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Tests were conducted with a range of six light vehicles, provided by the auto industry, using a measurement system consisting of a semi-circular array of sound-intensity probes rotated around the test vehicle on a dynamometer roll. Measurements with this system showed good agreement with a standard reference source. The results with the six vehicles indicated that it is possible to develop an indoor sound-power test, as a standard of motor vehicle noise, that would be an alternative or replacement for the existing outdoor passby tests. Such an indoor test avoids the cost of delays due to bad weather, and is more convenient for noise tests of vehicles under development in indoor work areas, The results also indicate that the peaks in the narrowband sound-power spectra occur at frequencies of the orders of excitation of the various components of the power train.

Various SAE vehicle noise test subcommittees have been involved in numerous programs to improve and expand the applicability of procedures for increasing exterior noise levels and their relationship to the ever changing product lines. Parallel to this work, governmental and trade associations have also sought changes to better reflect the true measure of noise impact on the community. The evolution of testing has resulted in a continuing improvement in the quality of the test data. Benefits from the combined test programs have resulted in a significant improvement in the understanding of the test variability, statistical reliability, and applicability of these procedures. This paper will provide a compendium of the modifications that have evolved into the noise measurement procedures and practices in use today. The major emphasis will focus on passenger cars and light trucks.