Daniel Fernandez Comesana

A scanning method for source visualization and transfer path analysis using a single probe

There are several methods to capture and visualize the acoustic properties in the vicinity of an object. This article considers scanning PU probe based sound intensity and particle velocity measurements which capture both sound pressure and acoustic particle velocity. The properties of the sound field are determined and visualized using the following routine: while the probe is moved slowly over the surface, the pressure and velocity are recorded and a video image is captured at the same time. Next, the data is processed. At each time interval, the video image is used to determine the location of the sensor. Then a color plot is generated. This method is called the Scan and Paint method. Since only one probe is used to measure the sound field the spatial phase information is lost. It is also impossible to find out if sources are correlated or not. This information is necessary to determine the sound pressure some distance from the source, at the drivers ear for example. In this paper, the method of Scan and Paint is enhanced in such way that it is possible to handle partial correlated sources. The key of the novel method is having a pressure microphone at the listener position which is used as a reference sensor. With all this data, it is possible to derive the spatial phase of the sources measured relative to the listening position.

Fast, High Resolution Panel Noise Contribution Method

All surfaces of a cabin interior may contribute to the sound pressure at a certain reference position, e.g. the humans ear. Panel noise contribution analysis (PNCA) involves the measurement of the contribution of separate areas. This is an effective method to determine the effect of apparent noise sources at a specific location. This paper presents the latest developments on particle velocity based panel noise contribution analysis. In contrast to the traditional methods, the particle velocity approach is faster; it requires 3 days instead of weeks. While the theoretical base of the procedure in this paper is similar to previously published particle velocity based procedure, here the measurement protocol has now been simplified dramatically, which has reduced the measurement time even more to less than a day. The method and its implementation are explained in the paper and a full measurement procedure is reported. Four steps are required to determine and visualize the pressure contribution of the vehicle interior. In a first step, probes are positioned on predefined interior surfaces. Special probe mounting have been made to decrease the handling time. 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 run ups are accessible and do not limit the applicability of the method. The third step is the determination of the transfer paths from the panels to a certain listening position. This measurement is done assuming reciprocity. A monopole source is placed on the listener position and the sound pressure is measured at the surface. In a fourth and last step the transfer paths are linked with the operational data gathered in step two. The results are then visualized using the predefined geometry model. This paper describes the measurement of a conventional car with a resolution of 137 panels. Since an array of 46 probes was used step 2 and step 3 are repeated 3 times.

Scan and Paint: Theory and Practice of a Sound Field Visualization Method

Sound visualization techniques have played a key role in the development of acoustics throughout history. The development of measurement apparatus and techniques for displaying sound and vibration phenomena has provided excellent tools for building understanding about specific problems. Traditional methods, such as step-by-step measurements or simultaneous multichannel systems, have a strong tradeoff between time requirements, flexibility, and cost. However, if the sound field can be assumed time stationary, scanning methods allow us to assess variations across space with a single transducer, as long as the position of the sensor is known. The proposed technique, Scan and Paint, is based on the acquisition of sound pressure and particle velocity by manually moving a P-U probe (pressure-particle velocity sensors) across a sound field whilst filming the event with a camera. The sensor position is extracted by applying automatic color tracking to each frame of the recorded video. It is then possible to visualize sound variations across the space in terms of sound pressure, particle velocity, or acoustic intensity. In this paper, not only the theoretical foundations of the method, but also its practical applications are explored such as scanning transfer path analysis, source radiation characterization, operational deflection shapes, virtual phased arrays, material characterization, and acoustic intensity vector field mapping.

Further Development of the PNCA: New Panel Noise Contribution Reference-Related (PNCAR)

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. The new Panel Noise Contribution Analysis Referenced (PNCAR) implements a new post-processing technique which uses a reference sensor in order to extract the relative phase information for the individual panel and frequency of interest. This technique makes it possible to use a limited amount of probes for measuring a whole car interior. Typically 11 probes are used in 11 sessions. Consequently, the methodology becomes more robust and commercially more affordable than conventional PNCA. A real measurement in driving condition was done on the highway in order to validate the methodology. Two different approaches to apply the theory derivations are compared and discussed.

Direct Sound Radiation Testing on a Mounted Car Engine

For (benchmark) tests it is not only useful to study the acoustic performance of the whole vehicle, but also to assess separate components such as the engine. Reflections inside the engine bay bias the acoustic radiation estimated with sound pressure based solutions. Consequently, most current methods require dismounting the engine from the car and installing it in an anechoic room to measure the sound emitted. However, this process is laborious and hard to perform. In this paper, two particle velocity based methods are proposed to characterize the sound radiated from an engine while it is still installed in the car. Particle velocity sensors are much less affected by reflections than sound pressure microphones when the measurements are performed near a radiating surface due to the particle velocitys vector nature, intrinsic dependency upon surface displacement and directivity of the sensor. Therefore, the engine does not have to be disassembled, which saves time and money. An array of special high temperature particle velocity probes is used to measure the radiation simultaneously at many positions near the engine of a compact class car. The particularities of these probes, the mountings used, and the actions taken to cope with disturbances such as airflows are described in this paper. The effective sound pressure is calculated with a particle velocity based transfer path analysis method and a novel sound power based method. To validate these techniques, the data obtained is compared to the results acquired in an anechoic room with a dismounted engine. It is shown that similar results can be obtained with both methods but that the sound power based methodology seems more practical. It is a straightforward and fast approach to characterize the average sound pressure level at certain distance.

Further Development of Velocity-based Airborne TPA: Scan & Paint TPA as a Fast Tool for Sound Source Ranking

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. The method called “Scan & Paint TPA” makes use of only one probe that is swept along the surface. The reciprocal transfer functions are measured by a second sweep with the same probe and a monopole sound source in the driving position. A new methodology for applying “Scan & Paint TPA” in a complex acoustic environment is given along with an experimental validation in a car interior.

Assessing Vehicle Exterior Noise Using a Virtual Phased Array (VPA)

Exterior noise testing is one of the main standardized quality controls required for developing the majority of vehicles. The combination of static tests and on-road measurements provides an essential key to undertaking a successful refinement process. Beamforming techniques using phased microphone arrays are one of the most common tools for localizing and quantifying noise sources across the vehicle body. However, the use of such devices can result in a series of well-known disadvantages regarding, for instance, their very high cost or transducer calibration problems. Virtual Phased Arrays (VPAs) are proposed as an alternative solution to prevent these difficulties providing the sound field is time stationary. Several frequency domain beamforming techniques can be adapted to only use the relative phase between a fixed and a moving transducer. Therefore the results traditionally obtained using large arrays can be emulated by applying beamforming algorithms to data acquired from two sensors. Simulations and experimental data presented in this paper introduce a first approach to use virtual phased arrays for assessing complex noise problems, such as vehicle exterior noise radiation

Integration of an End-of-Line System for Vibro-Acoustic Characterization and Fault Detection of Automotive Components Based on Particle Velocity Measurements

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. This paper presents the practical implementation of an EOL system based on data acquired with a single 3D probe containing three orthogonally placed acoustic particle velocity sensors. Aspects such as installation process, feature extraction, classification, fault detection and diagnosis are hereby discussed. The presented results provide experimental evidence for the viability of particle velocity-based solutions for EOL control applications.

Unidirectional acoustic probe based on the particle velocity gradienta)

This paper presents the foundations of a unidirectional acoustic probe based on the particle velocity gradient. Highly directional characteristics play a key role in reducing the influence of undesired acoustic sources. These characteristics can be achieved by using multiple acoustic sensors in a spatial gradient arrangement. Two particle velocity sensors possessing the figure eight directivity pattern were used in a first-order gradient configuration to yield a unidirectional probe that can reject most excitations originating from both sides and the rear. The effects of key parameters are thoroughly discussed, and the proposed theory is validated in practice.

Experimental Characterization of a Car Window Excited by Turbulent Flow Using Scanning Sound Intensity Techniques

Reducing the aerodynamic noise produced by turbulent flow exciting a car window is one of the current noise control challenges in the automotive industry. Flow separation and later reattachment into a turbulent boundary layer and turbulent wake occur because of flow over the A-pillar and the wing mirror. Experiments have been carried out to represent an idealised wing mirror noise problem using flow over a half cylinder exciting a flat plate. A scanning P-U (pressure-particle velocity) probe was used to measure various aspects of the window response and sound radiation, including the energy distribution of the vibrating surface, the total radiated sound power and hence the radiation efficiency. In addition, experimental results showed that the operational deflection shapes of the car window can be visualized by using scanning particle velocity measurements, obtaining similar results as with step-by-step measurements using a roving accelerometer. The scanning sound intensity maps also proved to be helpful for detecting weaknesses of the initial experimental setup as part of the experimental optimization.Copyright