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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.

Tip-in/Tip-out of the accelerator pedal generates transient torque oscillations in the driveline. These oscillations may be amplified by P/T, suspension and body modes and will eventually be sensible at the receiver side in the vehicle, for example at the seat or at the steering-wheel. The forces that are active during this transient excitation are influenced by non-linear effects in both the suspension and the power train mounts. In order to understand the contribution of each of these forces to the total interior target response (e.g. seat rail vibration) a detailed investigation is performed. Traditional force identification methods are not suitable for low-frequent, transient phenomena like tip-in/tip-out. Mount stiffness method can not be used because of non-linear effects in the P/T and suspension mounts. Application of matrix inversion method based on trimmed body vibration transfer functions is not possible due to numerical condition problems.