1. ABSTRACTThe automobile exhaust system creates continuously changing engine exhaust noise spectra according to the variation in driving conditions, amplified in the muffler system by resonance resulting in the increase of exhaust noise level or rumble noise within cabin. Therefore, it is necessary to suppress the amplification of noise. However, with such an exhaust system in which the length of the exhaust pipes is much larger than the length of the muffler, the resonance of the system greatly changes depending on the setting position of the silencer, as widely known.The authors have analyzed noise suppression characteristics, actually using automobile muffler systems with particular emphasis on these resonance characteristics and predicted the effect of improving practical exhaust system by optimizing the setting position of the silencer. In addition, the authors also confirmed the improved effect of preformance by an experiment with actual devices. This paper describes the results.