Muffler Classification

Mufflers can be classified into two main types: reactive and dissipative. The design of reactive and dissipative mufflers is reviewed in a number of practical and theoretical books and book chapters [1–15]. Reactive mufflers are composed of one or more chambers and resonators of different volumes and shapes linked together by sections of pipe. They work by reflecting sound waves back from the muffler elements toward the source and back and forth in some of the chambers. This results in an impedance mismatch between the source and the muffler at certain frequencies and also some absorption of energy by nonlinear behavior of the gas. Dissipative mufflers on the other hand are lined with acoustical material which absorbs the sound energy and converts it into heat. It should be noted that some question the common classification of mufflers into reactive and dissipative (reflecting and absorbing types). Moser states that the dominating effect of so‐called dissipative mufflers is not necessarily absorption, since reflection is often of considerable importance [16]. Mufflers can be designed to be partly reactive and partly dissipative and in fact some internal combustion engine mufflers (particularly those for motorcycles) do sometimes incorporate absorbing materials. However, this material can deteriorate because of the severe temperature conditions and become clogged, melt, or fatigue. Thus, most automobile mufflers manufactured today are of the reactive type and do not incorporate absorbing materials. Nevertheless, some dissipation can still occur in a reactive muffler due to viscous dissipation.