Further Development of the Sound Intensity Method of Measuring Tire Noise Performance of In-Situ Pavements

SUMMARY Through analysis of earlier research and some recent on-road testing it is demonstrated that, with adequate precaution, accurate measurement of tire/pavement noise using on-board sound intensity (SI) can be accomplished with two intensity probes oriented vertically. As in the single probe method, SI is measured in the airflow alongside of a vehicle at locations opposite the leading and trailing edges of the tire contact patch. With the two-probe configuration, these data can be obtained simultaneously, reducing the number of test runs by a factor of two. It has also been found that with a slight risk of more wind induced noise contamination, the use of nose cones for the single probe configuration can be eliminated as long as a windscreen is used to protect the microphones. The use of a single microphone in exposed flow to measure tire/pavement noise sound pressure level (SPL) is not recommended even when fitted with a windscreen or nose cone. Although overall tire noise SPL measured in flow may show little effect of wind noise contamination when very little or no turbulence is present, individual 1/3 octave band levels are very likely effected, particularly when only a windscreen is used. When turbulence is present due such things as the ambient wind conditions, the wake of the vehicle, etc., the background noise due to wind noise contamination increases dramatically. The presence and magnitude of this contamination is difficult to determine and could vary from one test to another.