Effect of an expansion chamber on the propagation of sound in circular ducts

The present analysis reveals that the performance of an expansion chamber is greatly affected by the expansion ratio, the sound frequency and to a lesser extent the chamber length. This conclusion was verified experimentally. It is shown that plane-wave theory is valid only at low sound frequencies and small expansion ratios. It is also concluded that expansion-chamber mufflers are efficient in attenuating low-frequency sound, which make them ideal for automotive silencing applications.