Specific sound source analysis for the road ahead

Paul Boughton

'Before-and-after' results show the difference Source Path Contribution (SPC) makes by quickly finding the contributions, from specific components, to the Noise Vibration Harshness (NVH) experienced by the driver and the significance of the NVH path.

SPC determines the sources of the sound - or vibration - perceived by occupants of a vehicle and determines the routes they take. The results include a quantification of the source level, the sensitivity of the path and the contribution of each individual path to the receiver.

But it is only with the recent innovation of time-domain SPC that any type of event, including transient events, can be analysed.

“The best way to analyse the data is in an interactive manner, listening to the contributions, viewing the live spectrum and turning individual contributions or groups of contributions on and off,” says Brüel & Kjær Senior Application Engineer, Dave Bogema.

Consequently, pronounced differences between specific measurement locations on a diesel engine were able to show the origin and frequency components of high-frequency airborne sounds emanating from the turbocharger.

A diesel truck is a very good example to show where time-domain SPC is required, as its characteristic transient sounds make it very difficult to accurately assess, using only traditional frequency-domain analysis. In an example, on a diesel truck, several airborne and structure-borne paths from the engine were measured and analysed using time-domain SPC techniques.

By contrasting spectrograms that show the contributions from different directions, on different locations, with others that show the sensitivity functions of the transmission paths taken by each contribution, it is easy to identify problems.

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