TM 5-805-4/AFJMAN 32-1090
Figure C-4. Sound Pressure Levels of Pumps at 3-ft. Distance.
Part C of table C-13 provides a correction factor
provide "shop air" to maintenance shops, machine
for off-peak fan operation. Section 12.0 contains a
shops, and laboratory spaces, or to provide ventila-
detailed analyses of the noise and noise control of
tion system control pressure for large buildings.
ducted ventilation systems.
Larger compressors are used for special industrial
b. Noise reduction from fan housing. The fan
processes or special facilities, but these are not
housing and its nearby connected ductwork radiate
considered within the scope of the manual. The 3
fan noise into the fan room. The amount of noise is
foot SPLs are given in figure C-5 and table C-15.
dependent on both internal and external dimen-
C-14. Reciprocating Engines.
sions of the housing and ductwork, the TL of the
sheet metal, and the amount of sound absorption
In a separate project for the Department of the
material inside the ductwork. Because of so many
Army, a comprehensive study has been made of
variables, there is no simple analysis procedure for
the noise characteristics of reciprocating and tur-
estimating the PWL of the noise radiated by the
bine engines fueled by natural gas and liquid fuel.
housing and ductwork. However, table C-14 offers
In TM 5-805-9/AFM 88-20/NAVFAC DM-3.14,
a rough estimate of this type of noise. These are
details are given for handling these data and for
simply deductions, in dB, from the induct fan
designing noise control treatments for small power
noise. At low frequency, the housing appears
plants at military bases. The noise levels of the
acoustically transparent to the fan noise, but as
engines as sound sources are summarized here,
frequency increases, the TL of the sheet metal
because these engines may be used as power
becomes increasingly effective.
sources in buildings, and their noise should be
C-13. Air Compressors.
taken into account. Typically, each engine type
has three sound sources of interest; the engine
Two types of air compressors are frequently found
casing, the air inlet into the engine, and the
in buildings: one is a relatively small compressor
exhaust from the engine.
(usually under 5 hp) used to provide a high
a. Engine casing. The PWL of the noise radiated
pressure air supply for operating the controls of
by the casing of a natural-gas or diesel reciprocat-
the ventilation system, and the other is a medium-
size compressor (possibly up to 100 hp) used to
ing engine is given by equation C-6:
C-11
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