The details of a new approach for absolute calibration of microphones, based on the direct measur... more The details of a new approach for absolute calibration of microphones, based on the direct measurement of acoustic particle velocity using Laser Doppler Velocimetry (LDV), are presented and discussed. The calibration technique is carried out inside a tube in which plane waves propagate and closed by a rigid termination. The method developed proposes to estimate the acoustic pressure with two velocity measurements and a physical model. Minimum theoretical uncertainties on the estimated pressure and minimum measurable pressure are calculated from the Cramer Rao Bounds on the estimated acoustic velocity amplitude and phase. These uncertainties and the minimum measurable pressure help to optimize the experimental set up. Acoustic pressure estimations performed with LDV are compared with acoustic pressures obtained with a reference microphone. Measurements lead to a minimum bias of 0.006 dB and a minimum uncertainty of 0.013 dB on the acoustic pressure estimation for frequencies 1360 Hz and 680 Hz.
Ce travail porte sur l'étude du rayonnement acoustique d'une plaque "libre-libre-libre-libre". La... more Ce travail porte sur l'étude du rayonnement acoustique d'une plaque "libre-libre-libre-libre". La plaque est excitée par un signal sinusoïdal dont la fréquence est une de ses fréquences de résonance. La vitesse vibratoire normale de la plaque est mesuréeà l'aide d'un vibromètre laser et la vitesse particulaire acoustique est mesurée par Vélocimétrie Laser Doppler (VLD)à 1 mm de la plaque. Les profils des vitesses mesurées sont semblables. Leur comparaison permet d'estimer la composante tangentielle de la vitesse particulaire acoustique.
A new approach for for estimating the acoustic pressure in the near field of a microphone based o... more A new approach for for estimating the acoustic pressure in the near field of a microphone based on non-intrusive direct measurement of acoustic particle velocity is proposed.
This paper discusses a processing technique for laser Doppler velocimetry (LDV) data, enabling to... more This paper discusses a processing technique for laser Doppler velocimetry (LDV) data, enabling to detect and localize in time domain the presence of Doppler bursts in case of acoustic excitation. A joint detection-estimation scheme based on the use of the wavelet transform (WT) realized in the time-scale domain is proposed. The performances of the detector are characterized with ROC (receiver operating characteristic) curves. Finally, the estimator performances are studied by means of Monte Carlo trials obtained from synthesized LDV signals
Real-Time Particle Detection and Velocity Measurement by Means of Laser Doppler Velocimetry
In this paper, the authors describe a technique for laser Doppler anemometry (LDA) data processin... more In this paper, the authors describe a technique for laser Doppler anemometry (LDA) data processing using two Kalman filters in order to detect the presence of particles in the probe volume and to estimate their velocities. This method turns to be suitable for designing real-time integrated velocimeters. A first Kalman filter estimates the magnitude of the Doppler signal and then
Laser Doppler velocimetry (LDV) is a method for measuring acoustic particle velocity in a fluid. ... more Laser Doppler velocimetry (LDV) is a method for measuring acoustic particle velocity in a fluid. This article presents the approximated analytical forms of the Cramer-Rao bounds (CRB) for the velocity parameters estimation. This study shows that these simplified CRB, which give the lower limits of the variance of any estimator, are close to the exact CRB obtained numerically. These expressions can be very useful in order to guide the choice of the data acquisition parameters.
This paper propose a digital calibration procedure for errors compensation of the output signals ... more This paper propose a digital calibration procedure for errors compensation of the output signals of an analogical quadrature demodulation (QD) hardware. This kind of device is used for laser Doppler velocimetry (LDV) measurements in acoustics. The method developed is based on the use of a maximum likelihood estimator (MLE) in order to estimate the amplitudes, the tension offsets, and the phase shift of two quadrature signals. Such a technique provides a good and a simple way for QD calibration.
A new approach for for estimating the acoustic pressure in the near field of a microphone based o... more A new approach for for estimating the acoustic pressure in the near field of a microphone based on non-intrusive direct measurement of acoustic particle velocity is proposed. This method enables the estimation of the acoustic pressure inside a domain located in front of the microphone membrane. The acoustic pressure is calculated using the acoustic particle velocity on the frontiers of this domain and a physical model based on the Green function of the system. Results are obtained using the acoustic velocity measured with Particle Image Velocimetry (PIV) in front of a microphone excited with a plane wave inside a rectangular waveguide. They show that the diffraction of the plane wave by the microphone leads to an increase of the acoustic pressure on the microphone edge in the order of magnitude of 0.1 dB.
Acoustic power¯ow measurements in the resonator of a thermoacoustic refrigerator are described. T... more Acoustic power¯ow measurements in the resonator of a thermoacoustic refrigerator are described. The technique of measurement is based on particle velocity measurement by laser Doppler anemometry (L.D.A.) together with microphonic acoustic pressure measurement. The calibration procedure is explained and results of measurements are compared with analytical results. The L.D.A. technique permits the measurement of acoustic power¯ow at almost any position and for almost any working frequency in the resonator of thermoacoustic devices. #
This paper deals with a new car horn device made of a sound synthesizer and an electrodynamic hor... more This paper deals with a new car horn device made of a sound synthesizer and an electrodynamic horn loudspeaker. It presents an onedimensional model allowing to predict the loudspeaker efficiency and a specific method to estimate experimentally the model parameters. First, this model aims at reducing the time spent in the design process. Second it aims at correcting the sound emitted by the sound synthesizer in order that the listener hears the sound designed for creating the warning message. The study gives a survey of the vast loudspeaker literature. It is based on the conventional electroacoustic approach used for electrodynamic loudspeakers and on wave propagation models used for characterizing acoustic horns. The estimation of the model parameter values is performed using measurements of the electrical impedance of the loudspeaker and of the acoustic impedance of the horn. The model is assessed by comparing the calculated and measured electrical impedances and horn efficiencies. Results show that the model predicts well the horn efficiency up to 2500 Hz, the limitation being due to the horn radiation impedance modelization.
Cette présentation se propose de montrer les résultats récents sur l'adaptation de l'anémométrie ... more Cette présentation se propose de montrer les résultats récents sur l'adaptation de l'anémométrie laser à effet Doppler à l'acoustique. L'analyse du signal Doppler montre que dans le cas d'une excitation sinusoïdale et sans écoulement, le paramètre important est l'indice de modulation que l'on peut directement relier à la vitesse particulaire et à la fréquence. Différentes approches de traitements des signaux Doppler sont présentées et comparées. Il apparaît que pour accéder à des indices faibles, certaines méthodes paramétriques sont les plus prometteuses.
Performance of two acquisition and signal processing systems for acoustic particle velocity measurements
Laser Doppler Velocimetry is used here to measure sinusoidal structural velocities. Two systems f... more Laser Doppler Velocimetry is used here to measure sinusoidal structural velocities. Two systems for signal acquisition and processing, one available commercially and the other being developed in our laboratory, are assessed in detail. Their performance and limitations are evaluated by means of a comparison of the estimated velocities with reference values given by a laser vibrometer. Both systems show close and satisfactory performance up to 2 kHz for rms velocities higher than 1 mm/s.
Measurement of acoustic particle velocities in enclosed sound field: Assessment of two Laser Doppler Velocimetry measuring systems
Applied Acoustics, 2005
The performances of two Laser Doppler Velocimetry (LDV) systems adapted for measuring the acousti... more The performances of two Laser Doppler Velocimetry (LDV) systems adapted for measuring the acoustic particle velocities are assessed in enclosed sound field. This assessment is performed by comparing the acoustic velocities measured by means of LDV to reference acoustic velocities estimated from sound pressure measurements. The two LDV systems are based on a single optical bench which delivers an optical signal called Doppler signal. The Doppler signal, which is frequency modulated, is analyzed by means of two signal processing systems, the BSA (Burst Spectrum Analyser from Dantec) on the one hand, and a system specifically developed for the estimation of the acoustic velocity on the other hand. Once the experimental setup has been optimized for minimizing the errors made on the reference velocities, the assessment is performed and shows that both systems can measure the acoustic velocity in enclosed field in two the frequency ranges [0–4 kHz] and [0–2 kHz] respectively for acoustic velocity amplitudes of 10 mm/s and 1 mm/s.
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Papers by Bruno Gazengel