Combination mufflers - Theory and parametric study

Both reflective and dissipative silencers have their respective frequency range of good and poor acoustic performances. Reflective types of muffler in general produce more back pressure than the dissipative ones. So, to take advantage of both types of mufflers and to overcome their limitations, they may be combined to give the required performance over a broad range of frequency of interest. In the present paper the combination (or hybrid) muffler is analyzed using a transfer matrix based approach by means of a two-dimensional wave modeling. The present approach can be used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the inherent bulk reaction assumption of the present analysis is illustrated. A parametric study is carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reflective and absorptive portion of combination muffler to attenuation are investigated from the designer’s point of view.