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In recent years the increase of computer data processing power has facilitated the use of several multi-channel techniques for noise source location and ranking. These techniques include Spatial Transformation of Sound Fields (STSF) and Inverse Boundary Element Method (IBEM) for reconstruction of the sound field on the source surface from near field measurements and Beamforming for far field measurements. STSF and IBEM are suited for the low to medium frequency range whereas Beamforming is suited for the medium to high frequency range. The array methods are briefly introduced and a discussion of the advantages and limitations of the different techniques is presented. Benefits of combination of different techniques are also considered and exemplifying measurements are presented.

Ever stricter legislation is compelling vehicle manufacturers to reduce external vehicle noise. There is, for example, a recommendation before the European Commission that vehicle drive-by noise be reduced to 74 dB(A) for cars and light trucks to take effect from October 1994. Engine manufacturers are therefore exposed to an increasing demand to produce quieter products. This paper explains how certain companies are employing the Spatial Transformation of Sound Fields (STSF) technique to address this problem. A brief introduction to the main principles of STSF is given followed by a number of practical examples of measurements on engines in test cells.

Noise levels and noise characteristics in a car cabin are important competitive discriminators in the automotive industry today. Efficient tools for mapping and analyzing the underlying source distributions are therefore very important for automotive manufacturers. The present paper describes a system based on a hand-held microphone array with integrated position measurement and using the Statistically Optimal NAH (SONAH) calculation method to perform patch holography. The SONAH method has the big advantage as compared to traditional NAH that spatial window effects are small even when the measurement area does not fully cover the source area. The paper also presents practical measurements.