The Study On Acoustical Property Of Auto Exhaust Muffler

Automobile exhaust system is the most effective component to reduce the engine's noise, which is one of the primary parts of automobile noise sources, so the exhaust system is very important in noise control of automobile and city. In general, a complicated muffler is disassembled into some anechoic units and every unit can be depicted by two parameters: sound pressure and volume velocity. An anechoic unit is equivalent to a four-pole network and represented by a transmission matrix in the calculation. In this paper, the total transmission matrix of parallel connection anechoic units is deduced in accordance with acoustical theory and four-pole networks. Acoustical property of cross-flow muffler is investigated according to sound propagation theory. The transmission matrix is deduced by establishing equivalent modal and dividing the perforated pipe into finite elements. Considering the resonance and expansion chamber of perforated pipe, its theoretic model is developed and perfected according to acoustic transfer theory. The acoustical model of perforated pipe with sound absorption material is studied and the anechoic performance is attained by calculation of the compound acoustical impedance of the pipe's inside surface. Transmission loss of the anechoic units studied in this paper is attained by the muffler test system. The accuracy of these methods is validated by contrasting with the experiment data.