Application of patch contribution analysis to a motorcycle engine

The theory of patch (or panel) contribution analysis is first reviewed and then applied to a motorcycle engine on a test stand. The approach is used to predict the sound pressure in the far field and the contribution from different engine components to the sound pressure at a point. First, the engine is divided into a number of patches. The transfer functions between the sound pressure in the field and the volume velocity of each patch were determined by taking advantage of vibro-acoustic reciprocity. An inexpensive monopole source is placed at the receiver point and the sound pressure is measured at the center of each patch. With the engine idling, a p-u probe was used to measure particle velocity and sound intensity simultaneously on each patch. The contribution from each patch to the target point is the multiplication of the transfer function and the volume velocity, which can be calculated from particle velocity or sound intensity. There were two target points considered. The first was 5 feet away from side of the test rig and the other was approximately at the position of the driver's ear. The sound pressure in the field was reconstructed assuming both correlated and uncorrelated monopole sources. In addition, the contributions from engine, primary housing, transmission housing, and exhaust were compared.