(1) Tonal components. For casing and inlet
(2) Engine covers. The engine manufacturer
noise, particularly strong high-frequency sounds
sometimes provides the engine casing with a pro-
may occur at several of the upper octave bands,
tective thermal wrapping or an enclosing cabinet,
but specifically which bands are not predictable.
either of which can give some noise reduction. Ta-
Therefore, the octave-band adjustments of table
ble 2-7 suggests the approximate noise reduction
26 allow for these peaks in several different
for casing noise that can be assigned to different
bands, even though they probably will not occur in
types of engine enclosures. The notes of the table
give a broad description of the enclosures.
all bands. Because of this randomness of peak fre-
quencies, the A-weighted levels may also vary
from the values quoted.
210
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