Using mechanical-acoustical reciprocity for diagnosis of structure borne sound in vehicles

Abstract
The low frequency interior noise in cars is for a large part the result of structure bome excitation. The transfer of the structure bome sound involves a large number of components of the engine suspension, wheel suspension and chassis which are all potentially contributing to the overall noise level. This process can be analyzed through a combination of transfer function measurements with operational measurements under normal vehicle conditions. This technique, called transfer path analysis, requires large numbers of transfer function measurements with excitation of the body or cabin at the rubber mountings. Unfortunately, bad access to these crucial measurement locations causes either high instrumentation and measurement effort or less accurate measurement data. The practicality and quality of the measurements can be improved by using reciprocal measurements for the mechano-acoustic transfer of the body or cabin structure ; a loudspeaker in the cavity is used for the reciprocal excitation. The reciprocity technique also allows better insight in the acoustic response of the cavity.