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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. |
