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Theses

Vibro-acoustique de la harpe de concert

Abstract : The acoustical and vibratory properties of the concert harp have not been the subject of many studies. The aim of this PhD thesis is to understand and model the vibro-acoustic behaviour of this string instrument.
First, a general description of the instrument is given, from its origins to its current constitution. More attention is then paid to the finger-string interaction when the string is plucked: the analysis of pictures obtained with a high-speed framing camera gives the parameters of an interaction model.
In the second part, the acoustic radiation of the instrument's body is studied. This radiation implies couplings between the soundboard and the soundbox. A modal analysis, along with measures of acoustic velocities in the sound holes, allows the identication of two coupled modes that are characteristic of the vibro-acoustic behaviour of the instrument in low frequencies. A two degrees of freedom discrete model, describing the harp's response around these two modes' frequencies, is developed. Because of the specicities of the system's damping mechanisms, the model's parameters can only be found through an unusual modal analysis method: the appropriation technique. In addition, the far eld acoustic radiation is studied using a microphones array. The equivalent sources method is then applied to identify a range of acoustical monopoles, thus giving an account for the acoustic radiation of the instrument. Finally, in low frequencies, the harp is modeled by two elementary acoustic sources, one on the soundboard and the other one on the sound holes.
The third part is dedicated to the study of the string-soundboard couplings responsible for sympathetic resonances. These couplings are studied using a generic string instrument model made of a clamped beam onto which strings are connected. The state vector formalism and the transfer matrix method are used to describe the propagation of bending and extensional waves in each sub-structure (beam and strings). Coupling conditions between sub-structures lead to the determination of the normal modes of the assembly and to the identication of those which are responsible for the sympathetic vibrations. These sympathetic modes, are then experimentally extracted from the concert harp. The numerous couplings between the strings, caused by these modes, lead to musical waves presenting a large amount of spectral components, of which frequencies can be really close and thus not solved in the same partial. The identication of these components can only be made through signal processing specic techniques that are high-resolution methods.
Prospects of the results obtained throughout this work are then highlighted for possible use in instrument making.
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Contributor : Jean-Loïc Le Carrou <>
Submitted on : Monday, February 26, 2007 - 1:37:02 PM
Last modification on : Tuesday, March 31, 2020 - 3:20:54 PM
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  • HAL Id : tel-00133443, version 1

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Jean-Loïc Le Carrou. Vibro-acoustique de la harpe de concert. Acoustique [physics.class-ph]. Université du Maine, 2006. Français. ⟨tel-00133443⟩

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