the support of parametric modeling and acoustic simulation tools, using Grasshopper, Maya [52] and Odeon. The solution adopted is made of two nested chambers that balance early and late reflections: the inner provides acoustical clarity and visual intimacy; the outer provides high reverberation, with an overall volume of 37,700 m . The inner chamber is characterized by the presence of suspended reflectors, called “nuages”, along with the balconies’ fronts and walls, namely “ribbons”, which provide early sound reflections. The design of the “nuages” and “ribbons” was developed though the APBD method, following an iterative form-optimization process guided by the relations between their geometry and the acoustic performance at the audience positions. Initially, the form optimization process was carried out manually, while in subsequent phases it was pursued with the aid of automated processes using Grasshopper and Maya. The “nuages” and “ribbons” have been optimized to provide the desirable amount of early sound reflection over the audience in order to meet the acoustic requirements, such as time delay and level di erence between direct and reflected sound, while also considering architectural and theatrical requirements. Odeon simulations were used after the optimization procedure to further verify the design outcome. Such simulations evidenced that the optimization process lead to significant performance improvements without compromising the architectural concept [53–59]. Acoustics 2020, 2 251 Acoustics 2020, 3 FOR PEER REVIEW 6 Figure 1. Philharmonie de Paris. Image courtesy © William Beaucardet. Figure 1. Philharmonie de Paris. Image courtesy © William Beaucardet. Elbphilharmonie Concert Hall 2.2.1.2. Elbphilharmonie Concert Hall Design: Herzog and de Meuron, Acoustics: Nagata Acoustics; Hamburg, Germany, 2017 The design of the main concert hall of the Elbphilharmonie, the “Grosser Saal” (Figure 2), is based Design: Herzog and de Meuron, Acoustics: Nagata Acoustics; Hamburg, Germany, 2017 on the vineyard configuration and features 2100 seats and a volume of 23,000 m . The APBD approach The design of the main concert hall of the Elbphilharmonie, the “Grosser Saal” (Figure 2), is informed the design of the 10,000 unique acoustic di usive panels that line the ceiling, walls and based on the vineyard configuration and features 2100 seats and a volume of 23,000 m . The APBD balustrades of the venue, whose engraved pattern has been defined through a generative design approach informed the design of the 10,000 unique acoustic diffusive panels that line the ceiling, process. The development of the project involved the use of an acoustic simulation tool, parametric walls and balustrades of the venue, whose engraved pattern has been defined through a generative modeling and optimization systems. Moreover, a 1:10 scale model was also used to test the ecacy design process. The development of the project involved the use of an acoustic simulation tool, of the customized di using panels in eliminating long path echoes. Each group of seating of the parametric modeling and optimization systems. Moreover, a 1:10 scale model was also used to test audience is served by unique gypsum fiberboard panels, to create a balanced reverberation across the efficacy of the customized diffusing panels in eliminating long path echoes. Each group of seating the entire hall. Their design, which is the result of a close collaboration between acousticians and of the audience is served by unique gypsum fiberboard panels, to create a balanced reverberation architectural designers, combines acoustic performance and aesthetics through an irregular pattern of across the entire hall. Their design, which is the result of a close collaboration between acousticians “seashell” cells engraved in their surfaces. The APBD method has been followed in the design of the and architectural designers, combines acoustic performance and aesthetics through an irregular “seashell” pattern, which is optimized to di use sound waves over the seating of the audience and pattern of “seashell” cells engraved in their surfaces. The APBD method has been followed in the to eliminate detrimental echoes. The cells of the pattern feature a width ranging from 40 to 160 mm, design of the “seashell” pattern, which is optimized to diffuse sound waves over the seating of the and a depth ranging from 10 to 90 mm. In particular, in locations where it was required to eliminate audience and to eliminate detrimental echoes. The cells of the pattern feature a width ranging from echoes, the sound scattering performance of the panels were enhanced by the greater depth of the 40 to 160 mm, and a depth ranging from 10 to 90 mm. In particular, in locations where it was required engraved cells, which measures 50–90 mm, while when soft reflections are desired, the cells feature to eliminate echoes, the sound scattering performance of the panels were enhanced by the greater a depth in the range of 10–30 mm. The generation of the pattern of the panels was performed by a depth of the engraved cells, which measures 50–90 mm, while when soft reflections are desired, the custom algorithm, able to define a unique solution for each panel to meet the acoustic requirements. cells feature a depth in the range of 10–30 mm. The generation of the pattern of the panels was In addition to acoustic simulations, also scale model measurements were used to verify the results of performed by a custom algorithm, able to define a unique solution for each panel to meet the acoustic the simulation and ensure the e ectiveness of the pattern in echoes suppression [60–64]. requirements. In addition to acoustic simulations, also scale model measurements were used to verify the results of the simulation and ensure the effectiveness of the pattern in echoes suppression [60– 64]. Acoustics 2020, 2 252 Acoustics 2020, 3 FOR PEER REVIEW 7 Figure 2. The “Grosser Saal” of the Elbphilharmonie. Image courtesy © Maxim Schulz. Figure 2. The “Grosser Saal” of the Elbphilharmonie. Image courtesy © Maxim Schulz. Anneliese Brost Musikforum Ruhr 2.2.1.3. Anneliese Brost Musikforum Ruhr Design: Bez + Kock Architekten; Acoustics: Kahle Acoustics, Müller-BBM; Bochum, Germany, 2016 The project is the winning proposal of the design competition for the concert hall for the Bochum Design: Bez + Kock Architekten; Acoustics: Kahle Acoustics, Müller-BBM; Bochum, Germany, 2016 Symphony Orchestra, which called for a shoe-box venue with a volume of 14,000 m , visual intimacy and The project is the winning proposal of the design competition for the concert hall for the Bochum less than 1000 seats. The concert hall developed by Bez + Kock Architekten conciliates these conflicting Symphony Orchestra, which called for a shoe-box venue with a volume of 14,000 m , visual intimacy goals by locating almost 1/3 of the required volume above the sound-transparent grid-ceiling (Figure 3). and less than 1000 seats. The concert hall developed by Bez + Kock Architekten conciliates these The final solution combines elements of the shoe-box and of the vineyard configurations, as the audience conflicting goals by locating almost 1/3 of the required volume above the sound-transparent grid- surrounds the orchestra. The sense of intimacy is further enhanced by the concave-curved shapes ceiling (Figure 3). The final solution combines elements of the shoe-box and of the vineyard featured by the fronts and undersides of the balconies located at the sides of the venue. The APBD configurations, as the audience surrounds the orchestra. The sense of intimacy is further enhanced method informed the design of these surfaces as well as that of the acoustic canopy suspended above by the concave-curved shapes featured by the fronts and undersides of the balconies located at the the stage. The architectural team collaborated with the acoustic consultants in the design process of sides of the venue. The APBD method informed the design of these surfaces as well as that of the these elements, which was developed using parametric models created in Grasshopper and a custom acoustic canopy suspended above the stage. The architectural team collaborated with the acoustic acoustic simulation tool integrated in the modeling environment. In plan, the curved profiles of the consultants in the design process of these elements, which was developed using parametric models sides and undersides of the balconies were initially determined on the basis of two center-points, created in Grasshopper and a custom acoustic simulation tool integrated in the modeling one in the conductor ’s position and one in the middle of the parterre. In order to prevent the creation environment. In plan, the curved profiles of the sides and undersides of the balconies were initially of sound focuses and echoes resulting from the curvature, these surfaces were segmented, and the determined on the basis of two center-points, one in the conductor’s position and one in the middle curvature and vertical tilting of each portion was optimized based on acoustic simulation feedbacks of the parterre. In order to prevent the creation of sound focuses and echoes resulting from the to provide beneficial sound reflections, enhancing clarity and acoustic envelopment. The acoustic curvature, these surfaces were segmented, and the curvature and vertical tilting of each portion was canopy located above the stage is made of five double-curved and dynamically shaped panels made optimized based on acoustic simulation feedbacks to provide beneficial sound reflections, enhancing of gypsum fiber board. The form of the panels of the canopy was optimized iteratively considering clarity and acoustic envelopment. The acoustic canopy located above the stage is made of five double- acoustic and architectural goals and their final configuration, which features varying curvatures in curved and dynamically shaped panels made of gypsum fiber board. The form of the panels of the cross section, enhances the di usion of the percussion and brass in the venue. Odeon simulations were canopy was optimized iteratively considering acoustic and architectural goals and their final performed in late design phases for verification purposes and found good agreement with the results configuration, which features varying curvatures in cross section, enhances the diffusion of the of the simulations employed to support the design optimization [65–67]. percussion and brass in the venue. Odeon simulations were performed in late design phases for verification purposes and found good agreement with the results of the simulations employed to support the design optimization [65–67]. Acoustics 2020, 2 253 Acoustics 2020, 3 FOR PEER REVIEW 8 Figure 3. Anneliese Brost Musikforum Ruhr. Image courtesy © Mark Wohlrab/architektur-photos.de. Figure 3. Anneliese Brost Musikforum Ruhr. Image courtesy © Mark Wohlrab/architektur-photos.de. Concert Hall of Ureshino Cultural Center 2.2.1.4. Concert Hall of Ureshino Cultural Center Design: AnS Studio, SUEP Architects; Acoustics: Nagata Acoustics; Ureshino, Japan, 2014 Design The : An concert S Studio hall , SUEP (463 Architects seats) is part ; Aof coustic the Cultural s: Nagata Acou Center stics; of the Uresh city of ino, Ur Japan, 2014 eshino and features a shoe-box configuration with a folding roof (Figure 4). In the design of the roof of the concert hall, origami The concert hall (463 seats) is part of the Cultural Center of the city of Ureshino and features a design and acoustic engineering were combined in order to meet the acoustic performance requirements. shoe-box configuration with a folding roof (Figure 4). In the design of the roof of the concert hall, APBD informed the design of the folding roof of the venue, whose final shape is the outcome of an origami design and acoustic engineering were combined in order to meet the acoustic performance interactive design method, which combined a parametric origami software (i.e., a software able to requirements. APBD informed the design of the folding roof of the venue, whose final shape is the generate di erent folding patterns based on origami rules), a custom acoustic simulation program outcome of an interactive design method, which combined a parametric origami software (i.e., a and an optimization tool. The acoustic performance requirements for the venue proposed by the software able to generate different folding patterns based on origami rules), a custom acoustic acoustic consultants were a uniform distribution of sound over the hall and audience within 30–90 ms, simulation program and an optimization tool. The acoustic performance requirements for the venue and the absence of echoes and sound focuses. The design method followed three steps. Initially, all the proposed by the acoustic consultants were a uniform distribution of sound over the hall and audience possible design alternatives for the folding roof were generated by the origami program, according to within 30–90 ms, and the absence of echoes and sound focuses. The design method followed three origami rules and the constraints set by the design team, which were related to building regulations, steps. Initially, all the possible design alternatives for the folding roof were generated by the origami budget, structural aspects and other criteria. Each solution was then analyzed with the custom acoustic program, according to origami rules and the constraints set by the design team, which were related simulation program, with respect to the sound propagation and the distribution of sound at the to building regulations, budget, structural aspects and other criteria. Each solution was then analyzed audience positions. Finally, based on the simulation feedbacks, the optimization tool was used to find with the custom acoustic simulation program, with respect to the sound propagation and the the solution, which showed the best combination of parameters to balance architectural and acoustic distribution of sound at the audience positions. Finally, based on the simulation feedbacks, the goals. The final solution for the roof, which was selected by the optimization program among a pool of optimization tool was used to find the solution, which showed the best combination of parameters to about 200 design alternatives, is based on the Miura-ori folding pattern [68], where the folding depths balance architectural and acoustic goals. The final solution for the roof, which was selected by the and angles have been selected based on acoustic simulation feedback [28,69]. optimization program among a pool of about 200 design alternatives, is based on the Miura-ori folding pattern [68], where the folding depths and angles have been selected based on acoustic simulation feedback [28,69]. Acoustics 2020, 2 254 Acoustics 2020, 3 FOR PEER REVIEW 9 Figure 4. Concert Hall of Ureshino Cultural Center. Image courtesy © Kai Nakamura. Figure 4. Concert Hall of Ureshino Cultural Center. Image courtesy © Kai Nakamura. University of Iowa Concert Hall 2.2.1.5. University of Iowa Concert Hall Design: LMN Architects, Neumann Monson Architects. Acoustics: Ja e Holden; Iowa City, IA, USA, 2016 Design: LMN Architects, Neumann Monson Architects. Acoustics: Jaffe Holden; Iowa City, IA, USA, The 700 seats-concert hall represents the main venue of the Voxman Music Building of the University of Iowa. The concert hall is based on the shoe-box configuration and features a sculpted The 700 seats-concert hall represents the main venue of the Voxman Music Building of the structure suspended from the ceiling, made of 946 unique folded aluminum composite modules, which University of Iowa. The concert hall is based on the shoe-box configuration and features a sculpted was generated through performance-based design (Figure 5). The structure integrates and rationalizes structure suspended from the ceiling, made of 946 unique folded aluminum composite modules, in a unique and aesthetically unified solution five technical systems: acoustics, stage lighting, house which was generated through performance-based design (Figure 5). The structure integrates and lighting, audio-visual and fire protection. The form-finding process, which guided the design of the rationalizes in a unique and aesthetically unified solution five technical systems: acoustics, stage structure was enabled by a collaborative parametric model developed in Grasshopper, which was lighting, house lighting, audio-visual and fire protection. The form-finding process, which guided optimized in light of the objectives defined by the consultants of the di erent disciplines involved. the design of the structure was enabled by a collaborative parametric model developed in The project was guided by an iterative design method and was also optimized for fabrication and to be Grasshopper, which was optimized in light of the objectives defined by the consultants of the delivered in a low-bid procurement environment. As regards acoustics, the feedbacks from a custom different disciplines involved. The project was guided by an iterative design method and was also ray-tracing simulation tool, developed in collaboration with the acousticians, were used to drive the optimized for fabrication and to be delivered in a low-bid procurement environment. As regards design optimization process of the ceiling system. This enabled the architects to autonomously run acoustics, the feedbacks from a custom ray-tracing simulation tool, developed in collaboration with preliminary acoustic analyses to test the design iterations in early design phases. In particular, the form the acousticians, were used to drive the design optimization process of the ceiling system. This of the ceiling system was progressively refined to ensure an even distribution of the reflected sound enabled the architects to autonomously run preliminary acoustic analyses to test the design iterations waves towards the audience and toward the upper portion of the side walls. Given the number of in early design phases. In particular, the form of the ceiling system was progressively refined to disciplines involved, SketchUp [70] and Revit [71] versions of the parametric model had to be used ensure an even distribution of the reflected sound waves towards the audience and toward the upper to allow exchanges among the di erent consultants. Early prototypes of panels and connections of portion of the side walls. Given the number of disciplines involved, SketchUp [70] and Revit [71] the ceiling system were produced at di erent scales and tested. Iterations between physical and versions of the parametric model had to be used to allow exchanges among the different consultants. digital models were used to further refine the project and explore di erent fabrication strategies. Great Early prototypes of panels and connections of the ceiling system were produced at different scales commitment was placed in optimizing the fabrication of the system, and direct-to-fabrication data for and tested. Iterations between physical and digital models were used to further refine the project and construction could be generated from the model [72–74]. explore different fabrication strategies. Great commitment was placed in optimizing the fabrication of the system, and direct-to-fabrication data for construction could be generated from the model [72– 74]. Acoustics 2020, 2 255 Acoustics 2020, 3 FOR PEER REVIEW 10 Figure 5. University of Iowa Concert Hall. Image courtesy © Tim Grith. Figure 5. University of Iowa Concert Hall. Image courtesy © Tim Griffith. Symphony Hall of the Fuzhou Strait Culture and Art Centre 2.2.1.6. Symphony Hall of the Fuzhou Strait Culture and Art Centre Design: PES-Architects, Acoustics: Tongji Architectural Design Group, Kahle Acoustics and Akukon; Design: PE Mawei S-Archit New ects T, own, Acoust Fuzhou, ics: Ton China, gji Arch 2018 itectural Design Group, Kahle Acoustics and Akukon; Mawei The New Town, Fuzhou Strait Fuzh Cultur ou, Chi e and na, 2Art 018 Centre includes a 1000 seat symphony hall and a 1600 seat opera hall, both of which were developed with the APBD approach. The Fuzhou Strait Culture and Art Centre includes a 1000 seat symphony hall and a 1600 seat The symphony hall of the Strait Culture and Art Centre in Fuzhou features a vineyard configuration opera hall, both of which were developed with the APBD approach. and, despite the relatively modest seat capacity, is meant to host a full symphony orchestra of more The symphony hall of the Strait Culture and Art Centre in Fuzhou features a vineyard than 100 musicians (Figure 6). In order to prevent overly loud acoustics, its volume was set at 17,000 m configuration and, despite the relatively modest seat capacity, is meant to host a full symphony and was visually divided in two parts by the suspended reflectors, which overlook the audience. orchestra of more than 100 musicians (Figure 6). In order to prevent overly loud acoustics, its volume The curvature of the suspended reflectors ensures an even coverage of early reflections, but the major was set at 17,000 m and was visually divided in two parts by the suspended reflectors, which role is played by the walls of the halls, which are shaped as convex sphere portions. The walls that overlook the audience. The curvature of the suspended reflectors ensures an even coverage of early separate the terraces of the audience and those at the periphery of the hall are inclined in a petal-like reflections, but the major role is played by the walls of the halls, which are shaped as convex sphere configuration. The lower portions of these elements generate early reflections, while the upper parts portions. The walls that separate the terraces of the audience and those at the periphery of the hall spread the sound energy in the venue. The surface of the petals is coated with ceramic tiles with are inclined in a petal-like configuration. The lower portions of these elements generate early di erent textures and patterns, to provide either specular or di use reflections. The APBD approach reflections, while the upper parts spread the sound energy in the venue. The surface of the petals is informed the design of the geometrical features and surface patterns of these petals. Grasshopper was coated with ceramic tiles with different textures and patterns, to provide either specular or diffuse used to generate the parametric models, while a custom tool integrated in the modeling environment reflections. The APBD approach informed the design of the geometrical features and surface patterns was used to analyze the acoustic performance according to the early acoustic eciency approach [75]. of these petals. Grasshopper was used to generate the parametric models, while a custom tool integrated in the modeling environment was used to analyze the acoustic performance according to the early acoustic efficiency approach [75]. As regard the geometrical features, the distribution and Acoustics 2020, 2 256 Acoustics 2020, 3 FOR PEER REVIEW 11 As regard the geometrical features, the distribution and vertical tilting angles of the “petals” were vertical tilting angles of the “petals” were optimized to provide early lateral reflections to all the optimized to provide early lateral reflections to all the audience blocks. The surface pattern of specularly audience blocks. The surface pattern of specularly reflecting or diffusing ceramic tiles was used reflecting or di using ceramic tiles was used generate useful early reflections and to prevent undesired generate useful early reflections and to prevent undesired echoes from the upper portions of the echoes from the upper portions of the petals. Since it was considered crucial to maintain strong early petals. Since it was considered crucial to maintain strong early reflections, the sound diffusing tile reflections, the sound di using tile pattern was applied only in the portion of the petals creating pattern was applied only in the portion of the petals creating potentially harmful late reflections, potentially harmful late reflections, while the remaining part was left with a specularly reflective finish. while the remaining part was left with a specularly reflective finish. Such surfaces were identified by Such surfaces were identified by using a custom algorithm able to categorize the surface facets based using a custom algorithm able to categorize the surface facets based on the delay of the reflections on the delay of the reflections they may generate, considering the combined data from four sound they may generate, considering the combined data from four sound source positions. Although the source positions. Although the surfaces were identified by the algorithm, when conflicting feedbacks surfaces were identified by the algorithm, when conflicting feedbacks were found, the final decision were found, the final decision was left to the operator. Odeon simulations were used in late design was left to the operator. Odeon simulations were used in late design phases for verification purposes phases for verification purposes [76]. [76]. Figure 6. Symphony Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy© Marc Goodwin. Figure 6. Symphony Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Opera Hall of the Fuzhou Strait Culture and Art Centre 2.2.1.7. Opera Hall of the Fuzhou Strait Culture and Art Centre Design: PES-Architects, Acoustics: Tongji Architectural Design Group, Kahle Acoustics and Akukon; Mawei New Town, Fuzhou, China, 2018 Design: PES-Architects, Acoustics: Tongji Arch3 itectural Design Group, Kahle Acoustics and Akukon; The 1600-seat opera hall (volume 14,500 m ) is based on the horseshoe configuration and features Mawei New Town, Fuzhou, China, 2018 a continuous skin, with convex and concave curvatures, which defines and unifies walls, balconies and ceiling (Figure 7). The APBD approach was applied to define the form of the skin, which was optimized The 1600-seat opera hall (volume 14,500 m ) is based on the horseshoe configuration and features in order to meet the acoustic requirements of creating a homogenous coverage of strong early lateral a continuous skin, with convex and concave curvatures, which defines and unifies walls, balconies reflections over the entire audience and to avoid undesired focusing e ects. The acoustic simulations and ceiling (Figure 7). The APBD approach was applied to define the form of the skin, which was were performed with a custom tool based on a di erential ray-tracing technique [77], integrated in the optimized in order to meet the acoustic requirements of creating a homogenous coverage of strong modeling environment. Since the architectural elements are not present as individual entities but are early lateral reflections over the entire audience and to avoid undesired focusing effects. The acoustic interlinked by the skin, they could not be singularly adjusted, as any form change would impact on simulations were performed with a custom tool based on a differential ray-tracing technique [77], the other elements. Therefore, the continuous envelope was modeled parametrically in Grasshopper, integrated in the modeling environment. Since the architectural elements are not present as and directly optimized based on the acoustic feedbacks, due to the close collaboration between the individual entities but are interlinked by the skin, they could not be singularly adjusted, as any form architectural and acoustic teams. In particular, the skin was subdivided in smaller patches, and each change would impact on the other elements. Therefore, the continuous envelope was modeled was assigned with an acoustic target, such as creating early reflections or enhancing late reverberation. parametrically in Grasshopper, and directly optimized based on the acoustic feedbacks, due to the The orientation of the di erent skin portions was then iteratively optimized by the operators in order close collaboration between the architectural and acoustic teams. In particular, the skin was to achieve their target performance requirements and then combined to create the final smooth curved subdivided in smaller patches, and each was assigned with an acoustic target, such as creating early skin. A fine-scale texture of flower-shaped ceramic tiles is applied to the surfaces of the continuous skin; reflections or enhancing late reverberation. The orientation of the different skin portions was then the small irregularities of the pattern provide sound scattering at high frequencies. The final outcome iteratively optimized by the operators in order to achieve their target performance requirements and then combined to create the final smooth curved skin. A fine-scale texture of flower-shaped ceramic tiles is applied to the surfaces of the continuous skin; the small irregularities of the pattern provide Acoustics 2020, 2 257 Acoustics 2020, 3 FOR PEER REVIEW 12 of the optimization was further tested in Odeon; the verification confirmed the benefits provided by sound scattering at high frequencies. The final outcome of the optimization was further tested in the application of APBD [76,78]. Odeon; the verification confirmed the benefits provided by the application of APBD [76,78]. Figure 7. Opera Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Figure 7. Opera Hall of the Fuzhou Strait Culture and Art Centre. Image courtesy © Marc Goodwin. Conga Room 2.2.1.8. Conga Room Design: Belzberg Architects, Acoustics: Newson Brown Acoustics; Los Angeles, CA, USA, 2008 Design: Belzberg Architects, Acoustics: Newson Brown Acoustics; Los Angeles, CA, USA, 2008 The Conga Room dance club hosts a series of a multitude of programs (dance hall, stage, restaurant, bars and VIP areas) and is located at the second floor of a multipurpose building, mainly The Conga Room dance club hosts a series of a multitude of programs (dance hall, stage, occupied by oces. Due to a retrofit intervention, the existing spaces were acoustically insulated restaurant, bars and VIP areas) and is located at the second floor of a multipurpose building, mainly and adapted to host the new mixed functions. The bold design of the undulating ceiling system is occupied by offices. Due to a retrofit intervention, the existing spaces were acoustically insulated and meant to visually attract clients while also providing acoustic treatment for the dance hall (Figure 8). adapted to host the new mixed functions. The bold design of the undulating ceiling system is meant The ceiling was indeed identified as the most e ective location for acoustic treatments to provide to visually attract clients while also providing acoustic treatment for the dance hall (Figure 8). The sound insulation and amplification. The ceiling system was developed through performance-based ceiling was indeed identified as the most effective location for acoustic treatments to provide sound design, exploiting the functions o ered by CATIA [79] and Rhinoceros for modeling, and Ecotect [80] insulation and amplification. The ceiling system was developed through performance-based design, for the simulations. The ceiling system, made of CNC-milled plywood panels whose pattern and exploiting the functions offered by CATIA [79] and Rhinoceros for modeling, and Ecotect [80] for the fashion changes di erentiate the various environments of the club, was designed to address acoustic simulations. The ceiling system, made of CNC-milled plywood panels whose pattern and fashion issues and to integrate several building infrastructures (house lighting, mechanical, audio-visual, fire changes differentiate the various environments of the club, was designed to address acoustic issues protection, etc.). The model of the ceiling structure was iteratively optimized based on the feedback and to integrate several building infrastructures (house lighting, mechanical, audio-visual, fire from the various specialists involved and performance simulation. In particular, the ceiling panels protection, etc.). The model of the ceiling structure was iteratively optimized based on the feedback over the dance hall are morphed into flower-like structures, which control the acoustic performance of from the various specialists involved and performance simulation. In particular, the ceiling panels the ceiling. The di erent arrangements and tilting of the flowers’ petals have been optimized based on over the dance hall are morphed into flower-like structures, which control the acoustic performance acoustic simulation feedback to provide the desired amount of sound absorption [81–84]. of the ceiling. The different arrangements and tilting of the flowers’ petals have been optimized based on acoustic simulation feedback to provide the desired amount of sound absorption [81–84]. Acoustics 2020, 2 258 Acoustics 2020, 3 FOR PEER REVIEW 13 Figure 8. Conga Room. Image courtesy © Benny Chan/Fotoworks. Figure 8. Conga Room. Image courtesy © Benny Chan/Fotoworks. Stage by the Sea 2.2.1.9. Stage by the Sea Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; Littlehampton, UK, 2014 The project consists of two double-curved concrete shells located close to the coastline of Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; Littlehampton, UK, 2014 Littlehampton, United Kingdom. The smaller shell works as a shelter, while the bigger one is an The project consists of two double-curved concrete shells located close to the coastline of acoustic shell that is used as a stage for outdoor concerts and projects the sounds towards the listeners Littlehampton, United Kingdom. The smaller shell works as a shelter, while the bigger one is an (Figure 9). During the design process of the acoustic shell, great commitment was placed in combining acoustic shell that is used as a stage for outdoor concerts and projects the sounds towards the listeners structural, acoustics and aesthetic goals in a unique solution. The final design of the acoustic shell is the (Figure 9). During the design process of the acoustic shell, great commitment was placed in result of an ABPD process, and conjugates the key acoustic performance requirements with architectural combining structural, acoustics and aesthetic goals in a unique solution. The final design of the and structural objectives to create a durable, e ective and inexpensive solution. The design process acoustic shell is the result of an ABPD process, and conjugates the key acoustic performance involved the use of Grasshopper for Rhinoceros for modeling, Dynamo for Revit [71,85] for the acoustic requirements with architectural and structural objectives to create a durable, effective and simulations and Galapagos for the design optimization. The design of the structure was developed in inexpensive solution. The design process involved the use of Grasshopper for Rhinoceros for a tight collaboration between architects and technical consultants, which enabled us to find the best modeling, Dynamo for Revit [71,85] for the acoustic simulations and Galapagos for the design compromise in overall terms. The digital model of the shell was exchanged among the professionals optimization. The design of the structure was developed in a tight collaboration between architects involved more than twenty times before its final configuration was achieved. The acoustic analysis and technical consultants, which enabled us to find the best compromise in overall terms. The digital enabled one to define a shape for the acoustic shell able to e ectively support outdoor concerts by model of the shell was exchanged among the professionals involved more than twenty times before reflecting the sounds towards the audience located in the facing sunken garden, allowing the music to its final configuration was achieved. The acoustic analysis enabled one to define a shape for the be perfectly heard in windy conditions at a distance of 50 m from the stage [86–90]. acoustic shell able to effectively support outdoor concerts by reflecting the sounds towards the audience located in the facing sunken garden, allowing the music to be perfectly heard in windy conditions at a distance of 50 m from the stage [86–90]. Acoustics 2020, 2 259 Acoustics 2020, 3 FOR PEER REVIEW 14 Figure Figure 9. 9. Stage Stage by the Sea by the Sea.. Im Image age cour courtesy tesy © © Flanagan Lawrence. Flanagan Lawrence. Resonant String Shell (ReS) 6.0 2.2.1.10. Resonant String Shell (ReS) 6.0 Design: Sergio Pone, Bianca Parenti, Daniele Lancia, Sofia Colabella; Acoustics: Serafino Di Design: Sergio Pone, Bianca Parenti, Daniele Lancia, Sofia Colabella; Acoustics: Serafino Di Rosario; Rosario; Acireale, Italy, 2017 Acireale, Italy, 2017 ReS is a temporary outdoor acoustic shell that hosts the classical music concerts of the yearly festival “Villa Pennisi in Musica”. The shell design combines acoustic concerns with structural and ReS is a temporary outdoor acoustic shell that hosts the classical music concerts of the yearly technological ones. During each edition of the festival, a prototype of a temporary outdoor acoustic festival “Villa Pennisi in Musica”. The shell design combines acoustic concerns with structural and shell is built in the framework of a summer school, and its performances are tested though acoustic technological ones. During each edition of the festival, a prototype of a temporary outdoor acoustic measurements. From year to year, the design of the shell is optimized based on the measured acoustic shell is built in the framework of a summer school, and its performances are tested though acoustic performance and a new design is developed to be built in the following edition. The acoustic shell built measurements. From year to year, the design of the shell is optimized based on the measured acoustic in 2017, named ReS 6.0 (Figure 10), was developed exploiting a multiobjective optimization process performance and a new design is developed to be built in the following edition. The acoustic shell to define the geometry of the shell. In particular, the inner profile of the shell, which is composed built in 2017, named ReS 6.0 (Figure 10), was developed exploiting a multiobjective optimization by wooden reflective panels, anchored to an already defined structural system made of arches, was process to define the geometry of the shell. In particular, the inner profile of the shell, which is optimized within a magnitude of 50 cm. The process was enabled by Octopus [25], a multiobjective composed by wooden reflective panels, anchored to an already defined structural system made of optimization tool, Grasshopper and a custom acoustic simulation tool based on an image-source arches, was optimized within a magnitude of 50 cm. The process was enabled by Octopus [25], a method. Considering three pairs of sound sources located within the shell (i.e., music performers), multiobjective optimization tool, Grasshopper and a custom acoustic simulation tool based on an the profile of the shell was optimized to maximize the evenness of sound energy in the audience image-source method. Considering three pairs of sound sources located within the shell (i.e., music positions. The sound energy was described by the sound pressure level and the standard deviation was performers), the profile of the shell was optimized to maximize the evenness of sound energy in the calculated to quantify its rate of homogeneity. For each couple of sound sources, the sound pressure audience positions. The sound energy was described by the sound pressure level and the standard level has been estimated using the custom acoustic simulation tool, and Galapagos was used to search deviation was calculated to quantify its rate of homogeneity. For each couple of sound sources, the for solutions able to minimize the standard deviation. The optimization process identified a set of sound pressure level has been estimated using the custom acoustic simulation tool, and Galapagos “equally optimal” solutions, among which the final configuration was selected by considering also was used to search for solutions able to minimize the standard deviation. The optimization process aesthetic criteria. CATT-Acoustic was used in late design phases to run more accurate analyses of the identified a set of “equally optimal” solutions, among which the final configuration was selected by optimized shell. The field measurement confirmed that the form optimization leads to a greater and considering also aesthetic criteria. CATT-Acoustic was used in late design phases to run more more uniform distribution of sound energy in the audience [46]. accurate analyses of the optimized shell. The field measurement confirmed that the form optimization leads to a greater and more uniform distribution of sound energy in the audience [46]. Acoustics 2020, 2 260 Acoustics 2020, 3 FOR PEER REVIEW 15 Figure 10. ReS 6.0. Image courtesy © Daniele Lancia. Figure 10. ReS 6.0. Image courtesy © Daniele Lancia. Soundforms 2.2.1.11. Soundforms Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; London, UK, 2012 Soundforms is a movable acoustic shell designed to support outdoor classic music performances, Design: Flanagan Lawrence Architects; Acoustics: Arup Acoustics; London, UK, 2012 by improving the ability of musicians of the ensemble to hear each other, and by projecting the sound Soundforms is a movable acoustic shell designed to support outdoor classic music generated towards the audience. A prototype of the shell, developed for small chamber music orchestra, performances, by improving the ability of musicians of the ensemble to hear each other, and by was built and tested in London’s Dockland, and was then selected to be installed in the Olympic Park projecting the sound generated towards the audience. A prototype of the shell, developed for small for the 2012 London Olympic Games to host music concerts during the event (Figure 11). The acoustic chamber music orchestra, was built and tested in London’s Dockland, and was then selected to be performances were one of the major drivers of the design process, aside with the development of installed in the Olympic Park for the 2012 London Olympic Games to host music concerts during the the structure and its optimization for transport and assembly. The shell form was developed from a event (Figure 11). The acoustic performances were one of the major drivers of the design process, portion of torus, and features an upper peak, which was designed to project as much sound as possible aside with the development of the structure and its optimization for transport and assembly. The towards the listeners, playing a role similar to that of the ceilings of concert halls. The shell has an shell form was developed from a portion of torus, and features an upper peak, which was designed inflatable skin made of eight PVC coated polyester cushions, fixed to the truss structure. The side walls to project as much sound as possible towards the listeners, playing a role similar to that of the ceilings of the acoustic shell, which performs as reflectors, are integrated in the inner structure of the shell and of concert halls. The shell has an inflatable skin made of eight PVC coated polyester cushions, fixed are visually covered by an acoustically transparent fabric liner, thus enabling one to maintain the visual to the truss structure. The side walls of the acoustic shell, which performs as reflectors, are integrated aspects of the shell without compromising their acoustic performances. Removable reflective panels are in the inner structure of the shell and are visually covered by an acoustically transparent fabric liner, installed within the shell, with the objective to balance the amount of sound energy di used towards thus enabling one to maintain the visual aspects of the shell without compromising their acoustic the orchestra and projected towards the audience. The APBD method informed the development of performances. Removable reflective panels are installed within the shell, with the objective to balance the convex profiles of the reflectors, as well as their deployment within the shell, which, in the built the amount of sound energy diffused towards the orchestra and projected towards the audience. The prototype, were optimized for a small chamber orchestra. The optimized reflectors were developed by APBD method informed the development of the convex profiles of the reflectors, as well as their the acoustic consultants in close collaboration with the design team, following a process of subsequent deployment within the shell, which, in the built prototype, were optimized for a small chamber optimization combining architectural and acoustic objectives with fabrication and constructability orchestra. The optimized reflectors were developed by the acoustic consultants in close collaboration criteria. The reflectors facets were parameterized in Grasshopper, the acoustic simulations were run with the design team, following a process of subsequent optimization combining architectural and using a custom ray-tracing script in Dynamo for Revit, while the optimization process was performed acoustic objectives with fabrication and constructability criteria. The reflectors facets were with the support of automated routines using Galapagos. The final solution was then further tested in parameterized in Grasshopper, the acoustic simulations were run using a custom ray-tracing script Odeon to validate the results [27,91–93]. in Dynamo for Revit, while the optimization process was performed with the support of automated routines using Galapagos. The final solution was then further tested in Odeon to validate the results [27,91–93]. Acoustics 2020, 2 261 Acoustics 2020, 3 FOR PEER REVIEW 16 Figure 11. Soundforms. Image courtesy © Nick Guttridge. Figure 11. Soundforms. Image courtesy © Nick Guttridge. Tiara Acoustic Shell 2.2.1.12. Tiara Acoustic Shell Design and acoustics: Alban Bausset, Willem Boning, Arup Acoustics; Fishtail, MT, USA, 2014–2015 The design of the acoustical shell for the Tippet Rise Art Center was commissioned to Arup Design and acoustics: Alban Bausset, Willem Boning, Arup Acoustics; Fishtail, MT, USA, 2014–2015 Acoustics in 2014. The demountable and transportable shell was initially designed to host and support The design of the acoustical shell for the Tippet Rise Art Center was commissioned to Arup outdoor chamber music concerts for an audience of 50–60 people, by creating an intimate performance Acoustics in 2014. The demountable and transportable shell was initially designed to host and space, visually open to the surroundings natural environment (Figure 12). The shell is made of wooden support outdoor chamber music concerts for an audience of 50–60 people, by creating an intimate panels, which represent the upper corners of the side and front corners of a fan-shaped room, while the performance space, visually open to the surroundings natural environment (Figure 12). The shell is rest of the enclosing surfaces were removed to open the view towards the natural setting. made of wooden panels, which represent the upper corners of the side and front corners of a fan- The goal was to generate a unified acoustic environment for both audience and performers and shaped room, while the rest of the enclosing surfaces were removed to open the view towards the an enveloping sound impression, despite the lack of reverberation. The virtual model of the shell was natural setting. parameterized using Grasshopper. The acoustic performances of the structure were investigated using The goal was to generate a unified acoustic environment for both audience and performers and a custom simulation tool based on an image-source method; a source position and 50 receiver positions an enveloping sound impression, despite the lack of reverberation. The virtual model of the shell was were used. Based on the performance feedbacks, Galapagos was used to optimize the parametric parameterized using Grasshopper. The acoustic performances of the structure were investigated model by adjusting six parameters controlling the shell form, in order to ensure a broad spread of using a custom simulation tool based on an image-source method; a source position and 50 receiver early energy over the entire audience. The variation space of the model parameters was set based on positions were used. Based on the performance feedbacks, Galapagos was used to optimize the structural requirements, and in order to prevent the shell from obscuring the view of the mountain parametric model by adjusting six parameters controlling the shell form, in order to ensure a broad in the background. The fitness function counted the second and third order of reflections over the spread of early energy over the entire audience. The variation space of the model parameters was set “poorest” receivers of the audience. From the two solution regions found by Galapagos, the design based on structural requirements, and in order to prevent the shell from obscuring the view of the team selected the final one based on structural criteria. In 2015, the initial design solution was further mountain in the background. The fitness function counted the second and third order of reflections expanded in order to accommodate up to 80 people, by the addition of two kinks to the structure, which over the “poorest” receivers of the audience. From the two solution regions found by Galapagos, the were optimized with a procedure similar to that used for the initial solution. The final configuration of design team selected the final one based on structural criteria. In 2015, the initial design solution was the shell provides on average 5.6 s- and third-order reflections to each receiver, with a minimum of one further expanded in order to accommodate up to 80 people, by the addition of two kinks to the from the front, one from the right side and one from the left side [94]. structure, which were optimized with a procedure similar to that used for the initial solution. The final configuration of the shell provides on average 5.6 s- and third-order reflections to each receiver, with a minimum of one from the front, one from the right side and one from the left side [94]. Acoustics 2020, 2 262 Acoustics 2020, 3 FOR PEER REVIEW 17 Figure 12. Tippet Rise Art Center, MT. Photo: Erik Petersen © 2017 Tippet Rise. Figure 12. Tippet Rise Art Center, MT. Photo: Erik Petersen © 2017 Tippet Rise. Aalborg Acoustic Pavilion 2011 2.2.1.13. Aalborg Acoustic Pavilion 2011 Design and acoustics: AREA, Electrotexture Lab; Aalborg, Denmark, 2011 The temporary acoustic pavilion was developed within a research framework. The structure is Design and acoustics: AREA, Electrotexture Lab; Aalborg, Denmark, 2011 meant to host electronic music performance and its design was optimized for both acoustic performances The temporary acoustic pavilion was developed within a research framework. The structure is and constructive feasibility. The structure is composed by CNC milled plywood plates, which works meant to host electronic music performance and its design was optimized for both acoustic as sound reflectors (Figure 13). The design process was enabled by the combined use of Grasshopper, performances and constructive feasibility. The structure is composed by CNC milled plywood plates, a custom acoustic simulation tool and Galapagos solver, which allowed one to combine acoustic goals which works as sound reflectors (Figure 13). The design process was enabled by the combined use of with production and assembly criteria. The pavilion was also optimized with the aim to open its Grasshopper, a custom acoustic simulation tool and Galapagos solver, which allowed one to combine geometry towards the water while closing it towards the close-by road, to shield it from trac noise. acoustic goals with production and assembly criteria. The pavilion was also optimized with the aim During the design process, the design problem has been progressively reformulated, in order to reduce to open its geometry towards the water while closing it towards the close-by road, to shield it from the variation space evaluated by the Galapagos solver. With respect to acoustics, the volume of the traffic noise. During the design process, the design problem has been progressively reformulated, in pavilion and the configuration of the reflectors, which define the envelope of the shell, were optimized order to reduce the variation space evaluated by the Galapagos solver. With respect to acoustics, the in two subsequent steps. In order to prevent the structure from altering the electronic music spread volume of the pavilion and the configuration of the reflectors, which define the envelope of the shell, via a loudspeaker, the optimization processes aimed to minimize the reverberation time within the were optimized in two subsequent steps. In order to prevent the structure from altering the electronic pavilion, calculated with the Sabine equation. This goal was reached by maximizing the number music spread via a loudspeaker, the optimization processes aimed to minimize the reverberation time of reflections occurring among reflectors, thus enhancing sound absorption, and by directing the within the pavilion, calculated with the Sabine equation. This goal was reached by maximizing the reflected sound away from the pavilion. The optimization was performed considering di erent sound number of reflections occurring among reflectors, thus enhancing sound absorption, and by directing source positions, which marked the loudspeaker locations in the corners of the pavilion. In particular, the reflected sound away from the pavilion. The optimization was performed considering different the arrangement of the specific set of reflectors serving each loudspeaker was optimized to maximize sound source positions, which marked the loudspeaker locations in the corners of the pavilion. In sound absorption by increasing the number of reciprocal reflections. In the end, the final solution was particular, the arrangement of the specific set of reflectors serving each loudspeaker was optimized slightly refined to meet the fabrication requirements [95,96]. to maximize sound absorption by increasing the number of reciprocal reflections. In the end, the final solution was slightly refined to meet the fabrication requirements [95,96]. Acoustics 2020, 2 263 Acoustics 2020, 3 FOR PEER REVIEW 18 Figure 13. Aalborg Acoustic Pavilion 2011. Image courtesy © Isak Worre Foged. Figure 13. Aalborg Acoustic Pavilion 2011. Image courtesy © Isak Worre Foged. Aalborg Acoustic Pavilion 2012 2.2.1.14. Aalborg Acoustic Pavilion 2012 Design and acoustics: AREA, Mads Brath Jensen; Aalborg, Denmark, 2012 The pavilion is composed of an origami folded structure made of triangular wooden panels Design and acoustics: AREA, Mads Brath Jensen; Aalborg, Denmark, 2012 (Figure 14). The temporary pavilion was developed for research purposes and is intended to host The pavilion is composed of an origami folded structure made of triangular wooden panels two subspaces with di erent purposes, which are therefore characterized by dissimilar acoustic (Figure 14). The temporary pavilion was developed for research purposes and is intended to host two performances. A design optimization process was set in the in order to create two areas with opposite subspaces with different purposes, which are therefore characterized by dissimilar acoustic acoustic proprieties within the pavilion: a zone intended for classical music performances, featuring a performances. A design optimization process was set in the in order to create two areas with opposite long reverberation time, and an area intended for speech, with a short reverberation time. The tools acoustic proprieties within the pavilion: a zone intended for classical music performances, featuring used in the development of the acoustic pavilion are Grasshopper, a custom acoustic simulation a long reverberation time, and an area intended for speech, with a short reverberation time. The tools tool and Galapagos solver. The acoustic performances on the listener positions were described by used in the development of the acoustic pavilion are Grasshopper, a custom acoustic simulation tool the reverberation time, calculated with the Millington-Sette equation, and by sound pressure level, and Galapagos solver. The acoustic performances on the listener positions were described by the simulated using a custom ray-tracing tool. The parametric model of the pavilion was composed reverberation time, calculated with the Millington-Sette equation, and by sound pressure level, by two subsystems: the first controls the overall space form, which resemble a tunnel; the second simulated using a custom ray-tracing tool. The parametric model of the pavilion was composed by defines the folding structure and presents a higher control point resolution. The panels of the pavilion two subsystems: the first controls the overall space form, which resemble a tunnel; the second defines feature a sandwich structure with foam in the middle layer and plywood on both sides. Three panel the folding structure and presents a higher control point resolution. The panels of the pavilion feature variants were developed in order to provide three di erent rates of sound absorption, by opportunely a sandwich structure with foam in the middle layer and plywood on both sides. Three panel variants perforating the interior plywood side of the panel, and therefore exposing the sound absorptive foam were developed in order to provide three different rates of sound absorption, by opportunely layer to the impinging sound waves. The optimization process was able to control the orientations perforating the interior plywood side of the panel, and therefore exposing the sound absorptive foam of the control point of the primary and secondary subsystems, as well as the acoustic variants of the layer to the impinging sound waves. The optimization process was able to control the orientations of wooden panels, which compose of the structure. After 700 iterations, the reverberation times in the the control point of the primary and secondary subsystems, as well as the acoustic variants of the two subzones of the design solutions generated by the optimization process stabilize at values of 0.2 s wooden panels, which compose of the structure. After 700 iterations, the reverberation times in the and 1.4 s [97]. two subzones of the design solutions generated by the optimization process stabilize at values of 0.2 s and 1.4 s [97]. Acoustics 2020, 2 264 Acoustics 2020, 3 FOR PEER REVIEW 19 Figure 14. Aalborg Acoustic Pavilion 2012. Image courtesy © Isak Worre Foged. Figure 14. Aalborg Acoustic Pavilion 2012. Image courtesy © Isak Worre Foged. Resonant Chamber 2.2.1.15. Resonant Chamber Design: RVTR; Acoustics: Arup Acoustics; Ann Arbor, MI, USA, 2012 Resonant Chamber is a responsive acoustic envelope system, based on rigid origami principles, Design: RVTR; Acoustics: Arup Acoustics; Ann Arbor, MI, USA, 2012 that is able to dynamically alter the sound environment in which it is installed based on a set of inputs Resonant Chamber is a responsive acoustic envelope system, based on rigid origami principles, collected in real time by sensors or using preprogrammed configurations (Figure 15). The flexible that is able to dynamically alter the sound environment in which it is installed based on a set of inputs structure can be deployed in a music venue to alter the sound during the performance, playing the role collected in real time by sensors or using preprogrammed configurations (Figure 15). The flexible of an instrument at the architectural scale itself, or can be installed in more ordinary spaces, to calibrate structure can be deployed in a music venue to alter the sound during the performance, playing the their acoustic performances to given requirements. The faceted “sound cloud” is able to dynamically role of an instrument at the architectural scale itself, or can be installed in more ordinary spaces, to transform its configuration in response to acoustic changing conditions and to variations in the listeners’ calibrate their acoustic performances to given requirements. The faceted “sound cloud” is able to positions. The tools used to develop the project were Grasshopper, a ray-tracing tool for acoustic dynamically transform its configuration in response to acoustic changing conditions and to variations simulations and Kangaroo [98], to model the dynamic deformation of the system. The structure is in the listeners’ positions. The tools used to develop the project were Grasshopper, a ray-tracing tool made of a combination of di erent plywood panels, featuring either sound reflective, sound absorbing for acoustic simulations and Kangaroo [98], to model the dynamic deformation of the system. The or electroacoustic properties, arranged around an electronic panel that contains circuit controls and structure is made of a combination of different plywood panels, featuring either sound reflective, sensing inputs. In response to the inputs, such as ideal reverberation time, absorption coecient, sound absorbing or electroacoustic properties, arranged around an electronic panel that contains directional amplification and early/late acoustic response, the system adjusts its acoustic properties. circuit controls and sensing inputs. In response to the inputs, such as ideal reverberation time, In particular, resonant chamber modifies the acoustic performances of the space within which it is absorption coefficient, directional amplification and early/late acoustic response, the system adjusts installed by gross deformations of its shape, able to alter the aural volume, and by locally adjusting the its acoustic properties. In particular, resonant chamber modifies the acoustic performances of the folding configuration, to change the panels exposed to the sound waves. The optimal geometry and space within which it is installed by gross deformations of its shape, able to alter the aural volume, the characteristics of the materials were determined by acoustic simulations and measurements on and by locally adjusting the folding configuration, to change the panels exposed to the sound waves. physical prototypes [99–103]. The optimal geometry and the characteristics of the materials were determined by acoustic simulations and measurements on physical prototypes [99–103]. Acoustics 2020, 2 265 Acoustics 2020, 3 FOR PEER REVIEW 20 Figure 15. Resonant Chamber. Image courtesy RVTR © Adam Smith. Figure 15. Resonant Chamber. Image courtesy RVTR © Adam Smith. Courtyard Enclosure of Smithsonian Institute 2.2.1.16. Courtyard Enclosure of Smithsonian Institute Design and acoustics: Foster + Partners; Washington, DC, USA, 2007 Design The an design d acoustics of the : Fo courtyar ster + Pd artners; Wa enclosure shi fornthe gton, DC, Smithsonian USA, 20 Institute’s 07 Patent Oce, an historic building in Washington, was developed in the framework of an invited international competition, The design of the courtyard enclosure for the Smithsonian Institute’s Patent Office, an historic won by Foster + Partners. APBD informed the design of the courtyard enclosure, which is a complex building in Washington, was developed in the framework of an invited international competition, roof structure meant to perform at the same time as a solar shade, an acoustic absorber and a weather won by Foster + Partners. APBD informed the design of the courtyard enclosure, which is a complex protection device. The proposal consists of a glazed undulated canopy, which features a diagonal grid roof structure meant to perform at the same time as a solar shade, an acoustic absorber and a weather of structural beams and is supported by eight columns arranged in three domes (Figure 16). Since the protection device. The proposal consists of a glazed undulated canopy, which features a diagonal space underneath was meant to be flexible and hosts a variety of events, such as receptions, seated grid of structural beams and is supported by eight columns arranged in three domes (Figure 16). dinners and music and theatrical performances, the acoustic treatment was integrated in the bearing Since the space underneath was meant to be flexible and hosts a variety of events, such as receptions, structure of the canopy. The Specialist Modeling Group, a research team within Foster + Partners, seated dinners and music and theatrical performances, the acoustic treatment was integrated in the developed a custom generative script able to control the entire roof system based on a set of parameters, bearing structure of the canopy. The Specialist Modeling Group, a research team within Foster + allowing for exploration of a wide range of design alternatives. During the design process, the di erent Partners, developed a custom generative script able to control the entire roof system based on a set design goals were mutually related and synthesized by the generative tool, which was constantly of parameters, allowing for exploration of a wide range of design alternatives. During the design adapted as the design requirements became more specific. The acoustic performance goal was to process, the different design goals were mutually related and synthesized by the generative tool, reduce the reverberation time between 2 and 3.5 s. To this aim, the structural beams of the canopy which was constantly adapted as the design requirements became more specific. The acoustic were designed to work as sound absorbing devices. The sound absorbing layers of mineral wool performance goal was to reduce the reverberation time between 2 and 3.5 s. To this aim, the structural were mounted at the sides of the core steel structure of the beam and were covered by layer of thin beams of the canopy were designed to work as sound absorbing devices. The sound absorbing layers of mineral wool were mounted at the sides of the core steel structure of the beam and were covered by layer of thin steel tubes. The latter layer, while visually hiding the sound absorbing material, is Acoustics 2020, 2 266 Acoustics 2020, 3 FOR PEER REVIEW 21 steel tubes. The latter layer, while visually hiding the sound absorbing material, is “transparent” to sound, exposing the sound absorbing filling to the impinging sound waves. To provide the desired “transparent” to sound, exposing the sound absorbing filling to the impinging sound waves. To reduction of reverberation time, the area of the sound absorbing material was a key parameter in provide the desired reduction of reverberation time, the area of the sound absorbing material was a the generating algorithm. Although acoustic simulations were not integrated in the modeling tool, key parameter in the generating algorithm. Although acoustic simulations were not integrated in the the digital models of the enclosure could be easily exported to be analyzed in the external software. modeling tool, the digital models of the enclosure could be easily exported to be analyzed in the Ultimately, the final solution for the roof was the result of more 400 design iterations explored during a external software. Ultimately, the final solution for the roof was the result of more 400 design period of 6 months [104–107]. iterations explored during a period of 6 months [104–107]. Figure Figure 16. 16. Courtyar Courtyard Enclosu d Enclosur re e of Sm of Smithsonian ithsonian Institu Institute. te. Image Image cou courtesy rtesy © © Brady Brady Peter Peters. s. 2.2.2. Other Spaces 2.2.2. Other Spaces FabPod 2.2.2.1. FabPod Design and acoustics: Nick Williams, Brady Peters, John Cherrey, Jane Burry, Mark Burry, Design and acoustics: Nick Williams, Brady Peters, John Cherrey, Jane Burry, Mark Burry, Alexander Alexander Peña De León, Daniel Davis; Melbourne, Australia, 2013 Peña De León, Daniel Davis; Melbourne, Australia, 2013 The project is an acoustic enclosure for meetings, able to host eight people, housed in an open-plan oce at RMIT University (Figure 17). The FabPod project is part of a research investigating the The project is an acoustic enclosure for meetings, able to host eight people, housed in an open- sound di using properties of hyperboloid surfaces, which was previously explored on a prototype plan office at RMIT University (Figure 17). The FabPod project is part of a research investigating the wall in 2011. The acoustic design imperatives were to reduce the sound transmission through the sound diffusing properties of hyperboloid surfaces, which was previously explored on a prototype enclosure and to provide a homogeneous internal acoustics that was conductive to small meetings, wall in 2011. The acoustic design imperatives were to reduce the sound transmission through the without creating an acoustically “dead” space. In order to meet these objectives, the FabPod combines enclosure and to provide a homogeneous internal acoustics that was conductive to small meetings, sound absorption and sound di usion within the cell, creating a di use sound field by exploiting without creating an acoustically “dead” space. In order to meet these objectives, the FabPod combines the sound scattering properties of hyperboloid surfaces. A similar strategy was applied also to the sound absorption and sound diffusion within the cell, creating a diffuse sound field by exploiting the outer side of the installation, with the aim to improve the auditory experience in its surroundings. sound scattering properties of hyperboloid surfaces. A similar strategy was applied also to the outer The project is intended as a flexible structure, able to be applied to a range of scenarios, and therefore side of the installation, with the aim to improve the auditory experience in its surroundings. The project is intended as a flexible structure, able to be applied to a range of scenarios, and therefore great consideration was dedicated to fabrication quality and mass-customization. APBD was applied to the definition of the overall enclosure form and to the geometrical and material properties of the Acoustics 2020, 2 267 great consideration was dedicated to fabrication quality and mass-customization. APBD was applied Acoustics 2020, 3 FOR PEER REVIEW 22 to the definition of the overall enclosure form and to the geometrical and material properties of the surface pattern. Three material options were developed for the facets of the interior surface (plexiglass, surface pattern. Three material options were developed for the facets of the interior surface metal and felt), featuring di erent rates of absorption. The parametric model of the structure was (plexiglass, metal and felt), featuring different rates of absorption. The parametric model of the defined in Grasshopper and four di erent workflows were developed, each one using a di erent structure was defined in Grasshopper and four different workflows were developed, each one using acoustic simulation tool, to design either the enclosure form or the pattern of hyperboloid blocks. a different acoustic simulation tool, to design either the enclosure form or the pattern of hyperboloid Pachyderm Acoustics and Odeon, which are based on geometrical acoustics, were used to analyze the blocks. Pachyderm Acoustics and Odeon, which are based on geometrical acoustics, were used to form of the enclosure, and two custom wave-based acoustic simulation tools were used to simulate analyze the form of the enclosure, and two custom wave-based acoustic simulation tools were used the acoustic performance of the hyperboloid surfaces. Di erent acoustic parameters were taken into to simulate the acoustic performance of the hyperboloid surfaces. Different acoustic parameters were account, including reverberation time, sound pressure level, speech transmission index (STI) and the taken into account, including reverberation time, sound pressure level, speech transmission index scattering coecient. The final design consists in a semi-enclosed envelope, which wraps around the (STI) and the scattering coefficient. The final design consists in a semi-enclosed envelope, which meeting area and is composed by an irregular pattern of 180 unique hyperboloid blocks, featuring wraps around the meeting area and is composed by an irregular pattern of 180 unique hyperboloid di erent acoustic properties [108–113]. blocks, featuring different acoustic properties [108–113]. Figure 17. FabPod. Image courtesy © John Gollings. Figure 17. FabPod. Image courtesy © John Gollings. Manufacturing Parametric Acoustic Surfaces (MPAS) Project 2.2.2.2. Manufacturing Parametric Acoustic Surfaces (MPAS) project Design and acoustics: Brady Peters, Martin Tamke (CITA); Barcelona, Spain, 2010 The temporary project was installed at the Smart Geometry 2010 Workshop and Conference and Design and acoustics: Brady Peters, Martin Tamke (CITA); Barcelona, Spain, 2010 consists of a curved wall composted of di erent panel types, which generates di erent types of acoustic The temporary project was installed at the Smart Geometry 2010 Workshop and Conference and subspaces (Figure 18). The project explores new forms and material compositions and digital fabrication consists of a curved wall composted of different panel types, which generates different types of techniques. The APBD approach was applied to the design of the undulating from of the wall and to acoustic subspaces (Figure 18). The project explores new forms and material compositions and digital the panel composition. The design of the installation was developed in GenerativeComponents with fabrication techniques. The APBD approach was applied to the design of the undulating from of the the support of generative computer scripts, while acoustic simulations were run in Odeon. The acoustic wall and to the panel composition. The design of the installation was developed in goal was to create di erent acoustic subspaces in the surroundings of the installation: from a quiet, GenerativeComponents with the support of generative computer scripts, while acoustic simulations enclosed area, characterized by a high rate of sound absorption, to an amplified sound area, generated were run in Odeon. The acoustic goal was to create different acoustic subspaces in the surroundings by sound reflective surfaces, with a gradient of acoustic performance between the two conditions. of the installation: from a quiet, enclosed area, characterized by a high rate of sound absorption, to Such di erent acoustic performances could not be e ectively described by the reverberation time an amplified sound area, generated by sound reflective surfaces, with a gradient of acoustic alone; therefore, a number of other acoustic parameters were introduced in the analyses, such as early performance between the two conditions. Such different acoustic performances could not be decay time, speech transmission index and sound pressure level. Moreover, auralizations were used to effectively described by the reverberation time alone; therefore, a number of other acoustic parameters were introduced in the analyses, such as early decay time, speech transmission index and sound pressure level. Moreover, auralizations were used to listen to the sonic environments generated by the installation prior to its construction. The acoustic performances drove the design of both the overall shape of the installation and its panel composition. Nine panel types with different Acoustics 2020, 2 268 listen to the sonic environments generated by the installation prior to its construction. The acoustic Acoustics 2020, 3 FOR PEER REVIEW 23 performances drove the design of both the overall shape of the installation and its panel composition. Nine panel types with di erent acoustic performances were designed and opportunely integrated in acoustic performances were designed and opportunely integrated in manufacturing parametric manufacturing parametric acoustic surfaces (MPAS) in order to produce the desired acoustic e ects. acoustic surfaces (MPAS) in order to produce the desired acoustic effects. The collection of panel The collection of panel typologies includes a sound absorbing panel, di erent types of sound di using typologies includes a sound absorbing panel, different types of sound diffusing panels, variously panels, variously perforated screens, a panel with di erent properties depending on the direction of perforated screens, a panel with different properties depending on the direction of the impinging the impinging sound and a “sound window”, which provided visual connection from one acoustic sound and a “sound window”, which provided visual connection from one acoustic space to the space to the other. Based on acoustic performance feedbacks, the geometrical form of the wall and its other. Based on acoustic performance feedbacks, the geometrical form of the wall and its panel panel composition were controlled to generate the di erent acoustic subspaces in the surroundings of composition were controlled to generate the different acoustic subspaces in the surroundings of the the installation [104,114–116]. installation [104,114–116]. Figure 18. MPAS project. Image courtesy © Brady Peters. Figure 18. MPAS project. Image courtesy © Brady Peters. Distortion II 2.2.2.3. Distortion II Design and acoustics: Brady Peters, Martin Tamke, Stig Nielsen (CITA); Niels Jacubiak Andersen (Krydsrum); Magnus Gustafson and Patric Gustafson (Akustikmiljo)); Copenhagen, Denmark, 2011 Design and acoustics: Brady Peters, Martin Tamke, Stig Nielsen (CITA); Niels Jacubiak Andersen Distortion II is an experimental research project developed to create a bending acoustic surface (Krydsrum); Magnus Gustafson and Patric Gustafson (Akustikmiljo)); Copenhagen, Denmark, 2011 able to create visual and acoustic e ects within an open-plan space (Figure 19). The temporary structure Distortion II is an experimental research project developed to create a bending acoustic surface is composed by a folded surface, made of composite plates arranged in a series of trihedral corners able to create visual and acoustic effects within an open-plan space (Figure 19). The temporary with di erent dimensions and orientations. Four di erent digital production techniques were used structure is composed by a folded surface, made of composite plates arranged in a series of trihedral in the installation, i.e., laser cutting, knife cutting, CNC routing and metal bending, and fabrication corners with different dimensions and orientations. Four different digital production techniques files were generated by a custom tool. The installation explores the potentials of acoustic subspaces were used in the installation, i.e., laser cutting, knife cutting, CNC routing and metal bending, and (see also MPAS project) and creates a sound-amplified area and a sound-dampened zone. To this fabrication files were generated by a custom tool. The installation explores the potentials of acoustic aim, the APBD approach was applied to define the materials, the level of enclosure of the structure subspaces (see also MPAS project) and creates a sound-amplified area and a sound-dampened zone. and the geometry of the panels to control sound reflections. The acoustic parameters used to define To this aim, the APBD approach was applied to define the materials, the level of enclosure of the and measure the inhomogeneous acoustic space surrounding the installation were reverberation time, structure and the geometry of the panels to control sound reflections. The acoustic parameters used early decay time, sound strength and an experimental parameter (STV IA-di ) [117,118]. Two design to define and measure the inhomogeneous acoustic space surrounding the installation were workflows were used in the development of the project: in the first Odeon was used to run the reverberation time, early decay time, sound strength and an experimental parameter (STV IA-diff) [117,118]. Two design workflows were used in the development of the project: in the first Odeon was used to run the acoustic simulation, while in the second the acoustic analyses were directly run within the modeling environment using a custom ray-tracing tool, to provide instantaneous performance feedback for the optimization process. The latter workflow was only used in conceptual phases, while Acoustics 2020, 2 269 acoustic simulation, while in the second the acoustic analyses were directly run within the modeling environment using a custom ray-tracing tool, to provide instantaneous performance feedback for Acoustics 2020, 3 FOR PEER REVIEW 24 the optimization process. The latter workflow was only used in conceptual phases, while Odeon was extensively used in subsequent ones to accurately calculate the di erent acoustic parameters Odeon was extensively used in subsequent ones to accurately calculate the different acoustic considered. The plates that compose the installation feature opposite acoustic properties on their parameters considered. The plates that compose the installation feature opposite acoustic properties sides, being composed by a layer of sound absorbing material, a structural MDF panel and a layer on their sides, being composed by a layer of sound absorbing material, a structural MDF panel and a with a sound-reflective aluminum face. The arrangement and materials of the plates of the trihedral layer with a sound-reflective aluminum face. The arrangement and materials of the plates of the corners were optimized through an iterative routine to generate the two acoustic subzones. In the trihedral corners were optimized through an iterative routine to generate the two acoustic subzones. sound-amplified zone, the plates sides feature sound reflective properties and are arranged in order to In the sound-amplified zone, the plates sides feature sound reflective properties and are arranged in create focusing, while on the sound-dampened area, the faces of the plates feature sound absorptive order to create focusing, while on the sound-dampened area, the faces of the plates feature sound properties and their configuration promotes sound di usion [117,119]. absorptive properties and their configuration promotes sound diffusion [117,119]. Figure 19. Distortion II. Image courtesy © Anders Ingvartsen. Figure 19. Distortion II. Image courtesy © Anders Ingvartsen. 3. Discussion 3. Discussion The information regarding the design processes of the case studies is summarized in Figure 20, The information regarding the design processes of the case studies is summarized in Figure 20, where the case studies within the categories “music venues” and “other spaces” have been further where the case studies within the categories “music venues” and “other spaces” have been further classified in accordance to their architectural typologies. The table gathers information regarding the classified in accordance to their architectural typologies. The table gathers information regarding the primary functions, the design features developed with APBD, as well as ragarding the procedures and primary functions, the design features developed with APBD, as well as ragarding the procedures tools used in the development of the projects. and tools used in the development of the projects. Acoustics 2020, 2 270 Acoustics 2020, 3 FOR PEER REVIEW 25 Figure 20. The table o ers an overview of the projects, gathering relevant data on their architectural Figure 20. The table offers an overview of the projects, gathering relevant data on their architectural features and on the design development. features and on the design development. 3.1. Architecture and APBD 3.1. Architecture and APBD The collection of case studies shows a great degree of variation with respect to their functions The collection of case studies shows a great degree of variation with respect to their functions and profiles: from world-renowned concert halls to more ordinary architectures, research projects and and profiles: from world-renowned concert halls to more ordinary architectures, research projects artistic installations. and artistic installations. Most of case studies are major projects, such as concert halls venues, developed by renowned Most of case studies are major projects, such as concert halls venues, developed by renowned architectural firms and acoustic consulting groups, or were developed as research projects. In the first architectural firms and acoustic consulting groups, or were developed as research projects. In the first case, the resources and specialized expertise that are often available to major architectural firms, along case, the resources and specialized expertise that are often available to major architectural firms, with the reliance on external consultants, enable an innovative approach such as APBD to be e ectively along with the reliance on external consultants, enable an innovative approach such as APBD to be applied. However, such resources are generally not available in more ordinary projects, especially effectively applied. However, such resources are generally not available in more ordinary projects, when the architectural firms involved have no technical expertise on parametric modeling, acoustics especially when the architectural firms involved have no technical expertise on parametric modeling, and programming, as it is often the case. This result suggests that this procedure requires specialized acoustics and programming, as it is often the case. This result suggests that this procedure requires expertise and resources, which are not commonly available for ordinary architectural projects. specialized expertise and resources, which are not commonly available for ordinary architectural Most projects are spaces meant to host music performance (16 projects out of 19), while only a projects. small fraction of the projects is developed for other purposes (e.g., artistic installation, meeting room and multipurpose space). This suggest that the application of APBD is in line with the general trend of Acoustics 2020, 2 271 including acoustic concerns mainly in the development of spaces intended for music performances. However, certain projects, such as FabPod, Resonant Chamber and the Courtyard Enclosure of the Smithsonian Institution, shows the application of APBD for spaces intended for a wider variety of purposes. Across the collection, APBD has been applied to either major or minor architectural features of the design, ranging from reflectors and pattern textures in concert halls, to the overall shape of smaller architectures, such as acoustic shells or artistic installations. In the design of concert halls, the main structure of the venue is generally based on well-known typologies (e.g., shoe-box, vineyard, etc.), while APBD is applied to reflective surfaces or di usive pattern. In smaller intervention, such as pavilion and acoustic shells, APBD has been applied also to entirely shape the structures, often combining other goals, such as fabrication criteria. This highlights that PBD approach is often paired with a more conventional approach in large projects to better combine the large number of requirements, which need to be considered. 3.2. Digital Workflows in APBD APBD is normally applied due to the combined use of parametric modeling and acoustic performance simulation tools. Moreover, optimization tools can be exploited to automate the search of the most favorable solutions with respect to the target performance goals. The parametric modeling tool that was used in the great majority of the considered projects is Grasshopper [20] for Rhinoceros [21]. Acoustic analyses were mainly run using custom tools based on geometrical acoustics, while the commercial package that was used the most is Odeon [38]. In many cases, optimization tools based on evolutionary algorithms, such as Galapagos [24] and Octopus [25], have been utilized to support the design process. Parametric modeling eases the design optimization process, by allowing one to easily modify the design by controlling the model parameters. Grasshopper is one of the most commonly used parametric modeling tools. It is a graphical algorithm editor integrated in Rhinoceros, which is a commercial modeling tool widely employed in architectural practice. Grasshopper enables one to generate parametric models of complex geometries on the basis of algorithms set by the designer. Grasshopper does not require any programming knowledge and is therefore employed by designers with relative ease. Currently, a wide number of acoustic simulation tools, such as Odeon, CATT-Acoustic, etc., are available, allowing professionals to quickly perform simulations based on geometrical acoustic methods. Odeon is the commercial package that was more widely employed in the collected case studies. Acoustic simulation tools require a solid acoustic knowledge base to correctly set up the simulation and interpret its results. In most cases, the acoustic knowledge of architectural professionals is not adequate to correctly employ these systems, making the reliance on external acoustic consultants unavoidable. Another limitation is due to the lack of integration among simulation and modeling tools, which are generally stand-alone applications, and the limited interoperability resulting from the specific formats or geometrical models required to run the acoustic simulation. Some tools, such as the SketchUp plugin of Odeon [120], ease the file exchange between the modeling and simulation environments. However, the generation of specific model for acoustic analyses is often mandatory to meet the requirements of the simulation tools (e.g., geometrical simplification, watertight model and layer division by materials). Therefore, architectural design and acoustic performance analyses need to be run into two separated environments on specific virtual models, resulting in a time-consuming process, which often limits the number of model exchanges among professionals. As a result, design optimization in early design phases can be dicult to achieve from the feedback provided by these tools, which are more commonly used in late design phases for verification purposes, as shown in many case studies. A noteworthy exception in this frame is Pachyderm Acoustics [40], an open-source acoustic simulation tool integrated in Rhinoceros/Grasshopper, which was used in the development of FabPod. Acoustics 2020, 2 272 In many case studies custom tools were employed to avoid the issues resulting from the poor level of interoperability and to perform specific analyses. For instance, the use of custom tool has been reported in 16 out of 19 case studies. Such tools are generally used in early design phases to provide quick estimations of the acoustic performances directly in the modeling environment. Currently, di erent modeling platforms o er the possibility to the users to create custom programs (e.g., Rhinoscript, Grasshopper, Python, etc.) within their environment, widening the possibilities o ered by the regular preset functionalities. In most cases, custom tools have been used in early design phases to run simplified performance analyses, easily visualize the results and optimize the design proposal accordingly. By clarifying the relation between acoustic and architectural design, these tools support an e ective collaboration between architect and acousticians, and possibly the other technicians involved, enabling one to integrate di erent goals in the design proposal. Custom acoustic simulation tools are generally based on geometrical acoustic technique and apply ray-tracing or image-source methods. The performance feedback obtained, although simplified, is considered accurate enough to orient the design decision in early design phases. In many cases, more accurate analyses were run in late design phases with commercial acoustic simulation tools to further validate the results. Following a di erent approach, custom tools can be used to run sophisticated acoustic analyses, such as wave-based ones, which at the time of writing are not included in any commercial acoustic simulation package. In wave-based simulations, the wave behavior of sound phenomena, which are normally neglected in geometrical acoustic simulations, can be accurately simulated in 2D environments. For instance, in the development of FabPod, wave-based acoustic simulations were used to assess the scattering performance of the surfaces, which could not be accounted with geometrical acoustic techniques. Despite the wide range of possibilities o ered by custom tools, the programming skills and acoustic knowledge required in their development and application are normally not available to architectural firms. However, currently the availability of several online coding courses and of platforms such as ACOUCOU [121], which o ers free education materials on acoustics, may help to fill the gap. Furthermore, the introduction of PBD approach in architectural education would help students to become more familiar with building performance and simulation tools. Some of the case studies analyzed (e.g., ReS 6.0, Aalborg Acoustic Pavilions, MPAS project and Distortion II) were developed in an educational framework, and students were actively involved through summer schools and workshop; previous educational experiences with the PBD approach have been also documented in [16,17]. The design optimization can be performed either manually, for subsequent iterations by the operator, or in an automated matter. In the latter case, the parametric model is automatedly optimized on the basis of performance feedback until one or more satisfying solutions are achieved, resulting in a quick and ecient process. The support of automated processes has been reported in the development of most case studies (11 out of 19). The optimization tools that were used in the case studies analyzed are Galapagos and Octopus, which are based on evolutionary algorithms, and are directly integrated in Grasshopper for Rhinoceros. Such tools enable one to run either single objective or multiobjective optimization of parametric models defined in Grasshopper, based on target requirements and variation space set by the user. The performance feedbacks needed to set up the optimization process are generally obtained from the custom acoustic simulation tool integrated in the modeling environment. The design proposal can be optimized since early design phases based on the simplified performance feedbacks from the custom acoustic simulation tools, while more sophisticated simulation systems, such as Odeon, can be employed in late design phases when most design features have been already defined. These tools can be used to verify the performance of the preselected design proposals and provide the designers with detailed suggestions for further design improvements. For instance, commercial packages were used in late design phases to validation purposes in the Philharmonie de Paris, in the music venues in Fuzhou and in ReS 6.0. Acoustics 2020, 2 273 4. Conclusions As the impact of acoustic performances on human well-being are being acknowledged, acoustic concerns are expected to be increasingly integrated in the design of spaces with a variety of functions. In common practice, acoustic consultants are rarely involved since early design phases, and acoustic optimization and architectural design tend to be rather independent processes. In this frame, the application of performance-based design in acoustics seems very promising to optimize design proposals in light of performance feedbacks obtained from acoustic simulation tools. However, the method finds little application in current architectural practice, and is mainly restricted to notable architectures and research projects. A set of case studies developed with APBD has been collected in the attempt to shed some light on the state of the art of the application of the method in current architectural practice, evidence the design strategies followed and suggest some possible fields of improvement to further encourage its application. The development of integrated platforms that combine acoustic analyses and architectural modeling, the increased interoperability among modeling and simulation tools, would ease performance analyses in early design phases, and will allow for an e ective collaboration among architectural and acoustic specialists. The enhancement of acoustic and coding skills of designers, which can be promoted by the provision of specialized teaching platforms, would support the development and application of custom tools to run simplified analyses in the modeling environment during early design phases, hopefully encouraging the application of APBD in practice. Author Contributions: Conceptualization, L.S.; methodology, E.B., L.S. and A.A.; investigation, E.B.; resources, L.S. and A.A.; data curation, E.B.; writing—original draft preparation, E.B.; writing—review and editing, L.S. and A.A.; visualization, E.B.; supervision, L.S. and A.A. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors would like to thank the professionals that provided useful information to the authors on the design processes, and the copyright owners of the photographs that granted the permission to use the images in this work. Conflicts of Interest: The authors declare no conflict of interest. The information given on each project has been carefully obtained from publications and information available online. Any possible inaccurate information should be considered unintended and can be reported to the authors. References 1. Shi, X. Performance-based and performance-driven architectural design and optimization. Front. Arch. Civ. Eng. China 2010, 4, 512–518. [CrossRef] 2. Shi, X.; Yang, W. Performance-driven architectural design and optimization technique from a perspective of architects. Autom. Constr. 2013, 32, 125–135. [CrossRef] 3. Turrin, M.; Von Buelow, P.; Stou s, R. Design explorations of performance driven geometry in architectural design using parametric modeling and genetic algorithms. Adv. Eng. Inform. 2011, 25, 656–675. [CrossRef] 4. Grobman, Y.J.; Ron, R. Digital Form Finding: Generative use of simulation processes by architects in the early stages of the design process. In Proceedings of the 29th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Ljubljana, Slovenia, 21–24 Semptember 2011; pp. 107–115. [CrossRef] 5. Chong, Y.T.; Chen, C.H.; Leong, K.F. A heuristic-based approach to conceptual design. Res. Eng. Des. 2009, 20, 97–116. [CrossRef] 6. Wang, J. Improved engineering design concept selection using fuzzy sets. Int. J. Comput. Integr. Manuf. 2002, 15, 18–27. [CrossRef] 7. Méndez Echenagucia, T.; Capozzoli, A.; Cascone, Y.; Sassone, M. The early design stage of a building envelope: Multi-objective search through heating, cooling and lighting energy performance analysis. Appl. Energy 2015, 154, 577–591. [CrossRef] Acoustics 2020, 2 274 8. Lu, S.; Yan, X.; Li, J.; Xu, W. The influence of shape design on the acoustic performance of concert halls from the viewpoint of acoustic potential of shapes. Acta Acust. United Acust. 2016, 102, 1027–1044. [CrossRef] 9. Paulson, B.C., Jr. Designing to Reduce Construction Costs. J. Constr. Div. 1976, 102, 587–592. [CrossRef] 10. Marble, S. Digital Workflows in Architecture: Design–Assembly–Industry; Birkhauser: Basel, Switzerland, 2012. 11. Méndez Echenagucia, T. Computational Search in Architectural Design. Ph.D. Thesis, Polytechnic University of Turin, Turin, Italy, 2013. 12. Reinhardt, D.; Martens, W.L.; Miranda, L. Acoustic Consequences of Performative Structures—Modelling dependencies between spatial formation and acoustic behaviour. In Proceedings of the 30th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Prague, Czech Republic, 12–14 September 2012; pp. 577–586. 13. Becker, R. Fundamentals of performance-based building design. Build. Simul. 2008, 1, 356–371. [CrossRef] 14. Hensel, M. Performance-Oriented Architecture: Rethinking Architectural Design and the Built Environment; John Wiley & Sons: Hoboken, NJ, USA, 2013. [CrossRef] 15. Kolarevic, B.; Malkawi, A. Performative Architecture: Beyond Instrumentality; Routledge: Abingdon-on-Thames, UK, 2005. [CrossRef] 16. Holzer, D. Design exploration supported by digital tool ecologies. Autom. Constr. 2016, 72, 3–8. [CrossRef] 17. Jensen, M.B. Robotic Fabrication of Acoustic Geometries—An explorative and creative design process within an educational context. ArchiDOCT 2019, 6, 34–45. 18. Oxman, R. Performance-Based Design: Current Practices and Research Issues. Int. J. Arch. Comput. 2008, 6, 1–17. [CrossRef] 19. Oxman, R. Theory and design in the first digital age. Des. Stud. 2006, 27, 229–265. [CrossRef] 20. Rutten, D. Grasshopper. Available online: http://www.grasshopper3d.com/ (accessed on 18 March 2020). 21. Rhinoceros. Available online: http://www.rhino3d.com/ (accessed on 18 March 2020). 22. GenerativeComponents. Available online: https://www.bentley.com/en/products/product-line/modeling- and-visualization-software/generativecomponents (accessed on 18 March 2020). 23. Flager, F.; Haymaker, J. A comparison of multidisciplinary design, analysis and optimization processes in the building construction and aerospace industries. In Proceedings of the 24th W78 Conference, Maribor, Slovenia, 27–29 June 2007; pp. 625–630. [CrossRef] 24. Rutten, D. Galapagos. Available online: http://www.grasshopper3d.com/group/galapagos (accessed on 18 March 2020). 25. Vierlinger, R. Octopus. Available online: http://www.food4rhino.com/app/octopus (accessed on 18 March 2020). 26. Tang, M.; Anderson, J.; Aksamija, A.; Hodge, M. Performace-based Generative Design: An investigation of the parametric nature of architecture. In Proceedings of the 100th Association of Collegiate Schools of Architecture (ACSA) Annual Meeting, Boston, MA, USA, 1–4 March 2012; Volume 2, pp. 1–8. 27. Bassuet, A.; Rife, D.; Dellatorre, L. Computational and Optimization Design in Geometric Acoustics. Build. Acoust. 2014, 21, 75–85. [CrossRef] 28. Takenaka, T.; Okabe, A. A Computational Method for Integrating Parametric Origami Design and Acoustic Engineering. Comput. Perform. 2013, 2, 289–296. 29. World Health Organization. Environmental Noise Guidelines for the European Region. 2018. Available online: http://www.euro.who.int/en/publications/abstracts/environmental-noise-guidelines-for- the-european-region-2018 (accessed on 18 March 2020). 30. Di Blasio, S.; Shtrepi, L.; Puglisi, G.E.; Astolfi, A. A Cross-Sectional Survey on the Impact of Irrelevant Speech Noise on Annoyance, Mental Health and Well-being, Performance and Occupants’ Behavior in Shared and Open-Plan Oces. Int. J. Environ. Res. Public Health 2019, 16, 280. [CrossRef] 31. Reinten, J.; Braat-Eggen, P.E.; Hornikx, M.; Kort, H.S.M.; Kohlrausch, A. The indoor sound environment and human task performance: A literature review on the role of room acoustics. Build. Environ. 2017, 123, 315–332. [CrossRef] 32. Badino, E.; Manca, R.; Shtrepi, L.; Calleri, C.; Astolfi, A. E ect of façade shape and acoustic cladding on reduction of leisure noise levels in a street canyon. Build. Environ. 2019, 157, 242–256. [CrossRef] 33. ISO 3382-1:2009. Acoustics—Measurement of room acoustic parameters. Part 1: Performance spaces. Int. Organ. Stand. 2009. Available online: https://www.iso.org/standard/40979.html (accessed on 18 March 2020). Acoustics 2020, 2 275 34. ISO 3382-2:2009. Acoustics—Measurement of room acoustics parameters. Part 2: Reverberation time in ordinary rooms. Int. Organ. Stand. 2009. Available online: https://www.iso.org/standard/36201.html (accessed on 18 March 2020). 35. Shtrepi, L.; Astolfi, A.; D’Antonio, G.; Guski, M. Objective and perceptual evaluation of distance-dependent scattered sound e ects in a small variable-acoustics hall. J. Acoust. Soc. Am. 2016, 140, 3651–3662. [CrossRef] 36. Bo, E.; Astolfi, A.; Pellegrino, A.; Pelegrin-Garcia, D.; Puglisi, G.E.; Shtrepi, L.; Rychtarikova, M. The modern use of ancient theatres related to acoustic and lighting requirements: Stage design guidelines for the Greek theatre of Syracuse. Energy Build. 2015, 95, 106–115. [CrossRef] 37. Cox, T.J.; D’Antonio, P. Acoustic Absorbers and Di users: Theory, Design and Application; Spon Press: London, UK, 2004. 38. Odeon. Available online: http://odeon.dk/ (accessed on 18 March 2020). 39. CATT-Acoustic. Available online: https://www.catt.se/ (accessed on 18 March 2020). 40. Van der Harten, A. Pachyderm Acoustics. Available online: http://www.perspectivesketch.com/pachyderm/ (accessed on 18 March 2020). 41. Lokki, T.; Southern, A.; Siltanen, S.; Savioja, L. Acoustics of epidaurus—Studies with room acoustics modelling methods. Acta Acust. United Acust. 2013, 99, 40–47. [CrossRef] 42. Shtrepi, L.; Hamilton, B.; Astolfi, A.; Masoero, M. Preliminary results of scattering surface modeling and perceptual aspects in wave-based acoustic simulations. In Proceedings of the 23rd International Congress on Acoustics, Aachen, Germany, 9–13 September 2019; pp. 5990–5993. [CrossRef] 43. Orazio, D.D.; Fratoni, G.; Rovigatti, A.; Hamilton, B. Numerical simulations of Italian opera houses using geometrical and wave-based acoustics methods. In Proceedings of the 23rd International Congress on Acoustics, Aachen, Germany, 9–13 September 2019; pp. 5994–5996. 44. Lu, S.; Yan, X.; Xu, W.; Chen, Y.; Liu, J. Improving auditorium designs with rapid feedback by integrating parametric models and acoustic simulation. Build. Simul. 2016, 9, 235–250. [CrossRef] 45. Negendahl, K. Building performance simulation in the early design stage: An introduction to integrated dynamic models. Autom. Constr. 2015, 54, 39–53. [CrossRef] 46. Mirra, G.; Pignatelli, E.; Di Rosario, S. An automated design methodology for acoustic shells in outdoor concerts. In Proceedings of the Euronoise, Crete, Greece, 27–31 May 2018; pp. 2123–2130. 47. Peters, B. Parametric Acoustic Surfaces. In reForm(), Proceedings of the Association for Computer Aided Design in Architecture 2009 Conference, Chicago, USA, 22–25 Octorber 2009; Sterk, T.D.E., Loveridge, R., Pancoast, D., Eds.; pp. 174–181. Available online: https://adk.elsevierpure.com/en/publications/parametric-acoustic-surfaces (accessed on 18 March 2020). 48. Peters, B. Integrating Acoustic Analysis in the Architectural Design Process using Parametric Modeling; Forum Acusticum: Aalborg, Denmark, 2011; pp. 1589–1594. 49. Wortmann, T.; Tunçer, B. Di erentiating parametric design: Digital workflows in contemporary architecture and construction. Des. Stud. 2017, 52, 173–197. [CrossRef] 50. Scopus. Available online: https://www.scopus.com (accessed on 18 March 2020). 51. Research Gate. Available online: https://www.researchgate.net/ (accessed on 18 March 2020). 52. Alias System Corporation; Autodesk, Autodesk Maya. Available online: https://www.autodesk.com/ products/maya/overview (accessed on 18 March 2020). 53. Day, C.; Marshall, H.; Scelo, T.; Valentine, J.; Exton, P. The Philharmonie de Paris—Acoustic design and commissioning. Proceedings of Acoustics 2016: The Second Australasian Acoustical Societies Conference, Brisbane, Australia, 9–11 November 2016; pp. 1–15. 54. McGar, J. The Acoustic Feats of the World’s Costliest Concert Hall. 2015. Available online: https: //sourceable.net/acoustic-feats-worlds-costliest-concert-hall/ (accessed on 18 March 2020). 55. Philharmonie de Paris. Available online: http://www.nagata.co.jp/e_sakuhin/factsheets/PdP.pdf (accessed on 18 March 2020). 56. Marshall, H. Implementing the acoustical concept for the Philharmonie de Paris, Grande Salle. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; Volume 37, Pt 3, pp. 118–127. 57. Kahle, E.; Wulfrank, T.; Jurkiewicz, Y.; Faillet, N. Philharmonie de Paris—The Acoustic Brief. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; Volume 37, Pt 3, pp. 105–110. Acoustics 2020, 2 276 58. Scelo, T. Integration of acoustics in parametric architectural design. Acoust. Aust. 2015, 43, 59–67. [CrossRef] 59. Philharmonie de Paris—Information Sheet. Available online: http://www.kahleacoustics.com/en/ref/ philharmonie.html# (accessed on 18 March 2020). 60. Khan, N. An Algorithm Designed a Hamburg Concert Hall’s Interior, Creating the Ideal Acoustic Experience. 2017. Available online: https://qz.com/894929/an-algorithm-designed-a-hamburg-concert-halls-interior- creating-the-ideal-acoustic-experience/ (accessed on 18 March 2020). 61. Elbphilharmonie Hamburg Grosser Saal. Available online: http://www.nagata.co.jp/e_sakuhin/factsheets/ Elbphilharmonie.pdf (accessed on 18 March 2020). 62. Stinson, E. What Happens When Algorithms Design a Concert Hall? The Stunning Elbphilharmonie. 2017. Available online: https://www.wired.com/2017/01/happens-algorithms-design-concert-hall-stunning- elbphilharmonie/ (accessed on 18 March 2020). 63. Oguchi, K. Highlights of Room Acoustics and Sound Isolation Design. 2017. Available online: http: //www.nagata.co.jp/e_news/news1702-e.html (accessed on 18 March 2020). 64. Architectural Details: Herzog & de Meuron’s Spectacular Elbphilharmonie. 2016. Available online: https: //architizer.com/blog/architectural-details-herzog-de-meuron-elbphilharmonie/ (accessed on 18 March 2020). 65. Mommertz, E.; Kahle, E. The Bochum Concert Hall—The challenge of small concert halls for large orchestras on low budget. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Cardiff, UK, 4–6 October 2018; Volume 40, Pt 1, pp. 174–181. 66. Anneliese Brost Musikforum Ruhr. Available online: https://www.architonic.com/en/project/bez-kock- architekten-anneliese-brost-musikforum-ruhr/5106249 (accessed on 18 March 2020). 67. Musikzentrum Bochum—Information Sheet. Available online: http://www.khale.be/en/ref/bochum.html# (accessed on 18 March 2020). 68. Nishiyama, Y. Miura folding: Applying Origami to space exploration. Int. J. Pure Appl. Math. 2012, 79, 269–279. 69. Ureshino Cultural Center. 2014. Available online: http://www.suep.jp/Ureshino_cultural_center/text_inE. html (accessed on 18 March 2020). 70. @Last Software; Google, SketchUp. Available online: https://www.sketchup.com/ (accessed on 18 March 2020). 71. Autodesk Revit. Available online: http://www.autodesk.com/revit (accessed on 18 March 2020). 72. Garber, R. Workflows: Expanding Architecture’s Territory in the Design and Delivery of Buildings; John Wiley & Sons: Hoboken, NJ, USA, 2017. 73. Theatroacoustic System for University of Iowa Concert Hall. Available online: https://lmnarchitects.com/ case-study/theatroacoustic-system-concert-hall (accessed on 18 March 2020). 74. Cornachio, J. Behind the Building: Voxman Music Building by LMN Architects. Available online: https: //architizer.com/blog/practice/materials/behind-voxman-music-building/ (accessed on 18 March 2020). 75. Jurkiewicz, Y.; Wulfrank, T.; Kahle, E. Architectural shape and early acoustic eciency in concert halls (L). J. Acoust. Soc. Am. 2012, 132, 1253–1256. [CrossRef] 76. Jurkiewicz, Y.; Moller, H.; Wulfrank, T.; Wang, J.; Kahle, E. Acoustic Optimization of Curved Architecture in Practice: The New Straight Cultural Arts Center in Fuzhou. In Proceedings of the International Symposium on Room Acoustics, Amsterdam, Netherlands, 15–17 September 2019; pp. 401–408. 77. Wulfrank, T.; Jurkiewicz, Y.; Kahle, E. Design-Focused Acoustic Analysis of Curved Geometries using a Di erential Raytracing Technique. Build. Acoust. 2014, 21, 87–96. [CrossRef] 78. García Gòmez, J.Ó.; Kahle, E.; Wulfrank, T. Shaping concert halls. In Proceedings of the EuroRegio, Porto, Portugal, 13–15 June 2016. 79. CATIA. Available online: http://www.3ds.com/products-services/catia/ (accessed on 18 March 2020). 80. Square One Research; Autodesk, Ecotect Analysis. Available online: https://www.autodesk.com/education/ free-software/ecotect-analysis (accessed on 18 March 2020). 81. Minutillo, J. When the Whole Is Greater Than the Sum of Its Parts. 2009. Available online: https://continuingeducation.bnpmedia.com/courses/areditorial/when-the-whole-is-greater-than- the-sum-of-its-parts/ (accessed on 18 March 2020). 82. The Conga Room/Belzberg Architects. 2011. Available online: http://www.archdaily.com/160584/the-conga- room-belzberg-architects (accessed on 18 March 2020). 83. Conga Room at LA Live. Available online: http://belzbergarchitects.com/project/conga-room/ (accessed on 18 March 2020). Acoustics 2020, 2 277 84. The Conga Room, Los Angeles. Available online: http://www.designcurial.com/projects/the_conga_room_ los_angeles (accessed on 18 March 2020). 85. Dynamo. Available online: http://dynamobim.org/ (accessed on 18 March 2020). 86. Fang, D. Shells for the Senses: The Multidisciplinary Success of Stage by the Sea. 2016. Available online: https://formfindinglab.wordpress.com/2016/09/21/shells-for-the-senses-the-multidisciplinary- success-of-stage-by-the-sea/ (accessed on 18 March 2020). 87. Flanagan, J. Acoustic Shells. Shotcrete 2015, 17, 16–19. 88. Griths, A. Shell-Shaped Shelter by Flanagan Lawrence Built on Littlehampton Seafront. 2014. Available online: https://www.dezeen.com/2014/07/22/flanagan-lawrence-acoustic-shells-shelter-stage-littlehampton/ (accessed on 18 March 2020). 89. Flanagan Lawrence—Acoustic Shells. Available online: https://theplan.it/eng/webzine/the-plan-award-2015/ acoustic-shells#sthash.XmPPnnkv.dpbs (accessed on 18 March 2020). 90. Acoustic Shells. Available online: http://flanaganlawrence.com/project/acoustic-shells/ (accessed on 18 March 2020). 91. Soundforms. Available online: https://www.flanaganlawrence.com/soundforms (accessed on 18 March 2020). 92. The Park’s Bandstand—A Built Environment Story. Available online: http://www.beyond2012.org.uk/ sounforms-the-parks-bandstand/ (accessed on 18 March 2020). 93. Bavister, P. Soundforms. (n.d.) 405–421. Available online: https://www.academia.edu/6385238/The_design_ development_and_fabrication_of_a_11_scale_mobile_acoustic_performance_shell_prototype (accessed on 28 April 2020). 94. Boning, W.; Acoustics, A.; Bassuet, A.; Rise, T.; Shell, G. A Room Without Walls: Optimizing an Outdoor Music Shell To Maintain Views and Maximize Reflections. In Proceedings of the Institute of Acoustics; Institute of Acoustics (IOA): Paris, France, 29–31 October 2015; pp. 332–341. 95. Foged, I.W.; Pasold, A.; Brath, M. Acoustic Environments: Applying Evolutionary Algorithms for Sound Based Morphogenesis. In Proceedings of the 30th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Prague, Czech Republic, 12–14 September 2012; pp. 347–353. 96. Furuto, A. Acoustic Environments/AREA and Electrotexture Lab. 2011. Available online: https://www. archdaily.com/170078/acoustic-environments-area-and-electrotexture-lab (accessed on 18 March 2020). 97. Foged, I.W.; Pasold, A.; Jensen, M.B. Evolution of an Instrumental Architecture. In Proceedings of the 32nd Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Newcastle upon Tyne, UK, 10–12 Semptember 2014; pp. 365–372. 98. Piker, D. Kangaroo. Available online: http://kangaroo3d.com/ (accessed on 18 March 2020). 99. Resonant Chamber. Available online: http://www.rvtr.com/projects/resonant-chamber (accessed on 18 March 2020). 100. Anderson, L. Origami in Stereo: Welcome to the Sound Cloud! Available online: https://architizer.com/blog/ resonant-chamber-rvtr/ (accessed on 18 March 2020). 101. Filipetti, J. Rvtr: Resonant Chamber Origami Architectural Acoustic Panels. Available online: http://www. designboom.com/technology/rvtr-resonant-chamber-origami-architectural-acoustic-panels/ (accessed on 18 March 2020). 102. Grozdanic, L. Resonant Chamber Is An Acoustically Responsive Envelope. Available online: http://www.evolo. us/architecture/resonant-chamber-is-an-acoustically-responsive-envelope/ (accessed on 18 March 2020). 103. Thün, G.; Velikov, K.; Ripley, C.; Sauvé, L.; McGee, W. Soundspheres: Resonant Chamber. Leonardo 2012, 45, 348–357. [CrossRef] 104. Peters, B. Acoustic Performance as a Design Driver: Sound Simulation and Parametric Modeling using SmartGeometry. Int. J. Arch. Comput. 2011, 8, 337–358. [CrossRef] 105. Peters, B. The Smithsonian Courtyard Enclosure: A case-study of digital design processes. Acadia 2007, 2007, 74–83. 106. Smithsonian Institution. Available online: http://www.bradypeters.com/smithsonian.html (accessed on 18 March 2020). 107. Smithsonian Selects Norman Foster to Design New Atrium for Historic Home of two Museum. Available online: https://www.fosterandpartners.com/news/archive/2004/03/smithsonian-selects-norman-foster-to- design-new-atrium-for-historic-home-of-two-museums/ (accessed on 18 March 2020). Acoustics 2020, 2 278 108. Williams, N.; Burry, J.; Davis, D.; Peters, B.; Pena De Leon, A.; Burry, M. FabPod: Designing with temporal flexibility & relationships to mass-customisation. Autom. Constr. 2015, 51, 124–131. [CrossRef] 109. Williams, N.; Davis, D.; Peters, B.; Pena de Leon, A.; Burry, J.; Burry, M. Fabpod: An open design-to-fabrication system. In Proceedings of the 18th International Conference on Computer-Aided Architectural Design Research in Asia (CAADRIA 2013), Singapore, 2013; pp. 251–260. 110. Burry, J.; Williams, N.; Cherrey, J.; Peters, B. Fabpod: Universal Digital Workflow, Local Prototype Materialization. In Proceedings of the 15th International Conference on Computer-Aided Architectural Design Futures, Shanghai, China, 3–5 July 2013; pp. 176–186. 111. Burry, M. FabPod. Available online: https://mcburry.net/fabpod/ (accessed on 18 March 2020). 112. Davis, D. FabPod. Available online: https://www.danieldavis.com/fabpod/ (accessed on 18 March 2020). 113. Peters, B. Integrating acoustic simulation in architectural design workflows: The FabPod meeting room prototype. Simulation 2015, 91, 787–808. [CrossRef] 114. Wong, K. Shaped by Number. 2010. Available online: http://www.cgw.com/Publications/CGW/2010/Volume- 33-Issue-9-October-2010-/Shaped-by-Number.aspx (accessed on 18 March 2020). 115. Peters, B. Complex Surfaces—Sound and Space Defining Surfaces for Architecture. Available online: https: //kadk.dk/case/complex-surfaces-sound-and-space-defining-surfaces-architecture (accessed on 18 March 2020). 116. Manufacturing Parametric Acoustic Surfaces. Available online: http://www.bradypeters.com/smartgeometry- 2010.html (accessed on 18 March 2020). 117. Peters, B.; Tamke, M.; Nielsen, S.A.; Vestbjerg Andersen, S.; Haase, M. Responsive Acoustic Surfaces, in: Respect. In Proceedings of the 29th Education and research in Computer Aided Architectural Design in Europe (eCAADe) Conference, Ljubljana, Slovenia, 21–24 Semptember 2011; pp. 819–828. 118. Pelegrín-García, D. Comment on “Increase in voice level and speaker comfort in lecture rooms” [J. Acoust. Soc. Am. 125, 2072–2082 (2009)] (L). J. Acoust. Soc. Am. 2011, 129, 1161–1164. [CrossRef] 119. Project Distortion II. Available online: http://www.bradypeters.com/project-distortion-ii.html (accessed on 18 March 2020). 120. SU2Odeon Plugin for SketchUp. Available online: https://odeon.dk/downloads/su2odeon/ (accessed on 18 March 2020). 121. ACOUCOU. Available online: https://acoucou.org/ (accessed on 18 March 2020). © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Journal

AcousticsMultidisciplinary Digital Publishing Institute

Published: May 1, 2020

Keywords: performance-based design; acoustic design; digital workflow; architectural design; design optimization; form-finding

There are no references for this article.