Effects of Higher Order Mode Waves on Muffler Performance

The existence of higher order mode waves (HOMW) in expansion mufflers is proved theoretically. The 3 - D finite element method is used to obtain the four-pole parameters of a muffler which are in turn used to calculate the transmission loss. With this method, the distribution of sound pressure in a muffler is obtained, the effects of HOMW on the muffler performance are investigated and a technique to improve the muffler performance is put forward. It shows that, because of HOMW, the sound wave in expansion chamber is not in plane form; HOMW can decrease the capability of muffler; and the positions of inlet and outlet are important to the performance of mufflers.