Powertrain Sound Power Measurement Using a Two-Degree-of-Freedom Positioning Mechanism 891164

An automated positioning mechanism has been developed for sound power measurement of automotive powertrains. The positioning mechanism was designed and built to carry a two microphone sound intensity probe along a cylindrical surface surrounding the powertrain. The fixture is driven by two electrical motors controlled by a small personal computer. Sound intensity is measured as the two microphone probe is swept along the surface. The apparatus was designed to conform to the ANSI Draft Standard S12-21 “Engineering Methods for Determination of Sound Power Levels Using Acoustic Intensity”. Verification and partial qualification of the apparatus was conducted according to the standard for a measurement procedure which used 10 linear sweeps along the cylindrical surface and two circular sweeps on each endcap of the measurement surface. The verification measurements showed the method to be in good agreement with alternative sound power measurement methods. Measurements take approximately 25 minutes and are repeatable within .2 dB for a stationary noise source. Results of verification studies conducted in conditions where the acoustic field was somewhat reverberant and where parasitic noise sources exist were good within the limits of accuracy of the acoustic intensity method.