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For many years engineers in the automotive market have struggled to find ways to accurately and efficiently map the noise sources found inside a vehicle. Many techniques, both theoretical and measurement based, have been proposed and used, but there has always been a trade off between accuracy and efficiency. Techniques like sound intensity mapping and Statistical Energy Analysis have proven to be accurate when mapping noise sources in vehicle, but require a large investment in time and money to create a simple, easy to interpret picture showing where dominant noise sources come from. In this paper the authors will introduce and demonstrate a novel technique, spherical beamforming, which can overcome the issue of test time and produce fast, accurate noise maps from the interior of a vehicle.

Wideband Acoustical Holography (WBH), which is a monopole-based, equivalent source procedure (J. Hald, “Wideband Acoustical Holography,” INTER-NOISE 2014), has proven to offer accurate noise source visualization results in experiments with a simple noise source: e.g., a loudspeaker (T. Shi, Y. Liu, J.S. Bolton, “The Use of Wideband Holography for Noise Source Visualization”, NOISE-CON 2016). From a previous study, it was found that the advantage of this procedure is the ability to optimize the solution in the case of an under-determined system: i.e., when the number of measurements is much smaller than the number of parameters that must be estimated in the model. In the present work, a diesel engine noise source was measured by using one set of measurements from a thirty-five channel combo-array placed in front of the engine.