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The correct quantification of airborne sources and their transfer to the vehicle interior noise enables vehicle manufacturers to set system targets and to assess interior noise effects of new or modified systems. Measurements on complete vehicles and on test-beds for body, engine, exhaust, tire, HVAC etc. can then be used to estimate interior noise contributions and choose an optimal level of solutions. This study addresses exhaust tailpipe airborne noise emission in a highly controlled situation; indoors and with an exhaust simulator. Two methods of characterization are compared. One method uses the sound pressure very close to the active source as a source strength combined with pressure transmissibility to estimate the interior noise contributions. The other method uses an inverse estimate of the source volume acceleration and the pressure over volume acceleration transfer for the same purpose. The methods of airborne contribution analysis are briefly described.

The tendency for car engines to reduce the cylinder number and increase the specific torque at low rpm has led to significantly higher levels of low frequency pulsation from the exhaust tailpipe. This is a challenge for exhaust system design, and equally for body design and vehicle integration. The low frequency panel noise contributions were identified using pressure transmissibility and operational sound pressure on the exterior. For this the body was divided into patches. For all patches the pressure transmissibility across the body panels into the interior was measured as well as the sound field over the entire surface of the vehicle body. The panel contributions, the pressure distribution and transmissibility distribution information were combined with acoustic modal analysis in the cabin, providing a better understanding of the airborne transfer.