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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.

In order to apply an effective noise reduction treatment determining the contribution of different engine components to the total sound perceived inside the cabin is important. Although accelerometer or laser based vibration tests are usually performed, the sound contributions are not always captured accurately with such approaches. Microphone based methods are strongly influenced by the many reflections and other sound sources inside the engine bay. Recently, it has been shown that engine radiation can be effectively measured using microphones combined with particle velocity sensors while the engine remains mounted in the car [6]. Similar results were obtained as with a dismounted engine in an anechoic room. This paper focusses on the measurement of the transfer path from the engine to the vehicle interior in order to calculate the sound pressure contribution of individual engine sections at the listener's position.

With PU probes the sound pressure and acoustic particle velocity can be measured directly. Over recent years, the in situ surface impedance method, making use of such a probe, has proven to be an alternative to Kundt's tube measurements for product development type of work. The in situ method can also be used for the purpose of quality control on the acoustic material, be it during manufacturing or assembly, ensuring the best possible way to monitor the practical effectiveness of the acoustic package designed earlier on. In order to assess the variance of the acoustic package material leaving the assembly line, a relevant number of samples were taken over time. The quality of both the headliners, and the passenger seats were measured, of 25 cars of the same type. The robustness of the measurement method will be discussed, and the results will be presented.

The automotive industry is currently increasing the noise and vibration requirements of vehicle components. A detailed vibro-acoustic assessment of the supplied element is commonly enforced by most vehicle manufacturers. Traditional End-Of-Line (EOL) solutions often encounter difficulties adapting from controlled environments to industrial production lines due the presence of high levels of noise and vibrations generated by the surrounding machinery. In contrast, particle velocity measurements performed near a rigid radiating surface are less affected by background noise and they can potentially be used to address noise problems even in such conditions. The vector nature of particle velocity, an intrinsic dependency upon surface displacement and sensor directivity are the main advantages over conventional solutions. As a result, quantitative measurements describing the vibro-acoustic behavior of a device can be performed at the final stage of the manufacturing process.

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.

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.