TM 5-805-4/AFJMAN 32-1090
d. Windows. Fixed windows will be close to
characteristics because the wood stud conducts
vibration from one side to the other. This can be
their laboratory TL rating. Operable sash windows
easily remedied by using a metal resilient channel
can be 10 dB less than the lab rating due to sound
which is inserted between the wood stud and
leaks at the window frame. Gaskets are necessary
drywall on one side. Nonload-bearing metal studs
for a proper seal. Some window units will have
are sufficiently resilient and do not improve with a
unit TL ratings which would be a rating of both
resilient channel. Load-bearing metal studs are
the gasketing and glass type. Double-glazed units
stiff and can be improved with resilient channels
are no better than single-glazed if the air space is
installed on one side.
1/2 inch or thinner. A 2-inch airspace between
(2) Fibrous blankets. Fibrous blankets in the stud
glass panes will provide better noise reduction.
cavity can substantially improve a wall's perfor-
Laminated glass has superior noise reduction capa-
mance by as much as 10 dB in the mid and high
bilities. Installing glass in a neoprene "U" chan-
frequency range where nonload-bearing metal
nel and installing sound absorbing material on the
studs, or studs with resilient channels, are used. A
jamb between the panes will also improve noise
minimum 2 inch thick, 3/4 lb/ft3 fibrous blanket
reduction. Special acoustical window units are
should be used. Blankets up to 6 inches thick
available for critical installations.
e. Transmission loss values for building parti-
provide a modest additional improvement.
(3) Double or staggered stud walls. When a high
tions. Tables 4-2 through 4-11 provide octave
degree of noise reduction is needed, such as be-
band transmission losses for various constructions,
comments or details on each structure are given in
tween a conference room and mechanical room,
the footnotes of the tables. STC ratings are useful
use double or staggered stud wall construction
for cursory analysis when speech transmission is
with two rows of metal or wood studs without
of concern. The octave band transmission losses
bracing them together, two layers of drywall on
should be used a more thorough analysis, particu-
both sides, and a 6 inch thick fibrous blanket.
larly when the concern is for mechanical equip-
b. Masonry walls. Masonry construction is
ment.
heavy, durable, and can provide particularly good
low frequency noise reduction. Concrete masonry
Table Construction Material
units (CMU) made of shale or cinder have good
No.
noise reduction properties when they are approxi-
4-2
Dense poured concrete or solid-core concrete
mately 50 percent hollow and not less than me-
block or masonry.
dium weight aggregate. Parging or furring with
4 - 3 Hollow-core dense concrete block.
drywall on at least one side substantially improves
"Cinder block" or other lightweight porous
4-4
the noise reduction at higher frequencies. The
block with sealed skin.
thicker the block, the better the noise reduction.
4-5 Dense plaster.
An 8 inch thick, semi-hollow medium aggregate
4-6 Stud-type partitions.
4 - 7 Plywood, lumber, wood doors.
block wall with furring and drywall on one side is
excellent around machine rooms, trash chutes, and
4-8
Glass walls or windows.
elevator shafts.
4-9 Double-glass windows.
c. Doors. The sound transmission loss of both
4-10 Filled metal panel partition and acoustic
hollow and solid core doors will substantially
doors.
4-11 Sheet aluminum, steel, lead, and lead-vinyl
increase when properly gasketed. Regular thermal
curtain.
type tape-on gaskets may not seal well because of
door warpage, and can also cause difficulty in
4-4. Transmission Loss Of Floor-Ceiling Combi-
closing the door. Tube type seals fitted into an
nations.
aluminum extrusion can be installed on the door
Many mechanical equipment areas are located
stop and fitted to the door shape. Screw type
immediately above or below occupied floors of
adjustable tube seals are available for critical
buildings. Airborne noise and structureborne vi-
installations. Sills with a half moon seal at the
bration radiated as noise may intrude into these
bottom of the door are recommended in place of
occupied floors if adequate controls are not in-
drop seals, which generally do not seal well. Two
cluded in the building design. The approximate
gasketed doors with a vestibule are recommended
octave band "TL" and "NR" are given here for
for high noise isolation. Special acoustical doors
five floor-ceiling combinations frequently used to
with their own jambs and door seals are available
control airborne machinery noise to spaces above
when a vestibule is not practical or very high
and below the mechanical equipment room. To
noise isolation is required.
4-6
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