TM 5-805-4/AFJMAN 32-1090
CHAPTER 9
MECHANICAL NOISE SPECIFICATIONS
9-1. Objective.
the sound transmission loss (TL) required. The
laboratory procedure is given in ASTM E 90.
Once noise and vibration control has been deter-
ASTM standards E 336 and E 966 provide proce-
mined it is then necessary to specify the perfor-
dures for in-situ evaluations of building partitions
mance and materials for the noise control treat-
and building facades, respectively. For machinery
ments. This chapter covers specifications for
enclosures the interior sound absorptive properties
specialized acoustical products commonly used in
also need to be specified. ASTM standard C 423
building mechanical systems. Manufactures can
and E 795 provides methods for mounting and
also provide guidance for acoustical products. Com-
measuring sound absorptive properties in the labo-
monly used noise control products include mufflers
ratory. ASTM standard E 596 provides a labora-
in ducting systems and vibration isolation prod-
tory method of rating the noise reduction of sound
ucts. In addition a noise level limit may be
isolating enclosures. In addition there are stan-
imposed on the equipment to be used, in which
dards for the installation of partitions which are
case it is the responsibility of the manufacturer to
provide suitable noise or vibration control which
intended to provide sound isolation, such as ASTM
will meet the criteria.
E497.
9-2. General Consideration.
9-4. Mufflers and Duct Lining For Ducted Ven-
tilation Systems.
All noise control specifications should include
some common information. This includes:
The acoustical performance for duct lining and
a. Some statement as to the rationale for the
mufflers is usually specified to be made in accord-
noise control treatment. Although it may not be
ance with ASTM Standard E477. It should be
the responsibility of the supplier to met the overall
noted that this is a laboratory standard and
objective, if they know the overall objective they
includes insertion loss and regenerated noise (for
may be able to provide guidance on the application
mufflers). All suppliers of prefabricated duct muf-
of their product to aid in achieving the overall
flers should be required to submit muffler perfor-
objective.
mance in accordance with this standard. In addi-
b. Materials of construction that will be accept-
tion many suppliers of duct mufflers will also
able. This can be stated specifically or it can be
provide guidance on how actual field installation
given in general terms.
may modify the laboratory performance.
c. Conditions under which the material or items
9-5. Sound Levels For Equipment.
will be used. This mainly pertains to the environ-
mental conditions (e.g. temperature, flow velocity,
Due to the variety of equipment installed in
pressure etc.).
buildings and the multiplicity of uses for each
d. Acoustical performance that is expected. This
equipment item, there are a number of standards
can be the specific performance of a noise control
for measurement of sound from mechanical equip-
item or it can be the overall performance.
ment. There are many ANSI standards that de-
e. How the acoustical performance is to be eval-
scribe general procedures for the measurement of
uated. This is the most important and difficult
sound power levels and sound levels of equipment,
portion of any specification. This may take the
both in the laboratory and in field. ARI has
form of a laboratory test or a test in the field
produced several standards for the measurement of
under actual operating conditions. The references
air-conditioning equipment. The noise level esti-
provide ASTM, ARI and ASHRAE standards com-
mates given in this manual will probably equal or
monly used to evaluate acoustical performance in
exceed the actual noise levels of approximately 80
the laboratory and in the field.
to 90 percent of all those types of machinery that
f. And finally what action is expected in the
will be encountered in typical building use. In
event that the specified performance is not met.
many cases, actual noise levels may fall 3 to 6 dB
below the estimates, and for some types of equip-
9-3. Partitions And Enclosures.
ment some noise levels may fall as much as 10 to
The performance specification of partitions and
15 dB below the estimates. Thus, there appears to
be no shortage of available equipment that will
enclosures usually includes the sound isolation
properties. The most common method is to specify
fall at or below the estimated noise levels given in
9-1
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