Identification and analysis of the noise sources of an engine settled in a car using array-based techniques

Engine noise is one of the most important noise sources in a car. This noise is radiated to both the inside and the outside of the car. In this paper, the accuracy of the array based techniques has been compared with the one of sound intensity measurements. Then, the engine noise of a car has been measured at different rotational speeds through array based techniques. At low frequencies, statistically optimised near-field acoustical holography (SONAH) allows an accurate identification of the noise sources. At medium and high frequencies, different beamforming algorithms are compared, choosing orthogonal beamforming because of its better behaviour regarding the influence of the sidelobes and the best resolution and identification of the noise sources. The noise source maps obtained using array based techniques allow to locate in an accurate way the noise sources in the engine settled in a car when it is working at different rotational speeds, performing an efficient analysis of details of a possible noise problem. The noise sources identified are: the engine, the timing belt, the air intake system, the diesel pump and the cylinders and the crank system; all of them were afterwards analysed in detail through their noise spectra.