The identification of tire-induced vehicle interior noise

Sound transmission into a vehicle is classified as either airborne of structure-borne sound. From the point of view of noise control, the reduction of noise transferred by different paths requires different solutions. Coherence function analysis is often used to identify transmission paths. However it can be difficult to separate the airborne from structure-borne components. The principle of acoustic reciprocity offers a convenient method for overcoming this difficulty. The principle states that the transfer function between an acoustic volume velocity source and an acoustic receiver is independent of a reversal of the position of source and receiver. The work done on this study involves exciting a stationary tire and measuring the surface velocity of the tire at a number of discrete points. The acoustic transfer functions between each point on the tire and a receiver point are measured reciprocally. Two sets of measurements are then combined to yield a measure of the sound pressure due to a point force on the tire via the acoustic transmission path only. This technique also provides information on the relative contributions of various regions of the tire wall to the resultant noise. Also the sound radiation characteristics, the horn effect, and resonance at the wheel housing are identified through the reciprocal measurement.