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 proavmagazine.com/perfectblend.)