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Interior noise in motor vehicles is essentially influenced by the engine which may contribute via both, structural and acoustic transmission paths. This engine related interior noise components may be controlled deliberately by active control measures without changing any source or transfer paths characteristics. Besides attenuating dominant noise components, the approach may equally be used to optimise interior sounds with respect to sound quality. Based on general considerations how active noise and vibration control measures may effect subjective criteria, the paper gives examples how different, sometimes extremely contrasting noise characteristics may be realised in a given car.

The concept of identifying, characterizing and assessing sound transfer paths from sources to receiving points by applying transfer path analysis (TPA) has been keeping continuous interest since its introduction some 25 years ago. The attractive prospects of TPA-based clues to aimed modifications at particular sound sources and/or sound transmission paths have been confirmed by many successful applications of the approach. Nevertheless, the method still lacks full, undisputed acknowledgement and approval as a widespread tool of sound contribution analysis. Apart from unrealistic early expectations this may be due to considerable measuring efforts to sufficiently describe all relevant sources. For this reason, the instrumental realization of the approach has been subject to continuous modifications to tighten up the procedure and to reduce its measuring and evaluating efforts.