Indendification of Noise and Vibration Source Using Acoustic Double Holography Method

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Several kinds of the sound noise source identification techniques have been so far proposed in the noise control and noise reduction technologies, in particular, in the field of transport and vehicle engineering. Among those, acoustic holography methods based on the backward propagation of sound have been investigated for getting high ad accurate resolutionability in the noise source identification. For example, the nearfield acoustic holography (NAH) method was proposed for this purpose utilizing the detection of evanescent wave components in nearfield of the source^<(1)>. However, the detection of the evanescent wave in this method requires nearfield setting of the measuring devices and also somehow complicated analytical instruments for measured data.The acoustic double holography (ADH) method proposed in this paper is a further developed and simplified approach which could vealize higher resolution of the identified noise source plane over conventional acoustic holography (AH) methods. The ADH method basically makes use of dual measuring planes and dose not require nearfield measuring devices and complex analysis such as NAH methods. This Method can be applied to the sound noise identification of various types of transport systems including engine noise detection under operating condition without specific test-treatment for the measuring devices.Thorough these works, following conclusions are obtained.(1) The acoustic double holography (ADH) method can provide higher resolutionability in the noise source identification compared with the conventional AH method.(2) The ADH measurement can be realized in far distant area from unit wave length and measuring time can be determined as same as that in the conventional method.(3) Simple instrumentation of the ADH measuring system can be given in the ADH approach.