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The present paper focuses on methods for estimating equivalent source positions or “hot spots” on an object to be modelled acoustically. This procedure is the first step in the derivation of an acoustic equivalent source model to be used e.g. in connection with measured acoustic transfer paths. Methods based on Near-field Acoustic Holography as well as the Inverse Boundary Element Method are described and compared. The use of the different methods is illustrated by actual measurements and calculations on a real passenger car exhaust line system.

This work presents an application of airborne source path contribution analysis with emphasis on prediction of wideband sounds inside a cabin from measurements made around a stand-alone engine. The heart of the method is a time domain source path receiver technique wherein the engine surface is modeled as a number of source points. Nearfield microphone measurements and transfer functions are used to quantify the source strengths at these points. This acoustic engine model is then used in combination with source-to-receiver transfer functions to calculate sound levels at other positions, such as at the driver's ear position. When combining all the data, the in-cabin engine sound can be synthesized even before the engine is physically installed into the vehicle. The method has been validated using a powertrain structure artificially excited by several shakers playing band-limited noise so as to produce a complicated vibration pattern on the surface.