Break-out noise from the shell often puts a limit on the (net) transmission loss that can be obtained from an engine exhaust muffler. One of the best ways of reducing break-out noise is use of a sandwich plate shell. This short paper presents an analytical model for prediction of transverse transmission loss of sandwich plate shells. Four-pole parameters of the porous layer are used along with an impedance approach for relating radial velocity of the outer (exposed) metallic layer to acoustic pressure of a plane progressive wave inside the muffler shell. This is combined with radiation impedance for outgoing cylindrical waves to predict transverse transmission loss. Thus, a sandwich plate shell is compared with a single layer shell without and with wrapping of another metallic layer by means of a transverse insertion loss. Finally, results of a parametric study are reported to help the muffler designers.
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