Muffling devices are commonly used to reduce noise associated with internal combustion engine
exhausts, high pressure gas or steam vents, compressors and fans. These examples lead to the
conclusion that a muffling device allows the passage of fluid while at the same time restricting
the free passage of sound. Muffling devices might also be used where direct access to the
interior of a noise containing enclosure is required, but through which no steady flow of gas is
necessarily to be maintained. For example, an acoustically treated entry way between a noisy and
a quiet area in a building or factory might be considered as a muffling device.
Muffling devices may function in any one or any combination of three ways: they may
suppress the generation of noise; they may attenuate noise already generated; and they may carry
or redirect noise away from sensitive areas. Careful use of all three methods for achieving
adequate noise reduction can be very important in the design of muffling devices, for example,
for large volume exhausts.