Can You Hear Me? Optimizing Learning through Sustainable Acoustic Design

Understanding acoustic design, surface materials and services will provide optimal educational environments.
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Sponsored by Ceilings Plus, Meyer Sound Laboratories, Inc. and Serious Materials
Celeste Allen Novak, AIA, LEED AP

Active acoustic system as part of the design of the Laboral University in Gijon, Spain.

Photo courtesy of Meyer Sound Laboratories, Inc.

The components

To design the room with an active acoustic system, professionals should specify, as a base configuration, a room volume sized for speech intelligibility. This room should have the recommended absorptive materials for low reverberation times even for low frequencies. Active acoustic systems can add reverberation electronically, tuning the sound in the room to meet the additional requirements for hearing music or other types of performances.

They can also increase speech intelligence by providing voice lift and create an "electronic orchestra shell" for listeners as well as for musicians to hear themselves on stage. These systems can be installed to be invisible to the eye, and they can be embedded in perforated walls or ceilings.

Active acoustic systems incorporate the following components:

  • Microphones in the room to pick up direct sound near a performer
  • Microphones in the audience to pick up existing reverberation
  • Loudspeakers that regenerate sound to tune the performance to the required acoustic signal
  • Digital signal processors that contain the communications hardware
  • Services by trained experts who will locate equipment into existing buildings as well as work with the architect in the early stages of design to provide the minimal room design for performances in new facilities.

An active acoustic system added voice lift to make speech sounds intimate and intelligible during a technical seminar at the Pearson Theatre, Meyer Sound Laboratories, Inc, Berkeley, California.

Photo courtesy of Meyer Sound Laboratories, Inc.

Is it green?

According to Roger Schwenke, who is beginning a research study on the possible environmental benefits of active acoustic systems, these systems offer a means to change the acoustics of a room electronically. They are an alternative to physically variable acoustic treatments such as retractable curtains, or doors opening to reverberant chambers. They are green because they provide the alternative to building multiple performance spaces in schools, from K-12 to a university setting. By using active acoustic systems, the cubic volume in a room can be smaller, and therefore the amount of materials needed to construct the building, the energy used in the HVAC and lighting systems are reduced. A lower volume of construction means fewer materials in construction and to transport. Potentially, there is the added benefit of more open space on the site of a shrunken building envelope. Active acoustics can change the sound quality of a room by pushing a button, rather than constructing more square footage.

Zellerbach Hall Acoustic Retrofit

An analysis of this auditorium determined the placement of the components of an effective active acoustic system at Zellerbach Hall, University of California Berkeley.

Image courtesy of Meyer Sound Laboratories, Inc.

The 2,014 seat Zellerbach Hall was designed in 1968 as the permanent home and largest indoor venue of Cal Performances, UC Berkeley's premiere music, dance and drama events space. This building won an AIA award for design excellence and it has been the site for numerous performing arts programs including the home of the Berkeley Symphony Orchestra. It was designed for exceptionally diverse programming in the 1960s when architects Vernon DeMars and Donald Harrison had few options for dealing with the diverse acoustic demands of these performance types. Variable acoustics methods involving physical or mechanical means were expensive and electronic enhancement was in its infancy. The architects opted for the only reliable solution available at the time: a "happy medium" wherein the acoustics were acceptable for most of the hall's programs, if optimum for only some.

The resulting mid-band reverberation time ended up being 1.45 seconds. This was an ideal length for chamber music, opera and recitals, but at the high end of acceptability for dramatic and spoken-word performances. Music benefiting from a longer and more complex reverberation characteristic, such as orchestral and choral performances, and some types of ethnic and electronic music, was, of necessity, more compromised. They employed a traditional orchestra shell, to add projection and increase the ability of the musicians to properly hear one another, but it was labor- and time- consuming to construct and de-construct for each performance.

"We had been grappling with this issue of maximizing the hall's sound for a number of years," says Cal Performances director Robert Cole. "We know the acoustics are quite good as they are; many wonderful artists have performed here with great success. There have been, however, some instances, such as when a period orchestra like Philharmonia Baroque Orchestra performed, when I have wished we could modify the architecture of Zellerbach to better replicate the space in which the music was originally meant to be performed." The challenge presented by Zellerbach Hall was to extend and enrich the venue's excellent physical acoustics while gaining a second acoustical environment similar to that of a classic concert hall.

The auditorium also housed graduations and speakers throughout the years, in spite of the challenging acoustical environment. In 2006, the University was approaching its 100-year anniversary and for its gala celebration, they planned to include a wide array of performers from dance to opera. They met with an active acoustics engineering team and Cal Performances, setting three main acoustic goals. The first was to provide an enhanced level of natural-sounding reverberation throughout the hall when desired for selected types of performances. The second goal was to improve projection of sound into the hall, and to allow musicians onstage to clearly hear each other, when the orchestra shell is not in place - essentially by adding a "virtual orchestra shell" as an alternative to the hall's mechanical one. Lastly, the installation needed to be natural sounding as well as not visually obtrusive in this award-winning building.

The installation was successful in meeting all of its goals and as Cal Performances music director, Robert Cole, said, "we planned our Centennial Gala comprised of dance, music and a large orchestra and chorus all in one evening. Installing the active acoustics retrofit was the only way we could pull it off."1

A broad range of acoustical characteristics can be provided by active acoustic systems and services. This graph of reverberaton time over frequency shows the range of responses available to Zellerbach Hall, from that of the pure physical acoustics to that with the active acoustics system.

Chart courtesy of Meyer Sound Laboratories, Inc.

 

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Originally published in Schools of the 21st Century
Originally published in January 2010

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