AV Acoustics: Collective Wisdom

Four experts, including Acoustical Design Collaborative's Neil Thompson Shade, offer their advice on working in four different environments. 7/27/2009 7:57 AM Eastern

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."

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AV Acoustics: Collective Wisdom

Four experts, including Acoustical Design Collaborative's Neil Thompson Shade, offer their advice on working in four different environments.

Houses of Worship: The New Multipurpose Room

"Optimal acoustics are very denominational-specific in the house of worship market," says Neil Thompson Shade, president and principal consultant for the Acoustical Design Collaborative. During his nearly three-decade career, Shade has consulted on over 800 projects, including over 150 worship houses–Quaker meeting houses, Orthodox Jewish Temples, and every type of Judeo-Christian church.

Christian worship houses, in particular, often present two extremes in terms of sanctuary acoustics. They can be used for both contemporary and traditional, liturgical worship in the same space.

Contemporary worship generally employs a praise band, amplified sound, and large video systems to show lyrics or scripture to the congregation. "The service puts an emphasis on speech intelligibility so the environment is relatively nonreverberant," explains Shade. "Many contemporary worship spaces are large, seating 1,000-plus, and you are designing for a multimedia type of event, which can result in budgets of $1.0 million to $1.5 million for audiovisual systems and acoustical treatment.

"These spaces also have relatively lightweight building construction, similar to big box stores," he continues. "Therefore, mechanical systems and HVAC noise control become paramount because rooftop air handlers result in high levels of noise transmission. A solution is to move the units to grade level."

Contemporary worship spaces tend to use balconies to improve sight lines and to bring congregants closer to the stage, and that in itself can present issues. "The underbalcony can have a different acoustical environment than the floor seating," Shade says. "A solution is to use synthesized reverberation systems to improve the natural acoustical environment under the balcony. These systems can cost $50,000 to $100,000."

In traditional worship spaces, the emphasis is on liturgical music, with the worship space sometimes used for chamber music performances, organ recitals, or choral concerts. "The use can be split evenly between words and music," Shade says. "The challenge is that during a service there are sound sources from multiple locations in the space–from the choir, pastor, congregation participation, organ, and processionals. There is no fixed point of sound origination."

Traditional liturgical music sounds best in a more reverberant environment, but as in all AV projects, it's important to understand your audience: These days, the age group that attends traditional services is getting older. "These services need voice-reinforcement systems to maintain speech intelligibility. Loudspeaker selection and placement is a challenge since ornate architecture makes it difficult to blend in," he says. "Repositioning sound sources like the choir, organ, and reading stations so that a direct line-of-sight is maintained to the congregation can enhance direct sound propagation from these sources to the listener."

AV Acoustics: Collective Wisdom

Four experts, including Acoustical Design Collaborative's Neil Thompson Shade, offer their advice on working in four different environments.

Conference Rooms: Hostile Environments

You know the old saw: size matters. When it comes to conference room acoustics, you can believe it. That's because perhaps the biggest challenge in optimizing conference room acoustics is the variation in size, shape, and usage patterns AV pros must deal with. Some conference rooms are designed to hold fewer than five people, while others are large enough to qualify as an auditorium.

According to the National Fire Protection Association (NFPA), conference room space is calculated using 15 net square feet per person, assuming that the conference room will be furnished with tables and chairs. Timothy W. Cape, founder and principal consultant for Technitect LLC and a Pro AV editorial adviser, believes the average conference room holds 10 to 20 people, which would make the average size from 150 to 300 square feet.

In Cape's experience, conference rooms are seen as shared resources that need to be located near the greatest number of people. Unfortunately, rest rooms and mechanical rooms are also shared resources. "It is inevitable that a conference room is located next to, above, or below a noise source," he says.

Standard issues for conference rooms include background noise, reverberation time, and sound isolation. Noise control of HVAC or building systems is another major concern. Cape says that the standard recommendation for Room Criteria (RC), an update to the older Noise Criteria (NC) rating, is 30 to 35, but you should consider RC 25 to 30 if the room will employ conferencing technology.

If noise is invading the conference room from an outside source–like mechanical equipment on the rooftop, an adjacent fan room, or the health club tenant upstairs–the wall's insulation can be upgraded or more gypsum board can be added for extra isolation. "However, vibration control should be at the source of the noise so it doesn't get into the structure in the first place," Cape says.

Another source of background noise is often found in the room itself, via terminal control devices in the ceiling. "Hallways are usually used as utility pathways. In buildings with tight corridors, terminal control devices are branched off with the ductwork and end up in the room it is serving," Cape says. "The best way to get rid of the noise is to relocate the devices–or the room."

Ductwork can also transmit noise from far away fans. Lining the duct with acoustical material dampens noise, resulting in less noise at the diffuser or grille. "High air flow at the diffusers can be another source of noise," adds Cape. "Upgrading to larger ducts and diffusers reduces air velocity and noise. Diffusers are NC rated but with an assumed set of parameters and only based on one diffuser in a space. If the room has more than one, then the NC ratings must be added together."

As for electroacoustical solutions, Cape says that gating or suppression systems and noise reduction algorithms in conferencing systems are effective. "But you still need to address the room's physical properties," he adds. "The solutions are the same either in a new construction project or an existing space. Either way, sometimes just relocating the room is the cheapest and easiest fix."

(For more from Cape about conference room design, read his ASBPE award-winning piece "A Perfect Blend," at

AV Acoustics: Collective Wisdom

Four experts, including Acoustical Design Collaborative's Neil Thompson Shade, offer their advice on working in four different environments.

Stadiums and Arenas: One Ain't Like the Other

In Oriole Park at Camden Yards, high frequencies (yellow) come from three speakers, while low frequencies (red) come only from the large, front, forward-firing speaker (projection patterns are approximate).

In Oriole Park at Camden Yards, high frequencies (yellow) come from three speakers, while low frequencies (red) come only from the large, front, forward-firing speaker (projection patterns are approximate).

Credit: Courtesy EAW, SIA Acoustics

Modern sports facilities generally come in two flavors: outdoor stadiums and indoor arenas. It seems that everybody–pro sports teams, colleges, municipalities–wants either a new or better one. While they're both challenging to design, they're also very different.

"Arenas tend to have an abundance of mid/low reverberation and plenty of large curved surfaces that create reflections," says Sam Berkow, Pro AV columnist and founding partner of SIA Acoustics, which recently handled the sound updates to Oriole Park at Camden Yards. "In stadiums, the overall reverberation time is low but you have pockets of poor sound environments. Sound system coverage is always the biggest problem, whether it's overlap zones or not enough coverage." However, trying to get stadium owners to integrate acoustical treatment on large surfaces is hard. "It's tricky because sound-absorptive material tends not to survive in high traffic areas," Berkow says. "And covering a large surface area increases the costs dramatically."

One technique that Berkow uses to add absorptive material to an indoor arena is to festoon mid-density fiberglass banners in a shallow U-shape on 60 to 80 percent of the arena's ceiling. This technique can also be used in stadiums with domed ceilings, but the downside is the expense for covering a large area.

Glass balcony railings and corporate suite windows are popular in indoor arenas, but they also create acoustical problems. "We try to slant the glass up and away from the seating area, or we minimize the energy going towards it by not aiming a loudspeaker there," says Berkow.

In outdoor stadiums, the SIA Acoustics team will work with the architect from day one to try and create underbalcony spaces with a tall ceiling and advantageous angle to direct sound. "A tip is to angle some of the underbalcony surfaces or create surfaces that scatter sound. As a result, you end up with less reflection," Berkow says.

For existing balconies, he observes, "It is harder and harder to get retrofit space on an overhang because dimensions are so tight. You could use the space on the front of balconies, but they are dominated by signage. Another alternative is to work with the signage people to create microperforated signs with acoustical batting behind them."

For both types of venues, it's important to control off-axis energy from loudspeakers. When it comes to outdoor field seating in particular, the trick is to roll off the low frequency at the underbalcony loudspeakers but pair them with a full-range loudspeaker firing in the opposite direction.

"The idea is to limit the bandwidth of the speaker in the underbalcony space to control coverage. Single speakers often become omnidirectional below 250 Hz and now that energy is bouncing all over the concrete, which takes away from articulation," Berkow says.

He warns that ultradistributed systems, in which architects or owners try to hide extra-small loudspeakers in signage or railings to bring direct sound closer to the seats, are gimmicky. "You pay more for packaging than performance," he says. "There is always another alternative to improve the listening experience. The key is to EQ the speaker so that the interaction with the room is optimal. The computer is there to quantify the interaction and response, but critical listening is always part of the process."

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