ABSTRACT
This chapter introduces the noise reduction, noise rating, and transmission loss, TL, of muffling devices and discusses classification of muffling devices as reactive and dissipative. It examines acoustic impedance for analysis of reactive mufflers and examines pressure drop calculations for reactive mufflers. The chapter considers lined duct silencers as dissipative mufflers and suggests water injection for noise control of exhausts. Muffling devices are commonly used to reduce noise associated with internal combustion engine exhausts, high pressure gas or steam vents, compressors and fans. A commonly used device, often associated with the design of dissipative mufflers for the reduction of high-pressure gas exhaust noise, is a gas diffuser. In the discussion of muffling devices and sound propagation in ducts, the most commonly used and useful type of impedance is acoustic impedance. Commercial mufflers for internal combustion engines are generally of the reactive type. Small gasoline engines are commonly muffled using an expansion chamber and tailpipe.
