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Leakage ranking of vehicle cabin interiors is an important quality index for a car. Noise transmission through weak areas has an important role in the interior noise of a car. Nowadays the acoustic leakage inside a cabin can be measured with different techniques: Microphone array-based holography, Trasmission loss measurement, Beamforming analysis, Sound intensity P-P measurements and ultrasound waves measurements. Some advantages and limits of those measurement approaches for quantifying the acoustic performance of a car are discussed in the first part of this paper. In the second part a new method for fast leakage detection and stationary noise mapping is presented using the Microflown PU probe. This method is called Scan & Paint. The Microflown sensor can measure directly the particle velocity which in the near field is much less affected by background noise and reflection compared with normal microphones.

Sound source localization techniques in a car interior are hampered by the fact that the cavity usually is governed by a high number of (in)coherent sources and reflections. In the acoustic near field, particle velocity based intensity probes have been demonstrated to be not susceptible to these reflections allowing the individual panel contributions of these (in)coherent sources to be accurately determined. In the acoustic far field (spherical) beam forming techniques have been used outdoors in the free field, which analyze the directional resolution of a sound field incident on the array. Recently these techniques have also been applied inside cars, assuming that sound travels in a straight path from the source to the receivers. However, there is quite some evidence that sound waves do not travel in a straight line.

A novel measurement tool is developed that is capable to measure the reflection coefficient of acoustic materials in situ and thus in real live situations such as a car. The measurement tool is a combination of two novel methods, the surface impedance method [1], [2], and the mirror source method [3]. The surface impedance method measures the acoustic impedance close to the surface of an acoustic absorbing material. The method is very sensitive for highly reflective surfaces [1], [2], [6]. The mirror source method uses a miniature monopole sound source that is placed close by the acoustic reflecting material. A particle velocity microphone (a Microflown [4], [5]) is placed close to the monopole source in such way that its sensitive direction is aiming at the acoustic reflecting material and its non sensitive direction is aiming at the source. This way it is only measuring the ‘mirror source’: the reflected image of the monopole sound source.