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A technique has been developed to evaluate interior wind rush noise during wind tunnel tests of full-size clay models of vehicles. A small, box-like enclosure with acoustic characteristics made similar to those of a typical vehicle interior is inserted into the clay model behind an actual front sideglass. The wind rush noise coming through the sideglass is directly measured by microphones located within the enclosure. The technique can readily detect wind rush noise changes due to body modifications in the vicinity of the windshield-pillar. In addition, the wind tunnel results agree well with those found on-road.

A new experimental procedure, analogous to that used in structural modal analysis, has been developed to perform acoustic modal analysis in three-dimensional cavities. The procedure involves measurement of the vector components of the acoustic particle acceleration using two closely-spaced microphones. Particle acceleration transfer functions are then determined using these measurements referenced to either a third microphone mounted near the source driving the cavity or an accelerometer mounted on this source. Since these transfer functions contain both magnitude and single axis directional information, acoustic mode shape results can be determined unambiguously. This is not the case if acoustic pressure transfer functions are measured. Standard FFT equipment is used to perform the measurements, and the procedure is easily implemented as a “user data acquisition procedure” in standard structural modal analysis software.

Experimental investigations were conducted to identify and quantify the noise mechanisms of individual elements of truck tire tread patterns. The element under study was handcarved into an otherwise blank tread, full-rubber-depth truck tire. The tire was mounted on the GMR Single Wheel Tire Noise Trailer and the noise radiated by the element was measured on-road as a function of position within the contact patch and tire speed using the two-microphone cross-spectral method of measuring acoustic intensity enhanced by position-triggered sampling. This report deals specifically with the noise mechanisms of cross groove type tread elements, which includes both individual cross groove and cross lug elements. The parameters investigated included groove depth, angle of the groove relative to the sidewall, groove shape, and spacing between grooves.