Paramètres physiques d'un oscillateur changés par contrôle actif. Application à la lame de xylophone

International audienceOn the input admittance of many violins a typical broad frequency peak, called "bridge hill" appears around 2.5 kHz. The physical parameters of a violin bridge have a significant influence on this feature, and then on the tonal colouration of the produced sound. The effect of the bridge characteristics (mass, stiffness and foot spacing) on the frequency response have been revealed by using bridge models through several studies. Here the parameters of the bridge response are changed, by applying an active control method. Such a correction, very useful in noise reduction, enables to change separately the position and the shape of the bridge hill. It is first tested on a simplified bridge model, then on a real bridge by placing 2 actuators and an accelerometer at strategic positions

Techniques de Focalisation par Retournement Temporel dans le Domaine Audible

National audienceCetté etude présente les propriétés de focalisation acous-tique spatio-temporelles par retournement temporel (RT) dans le domaine audible en fonction de l'environnement dans lequel l'expérience est menée. La possibilité de réaliser une focalisation par RT grâcè a un miroir com-posé d'un transducteur sera démontrée dans un milieu réverbérant. Malgré leuréléganceleurélégance et leur adaptivité, ces méthodes de focalisation ne permettent pas de focaliser en super-résolution. Le puits acoustique, pour la première fois mis en place dans le domaine audible permet, lui, d'obtenir une résolution accrue par rapport à la focalisation par RT classique et de vaincre la limite physique de diffraction imposée par cettedernì ere. Nos résultats expérimentaux montrent la possibilité de créer une tache focale à λ/7

Active Control of Violin Bridges

International audienc

Active Control of Violin Bridges

International audienc

A modal method adapted to the active control of a xylophone bar

International audienc

Acoustic portrait of four clavichords : tangent velocities, loudness and decay times

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Acoustic portrait of four clavichords : tangent velocities, loudness and decay times

International audienc

Modifying the Resonances of a Xylophone Bar Using Active Control

International audienceAs imple active control method is described which extends the possibilities of ax ylophone bar.I ta llows the performer to modify the vibration of its structure, unlikepost-processing effects involving loudspeakers. These variations change the characteristics of the partials radiated by the bar.T he xylophone bar,m ade of composite material, is equipped with twoactuators and one sensor in PVDF (polyvinylidene fluoride), the mass and stiffness of which do not modify the mechanical characteristics. Ac ontroller in af eedback loop is executed on am idrange digital signal processor.I ti sc omposed of as um of second order band-pass filters. The selection of the controller coefficients relies on the measured transfer function between the input of the controller and the output of the sensor.F irst the active control method is designed to modify the resonance peaks of as imple model of ax ylophone bar,w hose transfer function is as uperposition of three eigenmodes. Then it is applied to the real system. It is illustrated by increasing and reducing the amplitudes and/or frequencies of the first resonances, and by modifying the tuning of the xylophone bar

Super-resolution imaging of active sound and vibrational sources using a time-reversal sink

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