Range of Frequencies
Absorption mufflers are effective over a broad range of frequencies.
The simplest form of absorption muffler is a duct with sound-absorbing material on the walls. The thicker the material, the lower the frequency that can be reduced. For higher frequencies, the space between the absorbing walls must be made smaller. A large duct must therefore be sub divided into many smaller ones.
Example
Compressors and the diesel engines inside them both may produce strong low frequency noise even if they are provided with effective mufflers at the intake and exhaust.
Control measure
A complete enclosure of damped material lined with sound absorbent will help. The air and exhaust gases must pass through mufflers which are partly made of channels with sound absorbing walls. Doors for inspection must close tightly.
