John, We the proviso that the superposition of traveling waves develops the standing wave patterns in the soundboard this seems to be pretty much the way I see it too. Regard Robin Hufford John Delacour wrote: > At 11:28 PM +0100 12/16/01, Richard Brekne wrote: > > >John Delacour wrote: > >>....If the solenoid of a speaker is jammed, no sound at all will be > >>emitted from the cone. The two cases are completely different. > > > >Touche'. In otherwords.... the diaphram analogy is far from adequate to fully > >describe all of the sound producing elements of the soundboard ??. > > As another illustration of what I've been saying about the bridge, we > might hark back to the Kundt experiment that you, Richard, drew our > attention to during the Great Compression Wave Debate. > > You will recall that a thick metal rod was clamped firmly at its mid > point and made to vibrate longitudinally by means of a resin-covered > chamois leather pulled along its first half. At the end of the > second half was fixed a disk which fitted quite closely, like a > piston, in a long air-filled glass tube. The compression wave > travelled along the rod and caused the disk to set up a compression > wave in the air whose length could be measured using a scattering of > cork granules, etc. > > The rod is firmly clamped and rigid; it cannot move longitudinally > and yet it can carry a compression wave thoughout its length and > excite vibrations at the same frequency in the disk, to which it is > attached at a right angle, just as the bridge is attached to the > soundboard. The disk creates a compression wave in the air in the > tube by its _transverse_ vibrations, just as our soundboard does. > Thus a compression wave in a static body is converted into more or > less complex transverse vibrations of a flat body, whether the disk > or the soundboard. > > In the case of the bridge/soundboard pair, the bridge is "clamped" > only in so far as it is held firmly in equilibrium between two equal > and opposite forces. The bridge is the locus of the points where > these forces oppose each other and is roughly speaking at a location > where the system is the most flexible, a good distance from the rigid > fixings of the perimeter. The tranverse movements induced in the > board disturb this equilibrium and the whole structure of board, bars > and bridges etc. is set in vibration of a complex nature. > > I'm not handing this out as gospel, but merely as the very simplified > view that I currently have of the way things work, which seems to be > logical. I'd very much appreciate any educated comments on this view > from the more qualified. > > JD
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