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Microphone arrays used in vehicle acoustics are mainly designed for fast setup and basic evaluation (e.g. using delay-and-sum beamforming) resulting in a restriction to free field environments. Applications in vehicle interiors require advanced source localization techniques taking into account the reflections at the different panels appearing as mirror sources. Coherence filtering techniques allow for the detection of these mirror sources. An additional sensor is placed as a reference close to the main source. This reference signal is used to filter the array signals increasing the overall dynamic range of the acoustic source mapping. The discrimination of the original source and the reflections is obtained by manipulating the impulse responses between the reference signal and all microphone signals.

Many applications in acoustics, such as transfer path analysis and synthesis (the well-known tools for troubleshooting and sound design of vehicle interior or exterior noise), require the measurement of transfer functions. Several methods are available to determine the transfer functions between identified sources and selected receiver locations. For example, transfer functions can be obtained by means of direct or reciprocal measurements. Due to errors and restrictive constraints during the measurements, the results of the two methods differ. The quality of measured transfer functions must be evaluated with respect to the auralization of the synthesized receiver signals or even the auralization of individual noise shares caused by a specific source and transmitted via one or a combination of paths. This paper compares the different measurement techniques of transfer functions in theory and in practice.