<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> Hi Mark. Yes.. I'd say that was a lot of negative deflection.  I'd also have less trouble understanding how that was possible, at least on the surface of it, then very much more positive deflection then a couple mm on average.  At some point... tho I will be the first to say I am unsure where that point is,  a soundboard assembly will not be able to over come the bearing tension placed on it by the string plane... that much I think we can all be in agreement on. The whole point of the exercise of figuring how much bearing strain is caused for a given change in deflection is simply to shed light on how much vertical force is required of the soundboard for that change.  Those of you who know just how much a soundboard can push (or pull) can perhaps chime in on where things become less then realistic :) For my part... it seems to me like there must be more twisting and turning going on that effectively changes string segment lengths then we generally think. If I get some time later on tonite... I throw out some bearing numbers that result from a 5 mm change in deflection from an assumed 0 deflection starting point for three or four different string lengths. Cheers and thanks for the interesting post... I agree that there has to be significant vertical movement going on... its just that it seems like there has to be a limit to how much the soundboard can move vertically, and it looks to me like the pitch changes we see require quite a bit more then what that limit allows for. RicB <blockquote> Ric, and all I have a Baldwin L awaiting stringing, where the bridges have dropped so far, that a bearing string stretched from hitch-pin to agraffe will not touch the top of the bridge-pins, never mind the bridges! We're talking 5mm - 6mm negative.... how's that for deflection? Last summer, when the piano was torn down for re-string prep, bridge re-pinning, notching, etc. the bearing was positive. And this is not the only piano I've witnessed this on. Last November, on another instrument, several of us noticed the low-tenor strings resting on the plate, on their way "down" to reach the tenor bridge. This bridge was "positive" in August. Our shop falls into single-digit RH in winter, nonetheless, it's not uncommon to see this kind of movement on instruments w/o Dampp-Chaser systems, to the point one feels the bridges are actually and barely being held "up" by the strings. BTW, none of these boards have cracks, and they seem to return to positive bearing, once moisture content is restored. So, in my experience anyhow, there is "plenty" of deflection going on. I have to work with "simple ideas" :>), so I'm still stuck on soundboard movement in response to changing RH,  governed by the varying elasticity of strings across the scale, as the most obvious cause of pitch change. In winter, I witness a common curve beginning with anywhere from 30cts flat at the lowest plain wire note, dropping incrementally up the scale, and leveling-off at about 5cts flat by A4, or so. In the summer I see a vrtual reverse, again, in a very smooth curve, dropping typically from about 30cts sharp, a cent or two at a time, towards the middle. And yes, there is usually a "spike" at the breaks, in some pianos more than others. So, as enticing as the study of wire stretch, bridge-compression, etc. are, I have a hard time "imagining" these factors reversing with such an equal and opposite reaction as my seasonal pitch readings indicate. A soundboard you can spring up or down, and it will spring back, there's lots of elasticity there. And as witnessed in our shop, those things really do move up and down with the seasons. best regards, Mark Cramer, Brandon University </blockquote> <div class="moz-signature"> </div> </body> </html>