I'm not going to second guess Ric's calculations. I'm not that smart. But something's got to be changing the pitch on pianos between seasons. If it isn't the soundboard going up and down, and I have trouble accepting the concept of the string riding up on the bridge having an effect on tuning, there is only one other factor that could be the culprit, and that is the plate expanding or contracting. If you think about it, where is the greatest change in pitch? I find the biggest change is at the first couple of notes on the treble bridge. On most pianos, that is the longest distance from one end of the plate to the other. If the plate expands from top to bottom, (or front to back on a grand), it wouldn't take much to change the pitch even a few cents. The reason the bass strings, and especially the lowest few, don't change much is because of the big bass strut, which gives the plate more stability. So perhaps the reason the piano goes out of tune with humidity and temperature has almost nothing to do with the soundboard/bridge moving up and down, but is primarily because the plate is expanding and shrinking. Someone else mentioned something along this line, but it seems have been lost in the conversations. Has anyone done an experiment or taken measurements of this? Wim -----Original Message----- From: William Monroe <bill at a440piano.net> To: pianotech at ptg.org Sent: Sat, Apr 3, 2010 7:59 am Subject: Re: [pianotech] Pitch Change (was: Grey market pianos, seasoned pianos, etc.) Hi Gerald, List, Having sifted through the archives......... ;-] OK, so my memory did serve. Here's an excerpt from Ric Brekne's posting of the math that shows resultant pitch changes due to rise & fall of a soundboard. This shows minimal effect on pitch due to soundboard deflection. Here's a link to the archives as well with the thread, " Soundboard Deflection and Pitch Change / was Downbearing." https://www.moypiano.com/ptg/pianotech.php/2006-August/thread.html#194422 William R. Monroe Ric wrote: .............Let me illustrate..given the following, and by all means check my figurings... (for the moment disregard the width of the bridge and deal in simple triangle trig) - an undeflected string tension of 160 lbs. - string diameter of 0,8 mm. - front length of 50 mm. - back length of 25 mm. This yields a front length frequency of roughly 4248.88 Hz. f = SQRT((T 398 *10^6)/(L^2d^2)) If you then deflect this string 1 mm upwards you get a string deflection angle of a whopping 3.46 ¤, a downwards force of 9.59 lbs, and a frequency of 4248.98 hz. Thats only a change of 0.106 hz.... at note 88 or there abouts. Even a 2 mm deflection would'nt increase the frequency of the string more then 0.42 hz and that would at the same time cause a string deflection angle of 6.87 ¤ !! and a downbearing force of just over 19 lbs... for just one string ! You'd be quickly over 3000 lbs of total downbearing force on the soundboard... If these figures are correct... then clearly soundboard deflection can nearly be ignored when it comes to pitch changes. On Sat, Apr 3, 2010 at 9:55 AM, Ron Nossaman <rnossaman at cox.net> wrote: Gerald Groot wrote: I have read what has already been written in this thread, currently. Ron, I'm not going to sift through the archives. The dissusion has been and still is being presented now. I'm merely adding to it as you are giving my current thoughts on the matter again, as you are. Have YOU had the time to do all of these measurements yourself? If so, I don't know how you managed to find it let alone have the patience for it. I haven't nor do I have the desire to do so. Taking measurements is not the only proof available. When does logic and common sense ever come into play here? It comes into play immediately when you find how much a soundboard has to move to produce the required tension changes. Yes, I've taken a whole lot of time trying to learn how things actually work, rather than assuming that what I was taught was correct. It used to be common sense that horse hairs in the rain barrel turned into worms. I take the time because I'm interested in learning something real. Ron N -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100403/a1c8ab87/attachment.htm>
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