Noise diagnosis using nearfield acoustical holography

Abstract

This presentation focuses on diagnosis of air- and structure-borne sounds by using nearfield acoustical holography (NAH) with an emphasis on applications of Helmholtz equation least-squares method for various industrial projects. The presentation is structured with strong consideration towards the end result, which is the visualization and quantification of the acoustic field and ranking of relative contributions from individual noise sources. It is emphasized that, in general, this approach does not deal with actual noise control but rather with identifying the areas where such effort may yield the most cost-effective results. Comparison of NAH-based diagnosis with other techniques such as transfer path analysis and an intensity probe is presented, and their relative advantages and disadvantages are discussed. Specific examples of identifications of sound transmission paths into a passenger vehicle compartment, fuselage of an aircraft, and disk brake squeals are presented. The reconstructed acoustic quantities, such as the acoustic pressures and normal surface velocities, are compared with the benchmark results.