Characterization of bridge motions on the violin using polymer sensor technology

Abstract

Recent developments in minimally invasive polymer-film sensors permit the in-situ detection of mechanical vibrations in musical instruments without significantly disturbing the acoustics of the instrument. As an example, we present measurements of vibrations of a violin between the feet of the bridge and the top plate. To this end, calibrated fluoropolymer-film sensors were matched to the geometry of the bridge feet. The forces exerted on the top plate by either bridge foot can be measured separately during excitation of a string with the bow. The differences in amplitude and phase between bass and treble foot vibrations exhibit the distinctly asymmetrical nature of bridge motions, which of course also depend on the string and the note that are being played, respectively. In comparison with the simultaneously detected string vibrations and the radiated sound, the filter characteristics of the bridge are clearly identified in the spectral representation. As the bridge is also the main agent for the coupling from the body to the string, it is suggested that the observed variations in bridge motion are closely connected to the fact that the playability of a violin changes sometimes quite drastically from note to note.