Indoor System for Efficient Measurement of the Sound Power of Light Vehicles and for Noise-Control Diagnostics

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. This identifies noisy components and also provides a quantitative measure of how much the total sound power can be reduced by reducing the noise of these components.