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Comportement vibroacoustique des conduits : modélisation, mesure et application aux instruments de musique à vent

Abstract : The effects of wall vibrations of a wind musical instrument on its sound are an important topic, yet not much studied. The vibrations imply various vibroacoustic couplings : duct/internal fluid coupling and duct/external fluid coupling. These two mechanisms and their effects are analysed.
A model describing the vibroacoustic couplings between a vibrating cylindrical duct and the contained air column leads to a value of input impedance which differs from the perfectly rigid case. For most instruments, the effects are very weak. However, couplings are not negligible when the duct is slightly distorted, which is often the case in practise. The disturbance of the acoustic input impedance is maximum when the eigenfrequency of a mechanical mode of the duct (specially ovalling modes) coincides with the one of an acoustic mode of the air column. The theoretical results are compared to input impedance measurements of various vibrating ducts, confirming the model. The wall vibration effects depend on the disturbance level of the input impedance. They vary from slight disturbance of the spectral content to transitions from a periodic regime to a pseudo periodic regime with beats, which are not desirable in a musical context.
The duct/external fluid coupling is investigated in the case of a trobone bell. When excited acoustically, the radiation from the bell left free to vibrate differs from the case where its vibrations are damped by sand. Some small differences of a few decibels are measured at some of the mechanical resonance frequencies of the bell. These radiating modes are efficient from the acoustic radiation point of view.
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https://tel.archives-ouvertes.fr/tel-00366843
Contributor : Guillaume Nief <>
Submitted on : Monday, March 9, 2009 - 5:25:12 PM
Last modification on : Tuesday, March 31, 2020 - 3:20:53 PM
Long-term archiving on: : Tuesday, June 8, 2010 - 8:33:31 PM

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  • HAL Id : tel-00366843, version 1

Citation

Guillaume Nief. Comportement vibroacoustique des conduits : modélisation, mesure et application aux instruments de musique à vent. Acoustique [physics.class-ph]. Université du Maine, 2008. Français. ⟨tel-00366843⟩

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