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Tuned Surfaces Incorporating Digital Simulation and Physical Prototyping in the Design of Acoustically Performative Side Wall Panels

Document Prepared by Philip Bussey

Acknowledgments This research was undertaken as a joint venture between the University of Minnesota’s School of Architecture and HGA as a pilot research internship by Philip Bussey for the Master’s of Science in Research Practice. This project wouldn’t have happened without Renee Cheng realizing the connection between the research that Marc Swackhamer and myself had been working on and how it could be incorporated in HGA’s practice. I’m also thankful for Marc’s input and help throughout the process by helping me prepare for my presentations to HGA and sharing his expertise in digital fabrication. I’m also grateful for the guidance of my supervisors at HGA; Amy Duoma, Rob Good, Jim Moore, and Alex Terzich. Our weekly check-ins helped to constantly make sure the research direction was mutually beneficial to HGA and the University of Minnesota. The project team members (Andrew Dull, Steve Philippi, Daniel Yudchitz, and Jesse Zeien) of Northrop Auditorium and the Ordway Performing Arts Center were always very accommodating to my many requests for information on those projects. It was extremely difficult coming into this process with very little knowledge on architectural acoustics. We wouldn’t have been able to make the progress we did on this project without the crash course in acoustics provided by Joshua Cushner of ARUP and Paul Scarborough of Akustiks. Their help along with the input from Ron Sauros of NWAA labs, Jeff Madison of RPG Diffusors, and David Berg of Orfield Laboratories was critical during the exploration into the design of the sidewall panel. Peter D’Antonio’s writings on acoustical diffusers were also instrumental as we designed different surfaces

This document exists in a digital format in the HGA project folder listed below: O:\Research Initiative\5. Research Projects\UM Research Consortium 2013\ Performative Surfaces

Abstract In contemporary architectural discourse, focus has expanded from “making form” to “finding form.” In form-finding, geometry grows out of a careful analysis of building program, user behavior and other “performative” standards such as sound. Architectural acoustics are an important characteristic in many of the spaces that we inhabit, but the tools and processes for designing acoustically-optimized spaces aren’t developed and documented as thoroughly as other dynamic natural phenomena like light. Phase one of the research involved a survey of published literature on architectural acoustics and interviews of the architectural and acoustical design team of the Ordway Center of the Performance Arts and Northrop Auditorium. Information from these sources was combined to evaluate the current state of practice for the use of computer simulations, the representation of acoustical data, and physical mock-ups in the design of acoustically driven surfaces. At the end of this phase, a workflow was proposed that architects could use to design a surface whose geometry is determined by its desired acoustic performance. The second phase of the research involved testing that process in the design of a diffusing side wall panel. Two issues were identified as the work progressed that necessitated a modification to the original workflow developed during the first phase of the research if this process was going to be applicable to architectural practice. These issues were; the need to design the manufacturing process for the panel in order to make the varied geometry more economical and the need to incorporate acoustical testing of the panel to verify the diffusive performance of the designed panels. The study concluded with a modified workflow that incorporated lessons learned through the prototyping process as well as a physical artifact that demonstrated what an acoustically optimized surface could look like.

Table of Contents



Research Methods


Case Study


Sidewall Panel Study






Introduction We are in the middle of a paradigm shift in architectural design. The proliferation of digital design skills, software and programming literacy, and computing power of our personal computers are converging to create a shift in the traditional design process. From an exercise of (1) form generation, (2) simulation and evaluation of performance and (3) aesthetic evaluation, the industry if shifting to processes that use simulation as the primary form generator that is then evaluated for its aesthetics (Oxman). In order to understand what sort of criteria and parameters need to be built into the simulation model, there are two thoughts on what the role the designer assumes with respect to their ownership and control of the data. One approach suggests a model of collaboration where the designer is in constant dialog with consultants to refine and perfect the digital model (Oxman). A second approach suggests that designers “only truly understand that which they create,� (Vrachliotis). This alternative method places the architect in a position of much more control over the data and tools that are creating the simulations. A culture of modifying the software tools has emerged around this second theory. In acoustic design, there has existed a culture of improvosation to create processes that replicate the physical phenomena of sound that couldn’t be approximated with the mathematical models of the time. In auditoria design during the 1910s, water tanks were built by scientists and the ripples were measured to simulate the wave behavior of sound (Rindel) previous to the use of the boundary element method of mathematical approximation (Cox). The analysis of room acoustics has been done by specialty architectural acoustical consulatants using computer simulations since the late 1960s (Rindel). Commercially available software has evolved over the years to provide sophisticated whole room acoustical analysis that can provide auralization of a room during the design process. These simulations still rely on vector approximations of space, which ignores diffusive effects of non-planar geometry and instead uses a coefficient to approximate that effect (Rindel). This limits the ability of the architectural consultant to take into account diffusion in their whole room analysis models that are primarily used to speculate on the acoustical behavior of a space before it is built. However, the process of analyzing acoustical surfaces still lies in the purview of the acoustician instead of the designer. This has led acousticians to develop products that have been optimized to deflect sound in ways specific 1

to their design criteria (D’Antonio). In order to create more conceptually and aesthetically consistent architecture (that still performs the way a performance hall needs to), the designer needs to understand what tools their consultants are using and integrate them within their workflow to be able evaluate their architecture earlier on in the process and iterate on the performance data that is given by those tools. The families of self-made plugins that have been developed by designers generally fall into two categories: analysis and form-finding. Examples of analytic plugins include Pachyderm (van der Harten), developed for the 3d modeling software Rhinoceros. By integrating the analysis into the same software, the designer can iterate more quickly with acoustical considerations in mind. However, in order to fully realize the potential of sound as a generative force and to fully understand it as a system, one must build a digital network that uses sound particles to define the architectural expression. One work that seeks to achieve this is currently being undertaken by LMN’s Tech Studio (Crawford). His work reverse engineers a surface geometry from a preferred diffusion pattern by using the ray-tracing method from a single source. This approach simplifies sound to a level where each portion of a surface is being ‘hit’ by a single ray of sound, which has gone too far to reduce the complexity of sound digitally in an attempt to use it as a form finding physical phenomena. LMN’s (as yet unpublished) next steps include making physical prototypes of the different surface scattering patterns that they’ve tested digitally and verify their performance through the use of a goniometer mounted with a speaker and receiver that measures decibels at different orientations to the surface to be tested. This test will go a long way to verify how effective the ray-tracing method is to measuring sound scattering and diffusion. One aspect of these simulation driven formal exercises that tend to limit their application to full scale building projects instead of small, art installation, scale projects is cost of fabrication. These form generation models tend to suggest surfaces with a high degree of gradated variation, typically called a topographical surfaces (Sheil). These topographical surfaces, when rationalized into a construction unit, often require a unique surface geometry for each of those units. While most research on creating economical variation in architecture has to do with subtractive processes (primarily through CNC milling), there’s an emerging body of work that looks at how different

forming processes, which are inherently more cost effective than milling manufacturing processes, like concrete casting and thermo-forming can be done in a way that allows for variation. The next step in creating formal variation through casting and forming processes is to make a connection between performance characteristics and the amount and type of surface modulation. The VarVac Wall in the School of Architecture’s office at the University of Minnesota aims to create a surface with varying diffusive characteristics along it with pockets of acoustical absorption in areas of high vocal activity (Swackhamer). In order to make that surface, the manufacturing process was modified in a way that all of the different surface geometries could be made with one reconfigurable mold. The constraints of this mold were plugged into a parametric process that would take a gradient image that represented variable acoustical performance and translate it into different panel geometries that could be created with that mold. While this research makes an important step to incorporate economic manufacturing into the design of performance driven surfaces, there are two components that need to be researched further before these ideas can be fully embraced by architectural practice. The first research topic would look at how data is understood in the current design process. The roll of consultants and simulation software would need to be studied to see who owns the data and how it could most productively be acted on to derive architectural forms. The second topic would look at how fabricators could be brought onto a project to determine how variation could be incorporated into their processes in an economical way so that these panels could be produced in a quantity necessary for building construction. This research collaboration between HGA and the University of Minnesota aims to answer some of these questions through a study of two performing arts projects and the design of a diffusing sidewall panel.


Research Methods In our attempt to understand how to design with acoustical data, we focused our study on two parallel investigations. One was a case study of two ongoing HGA performance hall projects, and the other was a design exercise looking at how an architect can be more involved in the design of diffusing side wall panels. Information that was learned through each of the two studies influenced the other throughout the project. For instance, the design criteria and geometric constraints of the sidewall panels from Ordway were used as the initial design parameters for the design exercise portion of the study. HGA Case Study A study of two local ongoing projects (Ordway Concert Hall and Northop Auditorium) that have demanding acoustical design criteria was done. This study involved interviews with the project architects and representatives of the acoustical consultants for both projects. The interview questions focused on identifying what the specific surfaces were that had to be designed with acoustical considerations, what the process was for communicating the acoustical information to the architects at HGA, and what sort of simulation tools were used to carry out the analysis. A taxonomy of acoustical strategies was created to give an understanding of how sound was dealt with at its different scales, and comparative drawings were created to represent the geometry of sound waves in order to understand how the different strategies specifically respond to those waves. Historical and precedent research was done to understand the current state of how digital simulation software is used in acoustical analysis and form finding. Acoustical design guides that were mentioned by the acousticians in the above interviews were consulted to understand what the underlying mathematical models were for the different simulation methods. Digital design, architectural simulation and acoustical journals were also surveyed to gain an understanding of how acousticians and architects are building on parametric design tools with the goal of giving the designer the ability to receive real time feedback during the design process. This will allow designers to iterate more productively with respect to acoustical performance. These different tools were compared in a matrix with respect to cost, modeling and interoperability capabilities, open or closed source software, the underlying mathematical models that they use to simulate sound, and what form the outputs took (graphics, auralization, etc.). 5

Data about the flow of information in the design process, the acoustical surface strategies, and the different tools that exist for designers and acousticians were combined to create a design process that allowed for more productive iteration and evaluation by the architectural design team. With the goal being that they would be able to engage with acousticians on the design of performance hall spaces in a more proactive manner. These design processes were evaluated by the architect and acoustical consultants based on ease of implementation in practice, reliability of analysis used by the designer, and respectfulness of existing professional obligations.

Sidewall Panel Study The goal of the second phase of research was to built a digital tool which would give acoustical feedback to the architect and would also be used to propose acoustically performative sidewall geometries based on the fabrication constraints related to thermoforming. As a way of testing the feasibility of our process, we would take the sidewall of a generic shoebox volume (common in performing arts projects), and use our plugin to create an acoustical map and articulated surface geometry. The criteria for the surface was determined through a series of conversations that the research team had with our acoustical consultant. We also revisited the previous study of commercially available and bespoke acoustical software to see what new functionality would be most beneficial to the architectural acoustics field to add. We decided that we would use the difference between the travel time of direct and reflected sound (using a reverberation time of 1.5 seconds to determine the rate of decay) at different points along a surface and at the boundary conditions of the sound producing and sound receiving zone within the volume to map where the productive and non-productive surfaces were located - where productive surfaces would aid in the creation of stereophonic sound and non-productive surfaces had the perception of echo.

For the fabrication portion of this project we started by brainstorming three different ways that the thermoforming process could be manipulated to allow for economical variation. Three different panel mock-ups would be made to demonstrate how our manufacturing process could effectively create variable geometries.


Figure 1 - Images of HGA performing arts projects (courtesy of HGA) from left to right, top to bottom Valley Performing Arts Center Benedicta Arts Center O’Shaugnessy Auditorium Janet Wallace Fine Arts Center Ordway Center for the Performing Arts (focus of case study) Northrop Auditorium (focus of case study) Illinois State University Performing Arts Center Gallagher Bluedorn Performing Arts Center

Case Study Performing arts centers are an important business sector to HGA. They have a broad range of project experience that span the past 3 decades (Figure 1). The way they interact with acoustical consults varies greatly from project to project. Northrop Auditorium and the Ordway Performing Arts Center were studied because they were ongoing projects and could potentially allow for more candid collection of information. These two projects also represented very different methods of working from the acoustical consultants perspective ranging from highly qualitative to quantitative. Their scale (Figures 2 - 5) and programming are comparable as well; from 1,100 for Ordway to 2,700 for Northrop. Also, the acoustical programming, because it was primarily unamplified sound, dictated similar acoustical metrics for room reverberation rate (a value that is primarily determined by interior volume and percentage of absorptive surfaces). Conversations with acoustical consultants identified that there were three primary strategies for designing with acoustics.1 These strategies were diffusion, transparency, and absorption. A series of diagrams were made that characterized the different surfaces in Northrop and Ordway with respect to these three types (Figures 6 - 11). What emerged through that study was diffusion as the primary strategy for designing with sound in these two performing arts projects (Figures 12 - 13).

1 - It was interesting to hear someone talk about acoustics in terms that I personally usually associate with light. It was a bit of an eye opener in terms of how little I think about acoustic phenomena in architectural spaces.

There were two areas where formal variation was creating an ideal acoustic performance (the balcony fronts at Northrop and the sidewalls of Ordway). The process that the acoustical consultant communicated the criteria for the variation was documented (Figures 14 - 15) to see how both parties could collaborate in the future to design acoustically performative surfaces.


Figure 2 - Plan drawing of Northrop Auditorium with overall room dimensions and other typical performance hall dimensions (seats within 100’ threshold).

Figure 3 - Plan drawing of the Ordway Performing Arts Center with overall room dimensions and other typical performance hall dimensions (seats within 100’ threshold).


Figure 4 - Section perspective drawing of Northrop Auditorium with overall room dimensions and other typical performance hall dimensions (seats within 100’ threshold).

Figure 5 - Section perspective drawing of the Ordway Performing Arts Center with overall room dimensions and other typical performance hall dimensions (seats within 100’ threshold).


Figure 6 - Section perspective showing the locations of acoustically diffusive surfaces in the Ordway Performing Arts Center A1 - Roof structure and catwalks A2 - Angled diffusers A3 - Operable ceiling diffuser A4 - Sidewall panels A5 - Balcony fronts A6 - Under-balcony shaping



A3 A4




Figure 7 - Section perspective showing the locations of acoustically transparent surfaces in the Ordway Performing Arts Center B1 - Wood slats ceiling cladding B2 - Wood slat stage cladding




Figure 8 - Section perspective showing the locations of acoustically absorptive surfaces in the Ordway Performing Arts Center


Figure 9 - Section perspective showing the locations of acoustically diffusive surfaces in Northrop Auditorium A1 - Ceiling Coffers A2 - Back Panel A3 - Balcony Fronts A4 - Sidewalls A5 - Low sidewalls A6 - Stage seating fronts A7 - Proscenium arch reflector



A2 A3 A4

A5 A6


Figure 10 - Section perspective showing the locations of acoustically transparent surfaces in Northrop Auditorium B1 - Proscenium arch



Figure 11 - Section perspective showing the locations of acoustically absorptive surfaces in Northrop Auditorium C1 - Operable curtains



Figure 12 - Section perspective of Northrop Auditorium showing the fixed architectural elements that are acoustically absorptive in red and acoustically diffusive in blue

Figure 13 - Section perspective of the Ordway Performing Arts Center showing the fixed architectural elements that are acoustically absorptive in red and acoustically diffusive in blue


Figures 14,15 - Process diagram showing the different flows of acoustical data for the design of the sidewall panels and balcony fronts of the Ordway Performing Arts Center and Northrop Auditorium

Concept Design

Design Development

Panel Geometry

Architectural concepts



Rules of thumb for surface design

Qualitaive Evalutation

Acoustic Simulation

Concept Design

Design Development


Architectural concepts

Optimized Surface Geometry

Design Sessions W/Real Time Acoustic Feedback


Figure 16 - Process diagram showing a proposed modifying workflow that would center around a shared collaborative acoustical and architectural model

Concept Design

Qualitative Assessment

Shared Model

Shared Model

BEM Analysis



Architectural Concepts

Design Development

Physical Testing Fabrication Process

Sidewall Panel Study The process of designing an acoustical diffusing sidewall panel began with finding out what sort of design criteria we would need to design the surface for and what were important the acoustical and geometric parameters that would be the primary drivers for that process. Our acoustical experts were consulted, and we circled back to the available acoustical analysis tools to evaluate what we could do to improve the body of knowledge that explains how to architecturally manipulate sound quality.


Figure 17 - Outputs and modeling interfaces for the most popular acoustical modeling software. Top image from CATT Acoustic, middle image by EASE Acoustic, and bottom image from ODEON,

Figure 18 - Examples of designer developed plugins that provide acoustic feedback. Top image from Pachyderm for Rhino, middle image from in house tools developed by ARUP, and bottom image from LMN Tech Studio.


Figure 19 - Geometric acoustical analysis of Northrop Auditorium showing the reflected sound and also duration of those sound waves (image by ARUP).

Fabricator Research Our investigation into producing a panel mock-up started by interviewing the fabricator involved in the production of the acoustical sidewall panels for Northrop and Ordway to get a better understanding of the process of creating GFRG panels. We were struck by how low-tech and unsophisticated the process was; plywood pieces were cut out with circular saws and inserts were placed in the mold when a slightly different geometry was preferred. Our eventual panel recommendation called for a situation where every panel would need to have a different mold, which would be extremely expensive. So we expanded our search to include other fabricators where digital processes are more integrated into their current workflow. Initial conversations were had with three listed fabricators (Kreysler & Associates, StructureCraft and RadiusTrack), but the time frame of the project necessitated that we utilize the Digital Fabrication Lab at the University of Minnesota.


Figure 20 - Acoustical panel fabricator research from top to bottom; Stromber, Formglas and Plasterform (Images courtesy of named companies)

Figure 21 - Fabricators with digital fabrication as a part of their process from top to bottom; StructureCraft, Kreysler and Associates and RadiusTrack (images courtesy of named companies)


Figures 22-24 - Variable molding strategies from top. Wood slats with different lengths, piston and scored plastic, and the use of positive and negative air pressure.

Figures 25-27 - Potential output of variable mold strategy to the left.


Figures 28 - Parametric study setup with sources and receivers placed at the edge of the sound production and receiving zones.

Sound Sources



Figures 29 - Direct distance between sound source and receiver


Figures 30 - Reflected distance between sidewall and source and receiver


Figures 31 - Reverberation chart with gradient map applied

dB echo



Parametric Study and Panel Prototype After our working session with Joshua Cushner of ARUP we focused the parameters of our study on reflected sound and direct sound time and on wall articulation depth. The tool we’ve developed could potentially be used to identify trouble spots (areas that produce sound reflections that are perceived as echo) where a deeper and more spherical surface geometry could be placed that would disperse the reflected sound over a bigger area and limit the perception of echo. At the same time that the room tool was being developed, the panel unit and fabrication process was being refined so that we could produce a panel that would be able to flex in depth from 3 to 12 inches and could also produce facets and curves. The strategy that was chosen to develop further used the cnc router to define where facets would occur in the thickened plastic sheet when it was exposed to heat. There was also the option in the parametric definition to route a portion of the plastic to also produce a curved portion where diffusion was preferred over reflection. A half scale prototype was developed with the intention that it would be used to cast a concrete panel to demonstrate that this process could either incorporate the plastic as the finish material or as the formwork for a cast object if a different architectural aesthetic was desired.


Figures 32 - Reverberation map applied to sidewall at all corner points of sound source and sound receiving zones


Figure 33 - Compiled acoustic map used to identify space along the sidewall that provide useful and non-useful sound


Figures 34-36 - Modified variable molding strategy. Form directly derived from previous acoustic map diagram.

Seed the panel with points at random locations. (The number determined by the acoustical map) Number of ‘seed’ points determined by rgb value of acoustic map

Divide the panel using a voronoi subdivision. These lines become engraving paths. Voronoi created from seed points, becomes cnc paths

Route out the internal area where curved geometry is desired. Interior zones routed out to provide curved surface where acoustically desirable

Figures 37 - Expected panel geometry


Figures 38 - Acoustic panel form rules applied to entire sidewall


Figures 39 - Drape molding process

Figures 40 - [failed] casting test


Conclusions One of the most useful things about how this project played out was the fluid definition of the scope that was able to flex as our understanding of the topic and its constraints grew. My personal understanding of the topic was greatly enhanced by this process, and my hope is that everyone involved from HGA and the UMN benefited from it as well. The biggest failing of the project occurred during the prototyping process. There wasn’t enough time from when the parametric tool was developed to fine tune the process enough to control the physical panel with the same amount of control that the digital tool could. There was also an intention from the beginning of the project to use HGA’s connections with fabricators and have them produce the mock-up. Thus fully demonstrating that our process could be implemented at a building scale. Upon the end of the time frame it was suggested that a more appropriate scope for a semester long research project might only include the parametric study. I would also say that if there is an intention to work with fabricators, it is important to get buy in from an interested party very early on in the process. One thing that has come from this process (for me personally) is how the lessons that can be learned from a parametric form-finding research project can be applied to chronic problems that exist in the AEC industry. As our understanding of the world becomes deeper, being able to work with the experts that have the specialized knowledge effectively will allow us to fully take advantage of the technology around us.


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Rindel, J, “Modeling in Auditorium Acoustics – From Ripple Tank and Scale Models to Computer Simulations”, (paper presented at Forum Acusticum, Sevilla, Spain, September 16-20) 2002 Sheil, Bob, “Manufacturing Bespoke Architecture” Nexus Network Journal Issue 14 Vol. 03 (2012): 441-456 Swackhamer, M, Satterfield, B, “Breaking the Mold: Variable Vacuum Forming”, (paper presented at ACADIA Conference, Cambridge, Contario, October 24-27) 2013 van der Harten, A, “Customized Room Acoustics Simulations Using Scripting Interfaces”(paper presented at the 161st Meeting of the Acoustical Society of America, Seattle, Washington, May 23-27 2011) Vrachliotis, G, “Flusser’s Leap: Simulation and Technical Thought in Architecture,” in Simulation: Presentation Technique and Cognitive Method, ed. Gleiniger, A and Vrachliotis, G (Basel: Birkhauser, 2008)


Tuned Surfaces  
Tuned Surfaces  

This research was undertaken as a joint venture between the University of Minnesota’s School of Architecture and HGA as a pilot research in...