Study on The Influence of Extended Inlet with Acoustic Materials on Low Frequency Noise Control

Low frequency noise control of mufflers is usually difficult. Extended inlet can control low frequency noise to some extent, but the influence of compound impedance structure with sound-absorbing materials contained in extended inlet on low frequency noise is not clear enough. Software COMSOL is used to calculate transmission losses of muffler models with different lengths of extended inlets filled with materials and also study the influence on transmission loss when expansion chamber changes. Corresponding mufflers are then made to be experimented on with an impedance tube to obtain actual results of transmission losses. The simulation and measurement are compared and analyzed. We can come to the conclusion that adjusting extended inlet can control low frequency noises effectively and that with a fixed expansion chamber, the transmission loss curve moves to lower frequencies as extended inlet with sound-absorbing materials increases. Experiment results generally agree with the simulation. Key words: muffler; extended inlet; sound-absorbing materials; low frequency noise control