JPH05288033

PURPOSE:To directly analyze the noise of fluid to be an object of silencing and appropriately silence audible sound according to the analyzed result, in the silencer of an internal combustion engine to silence audible sound by variably controlling resonant frequency. CONSTITUTION:The sound pressure of noise fluid such as exhaust gas of an internal combustion engine 1 is detected by means of a detector 4, and output to a bark filter (critical range width frequency analyzing means) 6. Hereat, the output from the detector 4 is decomposed into a plurality of power spectra at every critical range width, and a critical range width of which the value of power spectrum is maximum is selected. According to the center frequency in the selected critical range width, a drive signal is output from an N/V convertor (conversion means) 7, the duct length L of a communicating part 16 is adjusted so that the resonant frequency of a third chamber 13 as the resonance chamber of a silencer 19 may be approximately synchronized with the center frequency in the selected critical range width, and the sectional area S of an inlet pipe 17 is adjusted so as to make a damping quantity optimum.