An indoor sound-power test for light vehicles

Abstract

There is a need to develop sound-power tests as standards for the noise of manufactured products, such as automobiles. For uniformity of testing, the tests have to be independent of the test location. Sound-intensity measurements can be used for this, as has been demonstrated in tests with six automobiles. The sound power of each vehicle was measured for different loads and engine speeds, using a semicircular array of sound-intensity probes rotated around the vehicle on a dynamometer roll. The tests were conducted at Clark Laboratory Services in a large work area with a hard floor and high ceiling, with partially absorbent material on the walls. There were no room resonances apparent in the A-weighted vehicle sound-power spectra. Also, theoretical estimates with point sources in a reverberant room showed that the presence of the walls and ceiling has a negligible effect on the A-weighted sound power of the vehicles. Good agreement was obtained with a standard reference source. The results with the six vehicles indicated that the peaks in narrow-band sound-power spectra can be used to identify noisy components in a vehicle power train. [Work supported by the United States Office of Naval Research.]