I have been following the pitch-change-due-to-belly swelling thread with some interest and would like to add the following. First of all, the scientific method holds many requirements. High on that list (philosophically anyway) is the idea that observed physical phenomena (OP) require satisfactory scientific explanations. These explanations usually exist in forms of mathematical equations; and these formerly derived through incessant testing and verification followed by agreement and consensus of those not only behind the slide rule, but by those whose still sharp human senses have not been dulled through distrust. Per our subject at hand: if there is no consensus among piano techs and players that pianos go sharp during seasons of higher (relatively) humidity, then the subject is DOA. The consensus does exist in large numbers, however, and strongly held ------ that our senses and experiences suggest that belly wood swelling causes a sharpening of pitch. At this point no mathematical verification seems required as intuition and sensation appear fitting. When a formal (i.e., scientific) verification is required, it must uphold the OP and not defeat the OP or else the OP, regardless of consensus, is flawed. If the outcome of a particular mathematical approach fails to support the OP, then another approach, followed by another is required until the scientific explanation succeeds in supporting the OP. Now, this may seem too obvious as to be not worth stating; but I think it is worth a reminder. A common pitfall (quite common in all schools of learning and even in everyday life by the brightest minds) occurs in not trusting, or at least factoring in, our own senses. Worse is the tendency to try one formal approach, and when this approach fails to suggest the reason for the OP, to now draw conclusions that that initial formal search regarding “xyz” is final, and that what ever else is going on, we have clearly eliminated “xyz” as a possible cause. RE the hypothesis that pitch change due to the rise and fall of the belly system is suspect, followed by a conclusion that soundboard deflection due to ambient swelling is an insignificant cause of pitch change needs to be challenged, either in part or in full. I say this because recent posts on the subject (and many well thought out) suggest some unnecessary confusion. I agree with Frank Emerson that RicB’s contribution to the subject is not completely clear, and that perhaps we could persuade Ric to resubmit, and / or rethink his position on this. For one thing, I would like to know what others think of the downbearing calculation of 9.59 lbs increase due to a 1 mm addition to “bridge height”, and what this increased force has to do with the stated minimally increased tension / frequency. I hope to follow up on this at a later date. Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 _____ From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Gerald Groot Sent: Saturday, April 03, 2010 4:33 PM To: pianotech at ptg.org Subject: Re: [pianotech] Pitch Change (was: Grey market pianos,seasoned pianos, etc.) I did read that William, thank you. After reading more of it as well, it appears to me that there is much more speculation than positive proof either way from either Ric or John. I visited with Dr. Yat Lam Hong all afternoon today. He is a man FULL of information and is most willing to share it. How he manages to retain it all is beyond me. I wish I had that kind of memory. For those of you that do not know Yat Lam, he is an extremely knowledgeable RPT. I asked Yat Lam Hong his philosophy on what he thought was the main cause of why pianos go out of tune so drastically from seasonal changes and his immediate reply was "humidity." He went on to say that "humidity causes swelling and contraction of the sounding board sending pitch up and down.." A pure and simple answer Jer From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of William Monroe Sent: Saturday, April 03, 2010 1:59 PM To: pianotech at ptg.org 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. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100405/29f3c5b8/attachment-0001.htm>
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