TM 5-805-4/AFJMAN 32-1090
CHAPTER 4
SOUND ISOLATION BETWEEN ROOMS
4-1. Objective.
section 4-3. There are many other references that
provide transmission loss performance for building
This chapter provides data and procedures for
materials. In addition many manufactures also
estimating the changes in sound levels as one
provide transmission loss for their products.
follows the "energy flow" path from a sound
(1) "Suggested" vs "ideal" TL values. In sev-
source to a receiver, through building components,
eral of the tables of sections 4-3 and 4-4, two sets
such as walls, floors, doors etc. First, the sound
of TL data are given. The first is labeled "sug-
pressure levels in the room containing the source
gested design values," and the second is headed
drop off as one moves away from the source as
"ideal values." With good design and workman-
described in chapter 3. Then, at the walls of the
ship, the "suggested design values" can be ex-
room, some sound is absorbed, some is reflected
pected. The "ideal values" are perhaps the highest
back into the room, and some is transmitted by
values that can be achieved if every effort, in both
the walls into the adjoining rooms (this also occurs
design and execution, is made to assure a good
at the floor and ceiling surfaces). The combined
installation, including control of all possible flank-
effects of this absorption, reflection, and transmis-
sion are the subject of this chapter.
ing paths of sound and vibration. The "suggested
design values" are 1 to 3 dB low the "ideal
4-2. Sound Transmission Loss (TL), Noise Re-
values" in the low-frequency region and as much
duction (NR) And Sound Transmission Class
as 10 to 15 dB lower in the high-frequency region.
(STC).
When walls have ideal TL values as high as 60 to
With the knowledge of the acoustical isolation
70 dB, even the slightest leakage or flanking can
provided by walls and floors, it is possible to select
seriously reduce the TL in the high-frequency
materials and designs to limit noise intrusion from
region.
(2) TL of other materials and fabricated parti-
adjacent mechanical equipment rooms to accept-
able levels. The degree of sound that is transmit-
tions. Because of the increasing need for good
ted is influenced by the noise isolation properties
sound isolation in building design, many manufac-
of the demising construction, the area of the
turers are producing modular wall panels, movable
demising wall, floor or ceiling and the acoustical
partitions, folding curtains, and other forms of
properties in the quiet room.
acoustic separators. When inquiring about these
a. Transmission loss (TL) of walls. The TL of a
products, it is desirable to request their transmis-
wall is the ratio, expressed in decibels, of the
sion loss data and to determine the testing facility
sound intensity transmitted through the wall to
where the product was evaluated (i.e. laboratory vs
the airborne sound intensity incident upon the
field, and the standard employed).
(3) Estimated TL of untested partitions. For
wall. Thus, the TL of a wall is a performance
characteristic that is entirely a function of the
estimations of the TL of an untested partition, its
average surface weight (in lb./ft.2) and its basic
wall weight, material and construction, and its
numerical value is not influenced by the acoustic
structural form should be determined. Then, the
environment on either side of the wall or the area
range of approximate TL values for partitions of
similar weight and structure should be obtained.
of the wall. Procedures for determining transmis-
b. "Noise reduction" (NR) of a wall. When sound
sion loss in the laboratory are given in ASTM E
90. This is the data usually given in most manu-
is transmitted from one room (the "source room")
facturers literature and in acoustic handbooks. Lab-
to an adjoining room (the "receiving room"), it is
the transmitted sound power that is of interest.
oratory ratings are rarely achieved in field instal-
lations. Transmission loss values in the laboratory
The transmission loss of a wall is a performance
are usually greater, by 4 to 5 dB, than that which
characteristic of the wall structure, but the total
sound power transmitted by the wall is also a
can be realized in the field even when good
function of its area (e.g. the larger the area, the
construction practices are observed. ASTM E 336
more the transmitted sound power). The Room
is a corresponding standard method for determina-
Constant of the receiving room also influences the
tion of sound isolation in buildings (in situ). The
SPL in the receiving room. A large Room Constant
approximate transmission loss or "TL" values,
reduces the reverberant sound level in the room at
expressed in dB, of a number of typical wall
an appropriate distance from the wall. Thus, three
construction materials are given in the tables of
4-1
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