Virtual but Vivid

A sonic rendering technique known as auralization helps acousticians make the sound of even unrealized spaces audible.
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Joann Gonchar, AIA

After completing its survey, Acentech digitally modeled Safdie's court and virtually "populated" the space with various scenarios, including the sounds made by 500 diners at a banquet, with people conversing and dishes clinking. Since it was impractical to make a recording of such a source in an anechoic chamber, the acousticians recorded a much smaller group in a relatively nonreverberant restaurant. They mathematically adjusted the model to compensate for the recording environment and processed the sounds to simulate a large number of diners occupying tables situated around the room making noise at different volumes.

Long and thin Kroon Hall, at Yale University, is organized around a skylit stair that connects the building's four floors. The configuration, combined with the building's ventilation strategy, posed a potential noise-transfer problem between the central circulation space and flanking offices.

Photos: © Morley von Sternberg (top); Robert Benson (bottom )

1 Mixed-mode ventilation
2 Photovoltaics
3 External shading
4 Displacement ventilation

5 Exposed thermal mass
6 Over-door ventilator
7 Exhaust air

With auralization of Peabody Essex serving as a point of reference, the consultants constructed an acoustic model of the MFA scheme. They studied the information garnered from the model to understand the effect of the proposed geometry and materials. They repeated the auralization process, simulating the sound of the unbuilt space with various sound sources and levels of acoustical treatment.

As a result of this benchmarking, analysis, and simulation process, the museum's trustees and the architects reached a consensus that the room would need an average coefficient of absorption of 0.3 at midrange frequencies and a total absorption of about 16,500 sabins (one sabin represents the amount of absorption provided by one square foot of perfectly absorptive material). The ultimate solution included incorporating most of the required acoustic material in the ceiling as part of elements that also help control heat gain and glare: a central band of perforated V-shaped metal baffles running through the center of the space and into the galleries, with translucent panels made of two layers of microperforated vinyl on either side. Glass fiber concealed within column enclosures (where sophisticated speakers are also hidden) and wood fins on an existing masonry wall provide additional sound absorption.

Tolerable transmission

Though most often used to render room acoustics, auralization can also be deployed in other areas of concern to architectural acousticians, including sound isolation between adjacent spaces. Auralization played such a role at Kroon Hall, a building for the Yale School of Forestry completed on the university's New Haven, Connecticut, campus in the spring of 2009.

Designed by London-based Hopkins and the Connecticut firm Centerbrook, with Arup providing multidisciplinary engineering, the long and thin four-story structure is organized around a slotlike stair that cuts through a narrow, skylit atrium. The LEED Platinum−certified building contains many coordinated, aggressively green features, including a mixed-mode ventilation system that supplies fresh air through a raised-floor ventilation system and, depending on the season, operable windows. The system exhausts return air passively through the central atrium, creating a potential privacy issue, since telephone calls or faculty-student conversations might travel from private offices flanking the atrium through vents positioned over doors.

In response, the architects devised a custom U-vent for the office-door transom. However, the proposed assembly allowed an unacceptable level of sound transfer. As an alternative, Arup suggested an advanced off-the-shelf vent, roughly equal in price to the custom solution. The device still allowed some sound to travel through the partition, but it significantly improved the assembly's sound transmission class, or STC, a rating of how well a building component attenuates airborne sound. An auralization convinced Yale officials that the sound of voices coming from offices would be barely audible to anyone standing nearby.

Auralization can similarly be applied to curtain-wall design, helping designers evaluate an assembly's ability to block the noise of a busy highway or a nearby airport. Or it can be used as an aid for evaluating noise-control options for a particular piece of mechanical equipment. But regardless of the application, practitioners of the technique say that it is a powerful decision-making tool. "To both architects and users, auralization conveys the efficacy of an acoustical strategy," says Markham. "It allows them to understand what we are recommending and why."

 

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Originally published in Architectural Record
Originally published in February 2011

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