Jelmer Wind

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.

The acoustic vector sensor: a versatile battlefield acoustics sensor

The invention of the Microflown sensor has made it possible to measure acoustic particle velocity directly. An acoustic vector sensor (AVS) measures the particle velocity in three directions (the source direction) and the pressure. The sensor is a uniquely versatile battlefield sensor because its size is a few millimeters and it is sensitive to sound from 10Hz to 10kHz. This article shows field tests results of acoustic vector sensors, measuring rifles, heavy artillery, fixed wing aircraft and helicopters. Experimental data shows that the sensor is suitable as a ground sensor, mounted on a vehicle and on a UAV.

3D Sound Source Localization and Sound Mapping using a PU Sensor Array

This article considers the application of an array of pressure and particle velocity sensors to acoustical source localization. This approach can r emove a number of disadvantages of the traditional aeroacoustical testing methods because particle velocity sensors are sensitive to the angle of incidence of the incoming sound and whereas pressure sensors are not. Hence, pressure-particle velocity (p-u) arrays tend to hav e a sharper main lobe in the lower frequency range where the phase differences between pressure sensors are small. In the higher frequency range, phased pressure arrays tend to exhibit side-lobes due to aliasing if the sensor spacing is too large. This aliasing prob lem can be alleviated by using particle velocity sensors such that the sources do not need to be localized from phase differences alone. This article describes p-u based source loca lization techniques and the experimental validation of these techniques in an anechoic envir onment using 24 loudspeakers. Various configurations of sensors and source localization m ethods are studied. The spectra of the sources are determined for each of these cases and the results are compared to the actual spectra and to the determined spectrum using a phased pressure array, showing the advantages and limitations of this new approach.

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.

Amplitude, phase, location, and orientation calibration of an acoustic vector sensor array. Part II. Experiments.

An acoustic vector sensor array consists of multiple sound pressure microphones and particle velocity sensors. A pressure microphone usually has an omni-directional response, yet a particle velocity sensor is directional and usually has a response pattern as a figure of eight. Currently, acoustic vector sensor arrays are under investigation for far field source localization and visualization. One of the major practical issues in these applications, however, is to determine the accurate position, orientation and complex (phase and amplitude) sensitivity of each sensor within the array. In this study, a new calibration method is verified with experiments. The method determines all the crucial parameters based on a limited number of measurements with a reference sensor and multiple sound sources located at known locations. The experiments are performed in an anechoic room. The results are promising.

Three dimensional sound source localization and sound mapping using a p‐u sensor array.

An acoustic sensor array, which consists of pressure and particle velocity sensors, is an attractive alternative to phased pressure array because knowledge of the three dimensional (3‐D) particle velocity directly characterizes the direction of the source. Hence, it is possible to localize sources in the low‐frequency range, where the phase difference between pressure sensors is small, and in the high‐frequency range, where aliasing occurs with pressure sensors. This article applies advanced source localization techniques from aeroacoustics to acoustic vector sensors. Several methods are simulated and tested with several configurations and validated using measurement data from an anechoic chamber. The setup to test the algorithms consists of 24 sources that are distributed in 3‐D around the set ups in the anechoic chamber. The sources are uncorrelated driven with white noise. Conventional beamforming methods have been compared with acoustic vector based deconvolution methods and MUSIC algorithms. Four con...

Sound Power Estimation of a Mounted Car Engine

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. A measurement in a non-anechoic engine test room is done to determine the relation between the particle velocity close to the surface of the engine to the intensity at a certain distance. This relation is used to estimate the intensity at lower frequencies from the surface velocity. INTRODUCTION With a Microflown sensor it is possible to measure the acoustic particle velocity directly at a well-defined location. A P-U probe consists of a pressure microphone and a microflown, which makes it possible to measure velocity, pressure, but also sound intensity and sound energy. The particle velocity sensor is made by two hot micro-wires. When a flow pass through the wires one of them is cooled down more than the other. That causes a variation in the electric resistance that is measurable and proportional to the velocity of the flow (fig.1).