On Thu, 10 Jan 2002 12:01:59 Ron Nossaman wrote: > >http://www-ccrma.stanford.edu/~jos/waveguide/Dynamic_Terminations.html > > >When a traveling wave reflects from the bridge of a real stringed >instrument, the bridge moves, >transmitting sound energy into the instrument body. How far the bridge >moves is determined by the >driving-point impedance of the bridge, denoted . The driving point >impedance is the ratio >of Laplace transform of the force on the bridge to the velocity of motion >that results . > >Ron N > Ron, I don't know if you saw a reference I gave last week about the violin bridge. I thought the point of it was that the violin top is physically moving in direct response to the input from the string, but no one seemed to notice. I went back and had another look. Here's the reference: http://www.speech.kth.se/qpsr/tmh/96-4-009-013.pdf They measure the movement of the violin top with holography and also with accelerometers. The resolution of the equipment appears to be .1 milliseconds or one ten thousandth of a second. The motions of the string and bridge and top which they detect seem to occur over much larger periods of time than this so this should give a pretty good indication of what's going on. Here are a few quotes: The time history of the body deflections from impulse excitation of a violin has holographically been registered. Deformations resulting from the initial impulsive force... A resulting initial motion of dipole character in the top plate... For the impulse excitation as in fig 1, the top plate bulges at the treble foot and curves in at the bass foot. The bulging and curving in start at the bridge feet and grows thereafter both in height and width... The bulging and curving in represent a travelling wavefield.. After some time, reverberating standing waves show up... -- Also there are some graphs showing velocity measured at the bridge feet. ----- I interpret this to mean that the bridge and top are moving in direct response to the input from the string. This paper is not intended as a general reference on how the violin works, but as a report on the investigation of a specific aspect of violin behavior. When I have time I'll review some more general references. Phil F
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