TM 5-805-4/AFJMAN 32-1090
Table C-15. Sound Pressure Levels (in dB at 3-ft. Distance) for
Lw = 93 + 10 log (rated hp) + A +
Air Compressors.
B+C+D,
(eq C-6)
where Lw is the overall sound power level (in dB),
Octave
Air Compressor Power Range
"rated hp" is the engine manufacturer's continu-
10-75 hp
ous full-load rating for the engine (in horsepower),
1-2 hp
3-9 hp
Band
(bB)
(Hz)
(dB)
(dB)
and A, B, C, and D are correction terms (in dB),
given in table C-16. Octave band PWLs can be
31
87
92
82
obtained by subtracting the table C-17 values
63
81
84
87
from the overall PWL given by equation C-6. The
125
81
84
87
octave band corrections are different for the differ-
250
80
83
86
ent engine speed groups. For small engines (under
about 450 hp), the air intake noise is usually
500
83
86
89
radiated close to the engine casing, so it is not
1000
86
89
92
easy or necessary to separate these two sources;
86
2000
89
92
and the engine casing noise may be considered as
4000
84
87
90
including air intake noise (from both naturally
8000
81
84
87
aspirated and turbocharged engines).
b. Turbocharged air inlet. Most large engines
A-weighted,
have turbochargers at their inlet to provide pres-
dB(A)
91
94
97
surized air into the engine for increased perfor-
mance. The turbocharger is a turbine driven by
Table C-16. Correction Terms (in dB) to be Applied to Equation C-6 for Estimating the Overall PWL of the Casing Noise of a
Reciprocating Engine.
C-14
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