Edgar Choueiri - Academia.edu (original) (raw)
Papers by Edgar Choueiri
Journal of The Audio Engineering Society, Oct 22, 2020
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Journal of The Audio Engineering Society, May 26, 2016
It is often desired that a transducer have a polar radiation pattern that is invariant with frequ... more It is often desired that a transducer have a polar radiation pattern that is invariant with frequency, but there is currently no way of quantifying the extent to which a transducer possesses this quality (often called “constant directivity” or “controlled directivity”). To address this problem, commonly-accepted criteria are used to propose two definitions of constant directivity. The first, stricter definition, is that the polar radiation pattern of a transducer must be invariant over a specified frequency range, whereas the second is that the directivity index (i.e., the difference, in dB, between the on-axis frequency response and the average response over all directions), must be invariant with frequency. Furthermore, to quantify each criterion, five metrics are derived: 1) Fourier analysis of contour lines (i.e., lines of constant sensitivity over frequency and angle), 2) directional average of frequency response distortions, 3) distortion thresholding of polar responses, 4) standard deviation of directivity index, and 5) cross-correlation of polar responses. These five metrics are computed using measured polar radiation data for four loudspeakers. The loudspeakers are then ranked, from most constant-directive to least, according to each metric, and the rankings are used to evaluate, by comparison with each other and with a predetermined “correct” ranking, each metric’s ability to quantify constant directivity. Results show that all five metrics are able to quantify constant directivity according to the criterion on which each is based, while only two of them, metrics 4 and 5, are able to adequately quantify both proposed definitions of constant directivity.
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The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are i... more The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime. 22 refs.
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45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Aug 2, 2009
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Journal of The Audio Engineering Society, Oct 8, 2017
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Journal of The Audio Engineering Society, Oct 8, 2017
A method is developed for efficiently calculating head-related transfer functions (HRTFs) directl... more A method is developed for efficiently calculating head-related transfer functions (HRTFs) directly from head scan point clouds of a subject using a database of HRTFs, and corresponding head scans, of many subjects. Consumer applications require HRTFs be estimated accurately and efficiently, but existing methods do not simultaneously meet these requirements. The presented method uses efficient matrix multiplications to compute HRTFs from spherical harmonic representations of head scan point clouds that may be obtained from consumer-grade cameras. The method was applied to a database of only 23 subjects, and while calculated interaural time difference errors are found to be above estimated perceptual thresholds for some spatial directions, HRTF spectral distortions up to 6 kHz fall below perceptual thresholds for most directions.
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Journal of The Audio Engineering Society, Oct 23, 2015
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Review of Scientific Instruments, Nov 1, 2020
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Journal of The Audio Engineering Society, Nov 22, 2019
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Journal of the Acoustical Society of America, May 1, 2017
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Elsevier eBooks, 2003
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Physical Review Letters, Oct 2, 2019
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Proceedings of Meetings on Acoustics, 2017
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Plasma Sources Science and Technology, Feb 1, 2022
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Physical Review Letters, Nov 23, 2016
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Journal of The Audio Engineering Society, May 4, 2021
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Journal of The Audio Engineering Society, Oct 22, 2020
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Journal of The Audio Engineering Society, May 26, 2016
It is often desired that a transducer have a polar radiation pattern that is invariant with frequ... more It is often desired that a transducer have a polar radiation pattern that is invariant with frequency, but there is currently no way of quantifying the extent to which a transducer possesses this quality (often called “constant directivity” or “controlled directivity”). To address this problem, commonly-accepted criteria are used to propose two definitions of constant directivity. The first, stricter definition, is that the polar radiation pattern of a transducer must be invariant over a specified frequency range, whereas the second is that the directivity index (i.e., the difference, in dB, between the on-axis frequency response and the average response over all directions), must be invariant with frequency. Furthermore, to quantify each criterion, five metrics are derived: 1) Fourier analysis of contour lines (i.e., lines of constant sensitivity over frequency and angle), 2) directional average of frequency response distortions, 3) distortion thresholding of polar responses, 4) standard deviation of directivity index, and 5) cross-correlation of polar responses. These five metrics are computed using measured polar radiation data for four loudspeakers. The loudspeakers are then ranked, from most constant-directive to least, according to each metric, and the rankings are used to evaluate, by comparison with each other and with a predetermined “correct” ranking, each metric’s ability to quantify constant directivity. Results show that all five metrics are able to quantify constant directivity according to the criterion on which each is based, while only two of them, metrics 4 and 5, are able to adequately quantify both proposed definitions of constant directivity.
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The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are i... more The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime. 22 refs.
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45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Aug 2, 2009
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Journal of The Audio Engineering Society, Oct 8, 2017
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Journal of The Audio Engineering Society, Oct 8, 2017
A method is developed for efficiently calculating head-related transfer functions (HRTFs) directl... more A method is developed for efficiently calculating head-related transfer functions (HRTFs) directly from head scan point clouds of a subject using a database of HRTFs, and corresponding head scans, of many subjects. Consumer applications require HRTFs be estimated accurately and efficiently, but existing methods do not simultaneously meet these requirements. The presented method uses efficient matrix multiplications to compute HRTFs from spherical harmonic representations of head scan point clouds that may be obtained from consumer-grade cameras. The method was applied to a database of only 23 subjects, and while calculated interaural time difference errors are found to be above estimated perceptual thresholds for some spatial directions, HRTF spectral distortions up to 6 kHz fall below perceptual thresholds for most directions.
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Journal of The Audio Engineering Society, Oct 23, 2015
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Review of Scientific Instruments, Nov 1, 2020
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Journal of The Audio Engineering Society, Nov 22, 2019
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Journal of the Acoustical Society of America, May 1, 2017
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Elsevier eBooks, 2003
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Physical Review Letters, Oct 2, 2019
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Proceedings of Meetings on Acoustics, 2017
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Plasma Sources Science and Technology, Feb 1, 2022
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Physical Review Letters, Nov 23, 2016
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Journal of The Audio Engineering Society, May 4, 2021
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