Reciprocity Technique for Analysis of Road Noise of Vehicles. 1st Report. Measurement of Mechanical-Acoustic Transfer Functions.

Abstract

A technique based on the reciprocity principle has been developed for measuring mechanical-acoustic transfer functions for vehicle road noise induced by forced displacement inputs from the suspension. With this technique, acoustic excitation is applied to the car body and the resulting constraint force of the tires are measured by means of tri-axial load cells with a loudspeaker installed at the driver's ear position. This paper will first explain the mechanical-acoustic reciprocity principle corresponding to forced displacement excitation. Empirical examples will then be given of applications of this technique to the reduction of low-frequency road noise of a passenger car. The results indicated that the reciprocity technique is applicable to a fully trimmed vehicle that includes an engine and suspension and is often cheaper and more convenient than the equivalent shaker-based excitation method for measuring mechanical-acoustic transfer functions.