Hi Robert and all: back in the late 60's I had occasion to do strobe light studies of string vibration modes. We had a grand action model which could be used to excite the single string of your monochord. With strings terminated over a simulated V-Bar at each end of the speaking length, the string exhibited an elliptical motion which rotated from side to side in planes almost as steep as these: / \ . It was not circular but elliptical. Although I did not do this experiment, I suspect that if we had used a bridge pin type termination with the bridge pin slanting upward to the left, the elliptical would have alternated between | \. If I find time, I may try to duplicate this experiment. For those of you not familiar with strobe lights, some can be varied in speed to match a particular mode of vibration so that it appears that the string is standing still or moving very slowly. Jim Coleman, Sr. On Sun, 13 Apr 1997, Robert Scott wrote: > Jerry Anderson wrote: > > > >A number of years ago I witnessed Rick Baldassin, in a convention > >class, demonstrate that a plucked string emits a different set of > >frequencies according to whether it is plucked in a horizontal > >(in the plane of the strings) or vertical (toward the soundboard) > >direction. > > > >It would seem that the vertical plucking would most approximate > >the principal mode of a string struck by a hammer. > > > Again I must refer to that most excellent article in January 1979 > Scientific American, pg 118, by Gabriel Weinreich. In that article > he details his studies of string motions and their coupling to the > soundboard and to each other. He found by direct measurement > that the initial vertical motion of the string precesses into a > round-and-round motion with both vertical and horizontal components. > This precession affects the decay too. When plotting the decaying > amplitude as a function of time, Weinreich observed that the inital > rate of decay transformed into a somewhat slower rate of decay. He > found that this correlated with the vertical vs. round-and-round motion > of the string. When the string is initially struck, the motion is vertical. > Vertical motion has maximum coupling of energy to the soundboard, > so the amplitude decay rate is set by how fast energy is leaving the > string and going into the soundboard. But when the motion > precesses to round-and-round, half of the energy is in vertical motion > and half is in horizontal motion. The horizontal motion does not > couple to the soundboard nearly as well, so the energy stays in the > string and the decay rate is not as great. > > This is only one of the interesting conclusions of Weinreich's article. > If your library has back issues on microfilm or something, I strongly > recommend taking a look at it. > > Bob Scott > Ann Arbor, Michigan > >
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