>My conclusion, after all of this, is that vibrating strings--regardless of >what is happening at the molecular level--physically move the bridge they >are attached to. If the bridge is physically attached to a soundboard, then >that soundboard moves in concert with the motion of the bridge. John, Robin, try this with a strung piano. A dial indicator, mounted on as rigid a beam as you have available, spanning from rim top to rim top across the center of the scale. Position the indicator plunger on any unison you like out there in the middle of the soundboard. Place your finger on the strings of a unison in the same area, directly over the hammer, and strike the key as if you were demonstrating the sustain characteristics of one of your pianos to a skeptic. Remember that feel. Now press down on the strings of the unison adjacent to the gage one about the same amount and observe the indicator dial. It will move. That is not a vibrational stress phenomenon requiring conjecture, elaborate analogies, intuition, web sites, quotable authorities, and faith to accept. That is a slow, observable undeniable physical movement of a strung loaded bridge by a deflected string, or strings of one unison, requiring only the most rudimentary grasp of basic mechanics to comprehend. So it only moves 0.0005". It still moves. We have finally ascertained that any movement at all is some movement, and I guarantee it's not a localized vibrational stress phenomenon that doesn't move the rest of the bridge. You are, aren't you, pressing on unison strings other than the unison where the gage is positioned? Nor is 0.0005" anywhere near the molecular level. The bridge obviously measurably moves. Since the bridge moves, the soundboard must move with it. If you assume only one square foot of the soundboard moves that amount, though it should average to a considerably larger area over the entire board, it will displace 0.072 cubic inches of air with that movement. Do that 880 times per second at 440 cycles (displaces up, and down you know), you will move 6.336 cubic inches of air per second just from that average square foot of moving soundboard. I expect that would be audible, even if the rest of the strings weren't moving along with it and adding their mass to the system, which they will be in actual play. Oh, but that's not a fair test because you have to push too hard to get that 0.0005" deflection. Fine. Push less, get less deflection, and produce less air displacement, which would result in less volume from the instrument if the string were then allowed to vibrate from that displacement amplitude. No mystery there I trust. Below a certain minimum point, the string won't be able to move the bridge enough to move the soundboard enough to produce audible sound if it were vibrating instead of being manually deflected, but it will still directly move the bridge. This is not a terribly difficult concept, and this illustration doesn't require sophisticated equipment and obtuse education beyond the reach of the average piano technician. All sorts of compression waves and molecular level stress disturbances can be immediately moving through every part of the bridge from the first movement of the string, but they're clearly not what moves the bridge. The strings move the bridge, the bridge moves the soundboard. Ron N
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