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Caractérisations acoustiques de structures vibrantes
par mise en atmosphère raréfiée.
Méthodes d'estimation relatives aux fréquences et amortissements des modes propres.
Applications en acoustique musicale.

Abstract : An experimental method is defined for qualifying the structure/light fluid interaction when linear vibrations are assumed. It is based on the comparison between modal frequencies and damping factors measured when the structure vibrates in air and when it vibrates in near vacuum.

We specially focused on the estimation of modal parameters. Two signal processing techniques ---non parametric and parametric--- are implemented for processing a large number of modes automatically. The accuracy of the two estimators is studied in order
to evaluate the uncertainties on damping factors and frequencies; this is essential to compare modal parameters meaningfully. The parametric method turns out to be necessary in order to estimate the partials made of multiple complex exponentials, when
their frequencies are too close to be tractable with Fourier analysis.

The aim of studying the free vibration of thin metallic plates is to validate the experimental procedure : acoustic impedances, radiation efficiencies and other
acoustical quantities, are derived from the measurements for each eigenmode, and are in
good agreement with theory. The radiation ratio for a steel plate, defined as the part of total dissipated power which is radiated, is about 10% for frequencies below the critical frequency and more than 50% above. In the case of the guitar, the string-bridge coupling is described by a mechanical admittance, which eventually
explains why several partials are more damped in vacuum. The radiation ratio of the guitar lies between 15% and 60%, within the 80-2500 Hz frequency range. Finally, signal processing techniques have allowed to acoustically qualify the restoration of the Perpignan's carillon: the tone decay an average of 15% to 25% slower after the restoration.
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https://tel.archives-ouvertes.fr/tel-00011508
Contributor : Bertrand David <>
Submitted on : Tuesday, January 31, 2006 - 6:22:41 PM
Last modification on : Monday, December 14, 2020 - 9:47:37 AM
Long-term archiving on: : Monday, September 17, 2012 - 11:25:22 AM

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  • HAL Id : tel-00011508, version 1

Citation

Bertrand David. Caractérisations acoustiques de structures vibrantes
par mise en atmosphère raréfiée.
Méthodes d'estimation relatives aux fréquences et amortissements des modes propres.
Applications en acoustique musicale.. Acoustique [physics.class-ph]. Université Pierre et Marie Curie - Paris VI, 1999. Français. ⟨tel-00011508⟩

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