Design Guide: Band Training Facilities
DG-1110-3-119
Practical Approaches for Accoustic Construction
March 1983
tains affords acoustical variability.
Typical NRC's of various finishes and treatments are given
in Table 5-4. Specific materials suitable for music prac-
A wide variety of acoustical ceilings, made of mineral
q
tice and rehearsal rooms are described below.
fiber, fiberglass, as well as fiber-backed perforated
metal. These should always be suspended at least a
q Semi-rigid fiberglass board, 1" to 2" thick, covered
foot below the solid deck or ceiling, to enhance low-
by a sound-transparent material such as cloth, perfora-
frequency absorptivity.
ted vinyl or metal, or an open mesh or screen.
q A similar detail to the above, made of fiberglass batts,
The basic guidelines regarding placement of absorptive
or if a dark finish is desired, of fiberglass duct liner
materials are: (1) always treat the ceiling, most usually
board. (Batts are also very effective if placed behind
with suspended acoustic tile; (2) always treat at least
fiberglass board, to increase the treatment's thickness
the equivalent of one wall, but preferably spread the treat-
to 3" or 4".)
ment over several walls; (3) if any two walls are parallel,
treat one or both so that no major opposite and parallel sur-
*The Noise Reduction Coefficient (NRC) is the arithmetic
faces remain hard. In general, this will assure a sufficient
average of a material's sound absorption coefficients in the
quantity of absorptive material (for loudness and reverbera-
octave bands centered at 250, 500, 1000 and 2000 Hertz,
tion control), a fair state of diffusion in that the absorb-
rounded off to the nearest multiple of 0.05.
ers are distributed throughout the room, and adequate flutter
q Wood-fiber panels such as "Tectum", backed by at
control.
least 1-1/2" batts, since such panels alone are not
very efficient.
Floors may be carpeted, but do not need to be. As indi-
q Heavy--typically velour-curtains, draped to one-half
cated in Table 5-4, carpet is a poor absorber. Adding it
to the other, required absorbers (on the walls and ceiling)
to two-thirds their flat area, and heId 6" or more off
will afford little additional control.
the wall. As noted earlier, the movability of such cur-
Table 5-4 Approximate Acoustical Absorptivity of Room Finishes and Treatments
NRC*
Floor Finishes:
0.05
All hard and rigid finishes
0.10
Wood on joists
0.25
Average glue-down carpet
0.35
Thick carpet without underpad
0.45
Thick carpet with underpad
Wall Finishes:
0.05
Brick, drywall, etc.
0.10
Painted concrete block
0.25
Unpainted concrete block
0.45
Medium-weight curtains
0.50
Tectum or similar (average)
0.60
Heavy curtains
0.60
Mineral fiber wall panels
0.75
Glass fiber wall panels (1")
0.80
Tectum over glass fiber
0.90
Glass fiber wall panels (2")
Ceiling Finishes:
0.05
Concrete, steel deck, etc.
0.05
Suspended plaster or drywall
0.10
Wood boarding
0.50
Mineral fiber tile - minimum
0.65
Fibrous spray (1", well applied)
0.65
Acoustical deck systems (average)
0.80
Mineral fiber tile - maximum
0.85
Well-perforated metal pan with insulation
0.90
Glass fiber ceiling board
*Higher number indicates better performance. See 5-4.A for definition of NRC.
5-23
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