turbocharger. For many large engines, the air inlet
For small engines (under about 450hp), the air in-
may be ducted to the engine from afresh air supply
or a location outside the room or building. The
ductwork, whether or not lined with sound absorp-
tion material, will provide about 1 dB of reduction
of the turbocharger noise radiated from the open
end of the duct. This is not an accurate figure for
ductwork; it merely represents a simple token
value for this estimate. The reader should refer to
the ASHRAE Guide (See app. B) for a more pre-
cise estimate of the attenuation provided by lined
or unlined ductwork. In table 23, "Base PWL"
equals 94 + 5 log (rated hp). The octave-band
values given in the lower part of table 2-3 are sub-
tracted from the overall PWL to obtain the octave-
band PWLs of turbocharged inlet noise.
2-6
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