Silencers

Abstract

Silencers come in many shapes and sizes and most all of them can be classified into four types: reactive, dissipative, absorptive, and dispersive or diffusive. Reactive silencers do not use sound absorbing materials but instead employ geometric design principles. An example is the Helmholtz resonator. Absorptive silencers use conventional sound absorbing materials. Dissipative silencers utilize flow resistance to reduce flow velocity. Dispersive or diffusive silencers reduce noise by preventing its generation. By diffusing high-velocity turbulent gas flow to a lower velocity less turbulent flow, less noise is generated. Some silencers will combine the action of two or more of the four types within one envelope. Other functions such as water separation, filtering, spark arresting, or heat recovery may be integrated into the silencer as well (Figure 5-1).