AV Acoustics: Collective Wisdom
Four experts, including Acoustical Design Collaborative's Neil Thompson Shade, offer their advice on working in four different environments.
It seems to happen more often than not. You walk into a room or venue and the acoustics are so bad they assault your ears. And you wonder if the people in the room, if the client or building owner, even realizes they're missing half of what they should be hearing. Or that with a little extra help from an AV expert, they could be getting from their AV systems exactly what they paid for–or more.
Neil Thompson Shade, president of the Acoustical Design Collaborative, at the Immaculate Conception Catholic Church in Towson, Md.
Credit: Johnathan Hanson/Aurora Select
Acoustics is one of those topics in pro AV that can start a lively discussion or a tense argument, depending on the parties involved. Acousticians bear the responsibility to right acoustical wrongs in a particular space, whether those wrongs are the result of inattentiveness, error, or just plain physics. Optimal acoustics are especially important in places like classrooms, houses of worship, conference rooms, and stadiums and arenas, where people count on intelligibility. No matter what your role is in designing AV systems–integrator, designer, consultant–it's important to keep in mind the acoustics of the location where you're working.
We asked four experts for their advice on optimizing acoustics in four distinct AV spaces. This is what they said.
Classrooms: For the Sake of Comprehension
Anyone who's gone to school in the past three decades can visualize the typical classroom: drop tile ceiling, thin carpet or tile floor, and a row of windows. Modern classrooms may also have a bank of computers, as well as AV equipment like a projector, document camera, or sound system.
"The problem is the old models of design don't always fit the current styles of teaching," says Daniel C. Bruck, LEED AP and president of BRC Acoustics & Technology Consulting. "And new styles of classroom design with sloped ceilings and larger volume or more windows to increase natural light can also increase reverberation time."
Bruck is intimate with the topic. He's the committee chair for the U.S. Green Building Council committee on acoustics in classrooms and a member of the working group that developed the ANSI S12.60 Acoustical Performance Criteria, Design Requirements and Guidelines for Schools (see Consultant's Connection, page 14).
Typical acoustic problems in classrooms can be caused by a long reverberation time and noise intrusion, such as from mechanical systems. "Poor acoustics is usually the result of inattention by the design team," Bruck says. "By that I mean the team didn't think of incompatible adjacencies and placement of mechanical systems early in the process. Also, value engineering often takes out things like acoustical treatments or silencers on HVAC systems."
Common classroom design situates students near noisy mechanical equipment, reducing speech intelligibility and learning comprehension. This equipment can include unit ventilators, closet heat pumps, and others. "Even computer workstation fans can be loud and, depending on seating, can be directly behind the adjacent student's seat location," says Bruck. "Projector fan noise can provide a built-in noise floor that is hard to overcome as well."
Bruck suggests a recessed ceiling mount or a ventilated projector enclosure to keep fan noise from the students. To mitigate other noise issues, change out ceiling tiles to something more sound absorptive, add carpet or carpet tiles to absorb more sound and reduce noise from moving chairs and footfalls, and keep the windows closed.
Cost is always a concern for schools, and Bruck says that there are always high- and low-cost options for improving a classroom's acoustics. "It depends on the client's objectives; the trade-off is often between looks and performance," he says. "For example, you can choose a spray-on acoustical finish that is inexpensive and performs as needed, but may not meet the architect's requirement for visual appearance. For mechanical systems, a central HVAC system will probably have lower noise, but the additional ductwork may produce added cost."
A recent development in the education market is the use of amplified sound in a classroom. Companies like Listen Technologies and Williams Sound continue to introduce newer, better voice uplifiting systems. But those can be a Band-Aid solution. "My fundamental belief is to control reverberation time and noise control, first and foremost," Bruck says. "Just installing a sound system is not a solution."
The Acoustical Society of America has issued a position paper regarding amplified sound that says "sound amplification should not be routinely employed in typical small mainstream classrooms." However, Bruck points out that "if you have reverberation time under control and mechanical noise less than 35 dBA, then electronic sound enhancement can be okay," he says. "But it needs to be a well-designed system, with good clarity and uniform sound distribution."