Since the directivity is also related to wavelength
3-3. Reactive mufflers for reciprocating
of sound, large values of roof dimension D have
engines.
higher vertical directivity and therefore a greater
reduction of horizontally radiated sound than do
Reactive mufflers are used almost entirely for gas
and diesel reciprocating engine exhausts. Reactive
smaller values of D. All these variations are repre-
sented in table 31. The total PWL of the sound ra-
mufflers usually consist of 2 or 3 large-volume
diated from a roof is estimated with the use of
chambers containing an internal labyrinth-like ar-
rangement of baffles, compartments, and per-
equation 33, where TL is the transmission loss of
forated tubes and plates. Reactive mufflers smooth
the roof structure and A is the area of the exposed
roof. The horizontally radiated sound power is then
out the flow of impulsive-exhaust discharge and, by
the total PWL minus the table 31 values.
the arrangement of the internal components, at-
3-3
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