The use of near-field acoustical holography (NAH) and partial-field decomposition to identify and quantify the sources of exterior noise radiated from a vehicle

Abstract

Since power-train noise sources are ‘‘hidden’’ within the engine compartment, it is difficult to use NAH to identify the sources and the associated partial radiation fields that create the exterior noise field radiated by a motor vehicle. Integrated near-field acoustical holography (INAH) has been developed to address this concern. INAH represents a combination of NAH, reference microphone selection procedures, and coherence techniques. The procedure entails sensing the sources inside the engine compartment by using an array of reference microphones, and then calculating the associated partial sound fields by using NAH. A key factor in the success of this procedure is the selection of a good reference microphone subset. A selection procedure has been developed by combining condition number and coherence analyses. The partial field determination problem has been approached by using both partial coherence and singular value decompositon (SVD) procedures. It has been found that the partial coherence technique maintains a closer relationship with the physical partial fields than does the SVD procedure, and thus conveys more information than the latter technique. In this presentation, INAH will be demonstrated through identification of the hidden sources and the partial fields that contribute to the exterior noise field of a vehicle.