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Sound Control In Gymnasiums

Gymnasium / Multipurpose Room Acoustics Sound Control in Gymnasiums
by Nick Colleran

Originally Published in Christian School Products magazine March 2011.

Material: Absorbers, Diffusers

Sonora® Wall Panels, Cloudscape® Baffles, Gymnasium, Fitness & Multipurpose

Gymnasiums and indoor swimming pools have two things in common: lots of hard reflective surfaces and a resulting lack of speech intelligibility. The first thought for sound control is usually acoustical wall panels, which absorb sound but also water and therefore, have one strike against them for the pool area. In this case, acoustical baffles are usually the best choice for sound absorption without moisture absorption. They are also the best place to begin treatment for a gymnasium

Initially, it seems counterintuitive not to treat the wall first, after all, isn’t the sound bouncing off the walls and around the room? True, but the typical gym may have a reverberation time of between three to seven seconds. While an echo is a discrete reflection, reverberation is a series of non-directional, indistinguishable reflections. The sound appears to be everywhere. The best means of reducing long reverberation times is to add the most exposed, acoustically absorptive material into the space. Hanging baffles, with two sides exposed to the sound as well as edges, have that.

A 2’ X 4’ hanging baffle has twice the surface area of a wall panel of the same size plus the edge area which may not be exposed if wall panels are mounted contiguously. A 2-inch baffle has 18 square feet of absorptive area with a coefficient approaching the theoretical limit of 1.00. A wall panel would be limited to its front surface of eight square feet with the same coefficient. Care should be taken when using these numbers in various computer programs, to enter the total exposed area of the baffle rather than just the front surface. To do otherwise will yield impossible coefficients and result in exceptionally “dry” rooms, if the program limits absorption to 1.00.

The next stage is to control side-to-side reflections by adding wall panels where a direct reflection produces an annoying echo. Since reverberation is being brought down by the hanging baffles, and there is seating to break-up the reflections (scattering and diffusion), fewer are needed. However, it is recommended that they be high-impact to avoid damage from a direct hit by basketballs, if the gym is active. The vinyl covered ceiling baffles will dodge and “duck” out of the way, if an object travels high enough to reach them.

To paraphrase a line from a classic movie song: “A gym is still a gym.” It should sound still like one, just better. Compromise of the ideal reverb time for each intended function will allow the broadest use of the facility. A modern sound engineer (and for that matter the speaker) may prefer a very dry room for intelligibility with electronics used to add-back ambience when needed. An overly “dead” sounding gym will create a sonic disconnect with the visual space, somewhat disorienting, like a studio recording “dubbed-in” to a live, outdoor sound track, without matching ambience to surroundings.

In summary, baffles are the lowest cost, most efficient and least intrusive means to tame large room reverb. Being out-of-sight requires less dollars out-of-wallet for finish, since they are often above the lights and unnoticed. Extra surface area requires fewer pieces to perform the task and wall panels can then polish the result and provide visual interest.

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