DG-1110-3-119
Design Guide: Band Training Facilities
March 1983
Practical Approaches for Accoustic Construction
F. Lighting and Electrical Systems
isolating barriers, they should be well-sealed (to maintain
airtightness) and, if the barrier is resiliently attached, the
Electrical systems must be designed to eliminate noise
box or switch must not compromise the resiliency. Figure
from the fixtures themselves, to prevent components and
5-18 illustrates a light fixture hanger passing through a
conduits from transmitting sound from one room to
resiliently hung ceiling. The caulked joint around the hanger
another, and to avoid air leaks incidental to installation.
rod not only seals the opening but also avoids rigid con-
tact between the resiliently suspended ceiling and the rod.
Ballasts for fluorescent lighting in any music room used
The resilient ceiling hanger is also shown. An escutch-
for critical recordings should be installed remote from the
eon is optional to hide the joint.
room, to eliminate noise. In Individual Practice Rooms,
use A-rated ballasts, which may be located at the fixture.
Any clocks in music rooms should be silent-type.
5-3 Noise Control and
To avoid conduits becoming conductors of sound, slack sec-
tions of flexible conduit should be used where they cross
Mechanical Systems
music room walls which have resilient gypsum wall board
skins. Avoid running power distribution conduits above
Background noise in buildings is primarily produced by out-
music spaces, or across their ceiling plenums. Try to avoid
door traffic and the building's own mechanical systems.
wiring within isolation walls, as the solidity of the construc-
Traffic noise is seldom a problem in closed, air-conditioned
tion will be compromised. Wall outlets should never be back
buildings, unless they are located along busy streets or
to back.
highways, which is not recommended (see 2-5.A.3).
Use of surface mounted fixtures will avoid cutting large holes
The mechanical systems must be engineered for quiet
in isolation walls and ceilings, although lighting may be
operation, but preferably so that the noise level is not much
recessed in the absorbent ceilings that are not part of
below the applicable NC criteria (see Table 3-1). Bland
isolation. (Sound-rated suspended ceilings are designed
background noise, at modest levels, helps mask other intru-
for integral lighting without compromising their performance).
sive sounds, with which even the best sound-isolating
If outlet boxes and switches must be recessed into sound-
barriers cannot cope. The principal sources of this mechani-
cal system background noise are: the fans that circulate
air; the ducts, including volume control boxes, that distrib-
ute the air; and the diffusers and grilles through which
air enters and leaves the room. Each must be considered
if correct background noise levels are to be achieved.
A. Fan Noise. Fan noise--often a low-frequency
rumble--travels equally with and against the airflow.
Consequently, supply and return air systems merit
equal consideration. The initial noise level (at the fan)
depends on factors such as fan type, capacity (cfm),
and static pressure. In general, the larger the fan, the
noisier it is. The noise is carried by the ducts which,
unless treated, offer very little attenuation. The only
acoustically effective treatments are internal glass fiber
lining (not less than 1" thick) and silencers that can be
inserted in the ducts.
B. Duct Noise. Noise generated in the ducts is due
turbulence caused by sudden velocity changes, sharp
turns, and generally by high air speeds. It tends to be strong-
est in the middle frequencies. The best solution is to mini-
mize duct noise by careful design-by promoting smooth
airflow at moderate velocities-and by inserting adequate
lengths of acoustically-lined duct between points of turbu-
lence (such as volume control boxes) and the room.
In general, ducts between fans and the music rooms they
serve should be of generous length and lined with 1"
fiberglass. In addition, if ducts are of insufficient length, manu-
factured duct-silencers should be inserted. Common ducts
serving several music rooms should be long, with some 90
bends, and acoustically lined. In buildings served by high-
-pressure, high-velocity systems, pressure and velocity must
be reduced outside the music rooms, i.e. before ducts
penetrate the rooms' sound-isolating constructions.
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