TM 5-805-4/AFJMAN 32-1090
procedures and suggestions for specifying noise
the manual, and it would not be discriminatory or
data (SPL or PWL) on any desired piece of equip-
unreasonable to specify that any purchased equip-
ment. This is not offered as a "standard" for noise
ment for a particular building be required not to
measurements, however. Any acceptable and appli-
exceed the estimated values given here for that
equipment. This is especially true if the actual
cable measurement and specification procedure
acoustic design of a wall or floor or room treat-
recommended by an appropriate standards group
ment is dependent upon one or two particularly
(such as ANSI, ISO, ASTM, IEEE, ASHRAE, or
noisy pieces of equipment. A noise specification
others) may be used as a basis for setting up an
equipment noise specification.
would not be necessary for relatively quiet equip-
(1) Sample SPL specifications. Table 9-1 is an
ment that does not dictate noise control design for
example form of a SPL specification. The type of
the MER or the building.
equipment and the desired maximum sound pres-
a. Waiver. If a noise level specification is re-
sure levels are inserted in the appropriate blanks.
quired to be met for a particular piece of equip-
ment, and this becomes a "hardship" on the
The 3 foot distance is taken from the nearest
surface rather than from the acoustic center, since
manufacturer or the owner in terms of cost or
the exact location of the acoustic center is not
availability, the noise specification could be
easily defined. A minimum room volume of 4000
waived, depending on the response of all the
ft. 3 is offered, but this could be modified to accept
bidders. If some bidders agree to meet the specifi-
cation while others do not, this could be a valid
somewhat smaller rooms. Small rooms are more
basis for selecting the quieter equipment. If no
subject to standing wave fluctuations. Even at the
3 foot distance, SPL values for the same source
bidders can meet the specification, the specifica-
may vary as much as 5 to 7 dB from an outdoor to
tion can be waived, but it may be necessary to
an indoor site (or from a large room to a small
reevaluate the noise control requirements of the
room). Since it is impractical to specify Room
MER, if this particular equipment is so noisy that
Constant limits for the measurement room, it then
it is responsible for the noise design in the first
becomes necessary to judge or compare various
place. Of course, it is the primary purpose of this
sound level submittals in terms of their ability to
manual to prevent just such situations as this, as
meet the design need. A sound source measured in
too many waivers would negate the value of the
a large-volume room, in a highly absorbent room,
noise evaluation as a part of the design phase of
or outdoors will produce lower sound levels than
the building. If the equipment measured for this
when measured in a small or reverberant room.
study represents a fair sampling, it is likely that
This difference is an important aspect of compar-
most of the equipment would meet a noise specifi-
ing competitive equipment.
cation.
(2) Sample PWL specification. Table 9-2 is an
b. Sample specifications. The sample noise level
example form of a PWL specification.
specifications given below offer a broad set of
9-2
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