Cavity Resonance and Noise Reduction in a Rotary Compressor

Of the noises radiated from home refrigerators, freezers, and air conditioners, the noise due to cavity resonance in the compressor shell is of the highest level. For clarifying the nature of this noise and developing an effective method of reducing it, some theoretical and experimental analyses were performed. As a rst step, the resonant frequency and sound field characteristic within the shell were analyzed by simulating the cavity, defined by the outer surface of a compressor mechanism, and the inner surface of its shell structure to a simple concentric double cylinder model. Then a special muffler was devised in accordance with the results of the analyses. As a second step, a sound source simulation test and a noise measurement in the experimental compressor refrigeration system were performed. In the sound source simulation test, a muffler was mounted on the mechanism over the discharge port of the 3/4-hp Rolling piston-type refrigerant compressor and a speaker driven with a pure-tone oscillator was connected to the discharge port, and the transfer functions were measured with three microphones. The test demonstated that the noise in the compressor shell is derived from cavity resonance and that the transfer function, and hence the magnitude of noise reduction, depends on the relative position of the muffler outlet and the discharge port.