The effect of air flow on the insertion loss of a side-branch filter.

In acoustic structures part of the sound energy transmitted by a duct is often diverted into sidebranch tubes or resonators. Even a single side branch has an important effect on the transmission of sound in the main duct. The most prominent example of this is an acoustical side-branch filter. Such filters are used in exhaust mufflers, various types of wind tunnels, jet-engine test cells, air-conditioning systems, and other applications where objectionable noise components have to be eliminated