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The Panel Noise Contribution Analysis (PNCA) is a well-known methodology for an airborne Transfer Path Analysis (TPA) in car interior. Pressure contribution from the individual panels at a reference point can be very accurately calculated. Acoustic Trim package treatment can therefore be optimized in terms of frequency and panel area which saves money and time. The method uses only one type of sensors so called particle velocity probes for measuring source strength as well as transfer function (with a reciprocal measurement). Traditionally the PNCA makes use of a big amount of probes at fixed points (about 50) hence non-stationary conditions can be measured as well. Typically the measurement is performed in 3 sessions resulting in 150 individual panels. Because of the low spatial resolution the method can only be used at mid-low frequency range.

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.

The particle velocity field close to a source almost matches the surface vibration whereas the sound pressure field is mainly caused by the background noise. Here a new method is proposed that is to simply listen to the particle velocity field to find sources. The method shows to give a very fast first impression of the acoustic problem at hand.

For compliance test purposes, the noise level of a HVAC is usually measured with a pressure microphone positioned at a certain distance. This measurement is normally performed in an anechoic room. However, this method doesn't provide the engineer any insight on what noise sources do contribute to the overall noise level measured. A new Microflown based low sound level source path contribution analysis measurement approach is presented to pinpoint the various noise sources that vary in time, frequency and place. The new method shows all place and time dependent noise sources, and allows assessment of the extent that they contribute to the overall noise level determined for the compliance test using the sound pressure microphone. Furthermore, the new method can be used in a normal room, eliminating the need to use an anechoic room.

Monopole sound sources (i.e. omni directional sound sources with a known volume velocity) are essential for reciprocal measurements used in vehicle interior panel noise contribution analysis. Until recently, these monopole sound sources use a sound pressure transducer sensor as a reference sensor. A novel monopole sound source principle is demonstrated that uses a Microflown (acoustic particle velocity) sensor as a reference sensor. As compared to a sound source that uses a sound pressure transducer as a reference sensor, the new sound sources demonstrated are relatively easy to calibrate, not sensitive to changes in ambient temperatures, and suitable to use in all sorts of acoustic environments.

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.

Acoustic particle velocity sensors can be an alternative sensor category for end of line testing next to microphones, accelerometers or scanning laser vibrometers. As any other category of transducers, particle velocity sensors have their specific features. The acoustic particle velocity field is far less susceptible to background noise than the sound pressure field, allowing acoustic testing to be carried out in a manufacturing environment with significant background noise levels [2]. Close to a vibrating surface, acoustic particle velocity is a good estimate of the normal structural velocity, allowing non contact vibration measurements [4]. The results of some case studies will be summarized.

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.

This paper presents new developments on hot wire anemometer based panel noise contribution analysis. The used sensor allows the direct measurement of particle velocity. Some historical remarks are given and the latest developments of the technique are reported. Four steps are required to determine the panel noise contribution of the interior of a vehicle and to visualize the results in 3D. In a first step the probes are positioned on the interior surfaces and their x, y, z coordinates are measured. Based on these data a 3D geometry model is created. The geometry data are acquired using a specially designed 3D digitizer. The second step is a measurement in a certain mode of operation. This step can be done in a laboratory but it is also possible to perform the measurement whilst driving the vehicle on the road. Stationary as well as non stationary running conditions like e.g. run ups are accessible and do not limit the applicability of the method.

The NVH optimization process of a power train often consists in a target setting for the acoustic power radiation of the engine in free field working conditions (in an anechoic or semi-anechoic room). This method requires the engine to be dismounted from the car and to be measured in an anechoic or semi-anechoic room which is costly and time consuming. Moreover the free-field characterization is not a good predictor of the acoustic behavior of the power train when it is mounted in the engine bay of a car (very reactive field). This paper presents a number of existing methods to determine the acoustic power radiation pattern of the engine mounted in a car using an intensity probe which is based on a pressure sensor and a particle velocity sensor. For the lower frequencies the velocity probe is used, for the higher frequencies both pressure and velocity is used to measure intensity. A new method for the mid-low frequency range is presented.

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.

The interior noise of a car is a general quality index for many OEM manufacturers. A reliable method for sound source ranking is often required in order to improve the acoustic performance. The final goal is to reduce the noise at some positions inside the car with the minimum impact on costs and weight. Although different methodologies for sound source localization (like beamforming or p-p sound intensity) are available on the market, those pressure-based measurement methods are not very suitable for such a complex environment. Apart from scientific considerations any methodology should be also “friendly” in term of cost, time and background knowledge required for post-processing. In this paper a novel approach for sound source localization is studied based on the direct measurement of the acoustic particle velocity distribution close to the surface. An airborne transfer path analysis is then performed to rank the sound pressure contribution from each sound source.

It has been shown that the combination of a particle velocity (u) sensor and a sound pressure (p) microphone can successfully be used to determine the reflection coefficient of acoustic materials [1, 2, 3 and 4]. In this paper, a practical measurement technique and a so called pu-probe impedance meter are described that require no Kundt's tube or anechoic room. The procedure allows fast (less than 60 seconds) sound absorption measurements under both normal and oblique angles of incidence on small test samples (less than 30*30cm). The total size of the pu-probe impedance meter is 60 centimeters and weights less than 1kg. The method can be used in combination with a sound card based software package. At first, the pu-probe is calibrated in approximately 20 seconds. The frequency response of the impedance sensor is transformed to an impulse response. This response is time windowed to cancel out the room reflections.

In order to reach OEMs acoustic treatment targets (improving performance while minimizing the weight and cost impact), we have developed an original hybrid approach called “Vehicle Acoustic synthesis method”[1] to simulate - and therefore to optimize - noise treatments for both insulation and absorption, and to calculate the resulting Sound Pressure Level (SPL) at ear points for the middle and high frequency range. To calculate the SPL, we identify equivalent volume velocity sources from intensity measurements, and combine them to acoustic transfer functions (panel/ear) measured or computed with ray tracing codes using the reciprocity principle. Compared to our first approach [1], this paper shows a new measurement technique using pressure-particle velocity probes [2]. This technique allows to reduce acquisition time by a factor four, and makes therefore possible a synthesis method on a complete car within two weeks.