Boundary element analysis of three-pass perforated duct mufflers

A boundary element approach is presented to predict acoustic attenuation pe rformance of three-pass perforated duct mufflers. The muffler is divided in to a number of substructures and then the BEM is applied to each one of the se substructures leading to a system of equations in terms of sound pressur e and particle velocity, Using the boundary and continuity conditions, the transfer impedance matrix is obtained between the inlet and outlet of the m uffler, yielding the four-pole parameters and the transmission loss. For a prototype configuration, the predictions of transmission loss from the pres ent boundary element approach and the one-dimensional theory are compared w ith the experimental results. The boundary element predictions match closel y the experimental results throughout the frequency range of interest, whil e the one-dimensional solution shows a reasonable agreement at lower freque ncies and deviate at higher frequencies, The effect of perforation length, porosity, lengths of the expansion chamber and the end cavities, as well as duct extensions into the end cavities on the acoustic attenuation performa nce of three-pass perforated duct mufflers is investigated in detail. (C) 2 000 Institute of Noise Control Engineering.