Corde frottée sur un violon: Dynamique, mouvements standard et instabilités

Bowed string dynamics: standard motions and instabilities. A bowed string is self-oscillating in response to the nonlinear friction of the bow upon the string. The periodic, so-called Helmholtz motion which is sought by musicians is characterised by a succession of one sticking phase and one slipping phase per period. Perturbations may superimpose onto this movement and be the cause of aperiodicities which might eventually be heard as musical disturbances. Accounting for the quality of a violin requires that a thorough understanding of the phenomenon be achieved: tribology of rosin, torsional waves on the string, mechanical mobility of the bridge. The stability of the Helmholtz motion, the conditions to reach it after an initial transient, the discrepancies from the ideal motion are analysed and other motions are presented.