ABSTRACT
Silencers and mufflers cover a wide range of noise reduction devices and must be considered one of the most powerful weapons available to the acoustical engineer. There is no technical distinction between a muffler or silencer, and the terms are frequently used interchangeably; i.e., one manufacturer will use a silencer and another a muffler for the same basic configuration. Despite the terms and myriad of configurations, the devices can be broken into three fundamental groups: absorptive/dissipative, reactive, and dispersive. Absorptive silencers contain either fibrous or porous materials and depend on absorptive dissipation of the acoustical energy. Reactive silencers contain no absorbing material but depend on the reflection or expansion of the sound waves with corresponding self-destruction as the basic noise reduction mechanism. The noise reduction of dispersive silencers usually comes from diffusing a high-velocity gas flow into smaller lower-velocity streams. Some silencers combine the elements of two or more types for extended performance.
