The values of table 27 maybe subtracted from the
vides a degree of noise control in the horizontal
octave-band PWLs of casing noise to obtain the ad-
direction. Or, in some installations, it may be bene-
justed PWLs of the covered or enclosed casing. An
ficial to point the intake or exhaust opening hori-
enclosure specifically designed to control casing
zontally in a direction away from a sensitive receiv-
noise can give larger noise reduction values than
those in the table.
in noise radiation. Table 28 gives the approximate
c. Exhaust and intake stack directivity. Freq-
effect can be used for either a horizontal or vertical
uently, the exhaust of a gas turbine engine is di-
stack exhausting hot gases.
rected upward. The directivity of the stack pro-