The carity resonance phenomenon is one of the most important matters that emphasize the interior noise of a car. In order to study this phenomenon, the experiments were carried out by using the two-dimensional model and the acutual car. Moreover, as a method of abating the caving resonance, Helmholtz resonator is employed and its sound absorbing mechanism is examined theoretically and experimentally. As the results, the following are clarified. a)In the car room sound with certain frequency is emphasized and the interior noise is especially enlarged by the cavity resonance. b)The cavity resonance, troublesome as the interior noise occurs in the comparatively low frequency range and is the cause of what is called "closed sound ", and its vibration modes are considered to be (1, 0, 0, ), (2, 0, 0, )and(0, 1, 0). The cavity resonances at high frequency range are out of the question, because absorbing power in the car room is large in high frequency range by the fibrous lining material. c)In the model experiment, as for the cavity resonances in comparatively low frequency range, the reduced frequencies and vibration modes almost coincide with those of the acutual car. That means these phenomena in the acutual car can be inferred from the model experiment. d)Helmholtz resonator would be effective for preventing cavity resonance, if its resonance frequency is designed to coincide with that of cavity resonance. Its effect becomes larger when the volume of th cavity part of the resonator gets larger. e)The sound absorption coefficient of the Helmholtz resonance is the function of its resonator frequency, volume of the cavity part and the quality factor of the resonance in the resonator, as theoretical formula indicates in Ep. (30).
