pings and inlet and discharge mufflers, the stand-
ard deviation between the predicted levels and the
measured levels for engine noise sources (normal-
ized to unmuffled or uncovered conditions) ranged
between 5.0 and 5.6 dB for the engine casing, the
inlet, and the discharge. In the data that follow, 2
dB have been added to give design protection to
where "rated MW' is the maximum continuous full-
engines that are up to 2 dB noisier than the
load rating of the engine in megawatts. If the man-
average.
ufacturer lists the rating in "effective shaft horse-
b. Engine source data. As with reciprocating en-
power" ( e s h p ) , t h e M W r a t i n g m a y b e
gines, the three principal noise sources of turbine
approximated by
engines are the engine casing, the air inlet, and the
exhaust. The overall PWLs of these three sources,
MW = eshp/1400.
with no noise reduction treatments, are given in
Overall PWLs, obtained from equations 24
the following equations:
through 26, are tabulated in table 25 for a useful
for engine casing noise,
range of MW ratings.
Octave-band and A-weighted corrections for these
overall PWLs are given-in table 26.
2-9
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