A type of combined reactive/dissipative muffler is a plenum chamber which is a large
volume chamber which connects two ducts. The interior of the chamber is lined with sound
absorbing material, and thus part of the high frequency sound energy which enters the chamber
is absorbed due to multiple reflections within the unit, while the low frequency energy is
reflected or suppressed because of the sudden expansion and contraction in effective duct crosssectional
area as a result of the presence of the chamber. An example of a reactive muffler is
shown in Figure 10.25, dissipative mufflers are shown in Figures 10.26(a)-(d), and a combined
reactive / dissipative muffler is shown in Figure 10.27.