Experimental study of repeatability errors in 3D sound intensity measurements in narrow frequency bands (original) (raw)
Related papers
3-D Sound Intensity Measurements: Accuracy Enhancements With Virtual-Instrument-Based Technology
IEEE Transactions on Instrumentation and Measurement, 2000
This paper describes a method that allows accuracy and bandwidth enhancements in 3-D sound intensity measurements. Commercial 3-D probes are usually set up with three mutually perpendicular 1-D p-p probes and, thus, arranged with six microphones; although sound intensity can be calculated with 15 independent pairs of transducers, only the three "primary" pairs that are aligned with the coordinate system axes. The other 12 "secondary" pairs consist of mutually perpendicular microphones, which are placed at a distance that is √ 2 times shorter than the primary one. The main idea of the proposed method is to average the intensity that is measured on primary and secondary pairs. This leads to a larger bandwidth, thanks to the shorter separating distance between secondary pairs. The intrinsic p-p method highfrequency sensitivity loss is partially recovered, starting from the theoretical plane wave expression. Measurements of different axes are weighted with coefficients that are computed by optimizing the measurement uncertainty. Errors that are due to the metrological characteristics of the transducers and the effects of environmental conditions are compensated. Experimental results showed that a p-p probe arranged with half-inch microphones that are placed at a distance of 50 mm allows reliable measurements up to 2.5 kHz, whereas a commercial probe bandwidth with the same configuration is usually 1250 Hz.
Uncertainties in acoustic measurements: a case study
A new method for recording the spatial properties of a soundfield, or for generating a synthetic three-dimensional soundfield, is described. The spatial distribution of sound waves passing at a point in space is sampled by means of a number of virtual directive microphones, covering the surface of a sphere. This corresponds to a discretization of the spatial information, which is exactly the spatial equivalent of the PCM sampling of a waveform. Moreover, the influence of the height of the microphone in the calculation of the acoustic parameters was analysed. The measurements were repeated at different height and different position on a transversal line in the theatre, and statistically analysed
The Journal of the Acoustical Society of America, 2005
This paper describes a full vector intensity probe which advances the field of sound intensity and sound source direction estimation using six matched rotating and variable directional microphones. The probe has three pairs of microphones at an equal spacing of 30 mm that are set up in each of the x, y, and z directions and share the same observation point. The calibration method using the rotating microphone system is effective to correct position errors in the y-and z-axes microphone pairs. Sound intensity measurements using the variable directional microphone method can locate with accuracy a sound source, i.e., the structure parts radiating most acoustic energy. The system can find the maximum sound intensity level and beamwidth of the major lobe, and the peak sound intensity levels of the minor lobes. Therefore, a procedure for sound power determination based on minimum measurement data is theoretically and experimentally discussed. Consequently, it is possible to reconstruct only parts of the system emitting the most noise and measure efficiently the sound power level.
Acta Physica Polonica A, 2017
Sound power level of a noise source is determined by means of sound pressure level or sound intensity level measurements performed in accordance to relevant ISO standards. The determination of sound power level according to ISO 3744, 3745 and 3746 standards is used for free field or for approximated free field conditions. Kinds of measurement surfaces, enveloping the noise source, number of microphones and their positions over the measurement surface are stated in the applied ISO standard. The effects of measurement surface and number of microphone positions on the determination of sound power level were investigated theoretically. As a measurement surface; hemisphere, parallelepiped rectangular box and cylindrical surfaces were selected. Key and additional microphone positions were taken into account in the calculations as well. Sound pressure levels of a commercially available reference sound source were measured in hemi-anechoic room using FFT with 4 Hz steps and also at 1/1, 1/3...
One of the main challenges arising from noise and vibration problems is how to identify the areas of a device, machine or structure that produce signicant acoustic excitation. Measurement methods relying on sound intensity are widely used for the localization and quantication of noise sources although they are often limited by the measurement environment. In contrast, the use of a microphone in combination with three orthogonal particle velocity sensors enables the direct acquisition of 3D dimensional sound intensity without the traditional frequency constrains of pressure-based solutions. Furthermore, stationary sound elds can be characterized eciently by means of manual scanning techniques. In this paper, a expanded scanning method is used in combination with a 3D tracking system based on a stereo camera. Acoustic variations throughout space can be then determined by combining the signals acquired with the tracking information of the probe. An overview of the measurement methodology is given along with the evaluation of several practical examples.
3D Acoustic Field Intensity Probe Design and Measurements
Archives of Acoustics, 2016
The aim of this paper is two-fold. First, some basic notions on acoustic field intensity and its measurement are shortly recalled. Then, the equipment and the measurement procedure used in the sound intensity in the performed research study are described. The second goal is to present details of the design of the engineered 3D intensity probe, as well as the algorithms developed and applied for that purpose. Results of the intensity probe measurements along with the calibration procedure are then contained and discussed. Comparison between the engineered and the reference commercial probe confirms that the designed construction is applicable to the sound field intensity measurements with a sufficient effectiveness.
Analysis of noise emitted by an engine using an innovative 3D microphone positioning system
Proc. Inter-Noise 2020, Seoul, Paper 17_4_995, 1-11 , 2020
When making measurements around a noise source with a sound intensity probe, the position of the probe is required to create a noise map. Usually the measurement positions are fixed on 1 paolo.guidorzi@unibo.it 2 luca.barbaresi@unibo.it 3 massimo.garai@unibo.it 4 monica.giovannucci@toyota-industries.eu 5 tommaso.piazza@toyota-industries.eu 6 tommaso.pesso@toyota-industries.eu a grid or are traced with an IR system. In this paper a case study is presented in which an innovative 3D measurement system for the positioning of the sound intensity probe is used. The position detection system uses acoustic waves to locate a point in three-dimensional space. The result is similar to what is obtained with beamforming systems, with the advantage that by carrying out a series of measurements with an intensity probe it was possible to analyse the noise emissions in a very precise and punctual way, with the desired spatial resolution (within the directionality limits of the acoustic waves that is a function of frequency). In addition, the positioning system is economical and requires just a multichannel soundcard and few other components.
Comparisons in the Design and Implementation of Multi-Microphone Acoustic Probes
2011
Many designs exist for multi-microphones probes used to estimate acoustic active intensity and acoustic energy density. Of these, four microphone cubic designs have found wide use. However, there exist 12 ways to use cubic probes to estimate energy density and 16 ways to estimate intensity. This comparative study is a computational investigation of the errors associated with each design. The frequency range of 0 to 1.4 ka is considered. Results are given for only plane wave fields and all angles of incidence are examined. Depending on which quantity is to be estimated (i.e. intensity magnitude, intensity direction, or energy density), a different design is found to perform best. However, the best designs are shown to outperform the other designs by only small amounts.
A new acoustic three dimensional intensity and energy density probe
2012
The acoustic field inside aircraft cavities is very complex. Indeed, there is often a combination of direct, diffuse and modal fields depending on the measurement point and on the frequency band considered. This is directly linked to the fact that different types of sources are present. In such cavities, like a cockpit, sources can be panels radiating not necessary in a normal way, avionics systems, air vents, etc To find efficient solutions to reduce the noise inside aircraft cavities, a good knowledge of the directivity of the acoustic field in the three dimensions is a great advantage. In this frame, a new intensity acoustic probe has been developed to compute acoustic intensity vector and, acoustic density of energy based on four 1/4" microphones measurements around a small sphere. Its originality consists in the possibility to arrange such probes in an antenna. Several calculation methods have been studied to compute those quantities. Results are compared with three uni-d...
Journal of The Acoustical Society of America, 1995
The statistical error in the estimation of one of the directional components in the complex acoustic intensity vector has already been studied. However, in order to completely determine the intensity vector using a six-microphone sound intensity probe, the statistical error in both its magnitude and angle of orientation must be known. The expressions found for these errors require that the covariance between the different orthogonal components be evaluated. Formulations are obtained for both the active and reactive intensity, and these are valid for spectral densities or for a frequency band. The behavior of the statistical error is studied here in •vo dimensions in different types of analytically defined fields. In addition to the difference in pressure and intensity levels, it is also shown that uncertainties in the modulus are related to the coherence between the pressure in the direction of the resultant vector and that the errors in the angle of orientation are a function of the coherence of the pressure in the perpendicular direction. Furthermore, the low-frequency influence of random electronic noise in the circuits of the microphone apparatus is demonstrated. The use of the different formulations for the prediction of statistical errors is discussed.