I too have noticed this exact pattern both on grands and uprights. I too have been perplexed as to the fact that the string length pattern is reversed from grand to upright. Logic then dictates that it cannot be SPECIFICALLY related to string length (though there may be some influence there). We must look elsewhere.
So, after much deliberation on the matter I have developed a theory. No, I cannot prove it. It is based strictly on observation and logic. Feel free to contradict it, laugh at it, completely dismiss it, argue about it...or perhaps accept it as a realistic possibility.
I believe the phenomenon is the result of an extremely complex interaction between the coupled bridge and soundboard movement, relative to the grain direction of the board, the degree of positive crown, and the relative ability of the ribs to support that crown (i.e. the degree of flex or caving in of the ribs under the bridge with extra pressure exerted with a humidity increase...and vice versa) with a significant enough change in humidity.
In the case of a grand first, assuming that the bridge notching is consistently parallel to the capo bar or agraffes (as the design may be) we are looking for something happening that would result in the middle and right strings (treble primarily) of each unison to all tighten and increase tension (and pitch) relative to the left string (in general). What might accomplish this? Due to the curvature of the bridge, increased pressure in the middle of the bridge (especially with front bearing) would cause the treble end of the bridge to go up (slightly, but it doesn't take much to make a change in tension). Coupled with the the positioning of the bridge relative to the wrasten vs. rim (there is much more soundboard behind the bridge than in front of it), coupled with the relative grain structure/width/angle, and considering the fact the notches put the middle and right strings closer to the center of the bridge than the left string is, meaning that If the bridge is going "up" (and tilting is also happening) then there is more rise in the center of the bridge relative to the edge of the bridge, thus causing this phenomenon.
Now I do believe there is more going on here also with the crown and grain orientation, but I can't put my finger on it precisely.
Now in the vertical, we have essentially a "mirror image" with the bridge flipped over, grain structure flipped 90°, bridge notching correspondingly reversed but the forces would be the same with a humidity change.
If the theory is correct it should have the same effect on the speaking length of the strings as on the grand, causing the right and middle to rise more than the left.
We all remember Steinway's and Baldwin's non-parallel bridge notching attempts on some models, perhaps in an effort to mitigate some of this unison drift effect. That decision would make sense if this theory is correct.
As I said, I cannot prove this, and I think it is a very complicated set of interactions, the degree of which is relative to the specifics of crown, flex, grain orientation, and actual downbearing (where and how much). Too complicated experimentally measure.
Well, that's my story and I'm sticking to to it (till someone comes up with a better one). Have fun with it.
Pwg
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Peter Grey
Stratham NH
603-686-2395
pianodoctor57@gmail.com------------------------------
Original Message:
Sent: 03-17-2018 12:26
From: Jim Ialeggio
Subject: Sharp/flat
Re; the front segment differences mentioned in the thread Alan referenced, and re Susan's comment...ie, if front segments set up different amounts of elasticity, why does the reverse pin/front segment length on an upright behave with the right string going sharp too?
Front segment length is an obvious difference between strings of the unison, and it seems to me to be the most obvious culprit in something like this. What was not mentioned in Fred's observation is : 1-the relative difference between how uprights render in the top section and how 20yr plus grands, especially Steinways, often render in that section. 2-the relative length, and thus elasticity differences, between grand and upright front segments.
Movement under some grand top section capos can be very opaque. If the three strings under the capo do not move in a way that allows one to read them well, the apparent "set" front segment tension has the potential to greatly exaggerate the effect of the unequal elasticity of the front segments lengths. In these capos, the friction can be such, that a functionally stable setting of the string, ie an apparently equalized front segment tension, will not disclose the length induced elasticity differences in the 3 strings front segment, because of high friction...that is, they can be stable until a temperature induced event overcomes the friction. The longer the high friction front segment, the more the undisclosed charge can be to that string segment.
Uprights generally don't behave as badly as grand top capo sections, in the friction department...even beat BOU's with corroded strings. The front segments up there are generally much shorter to boot, so the "un-read" charge remaining in that front segment may be much closer to equilibrium and more transparent to read correctly, relative to the high friction grand. The front segment tension band of the right upright high treble string, has a very small tension band compared to the left string, as its mostly right on top of the pressure bar. The longer segment, in this more transparent friction set-up, would tend to leave the longer front segments closer to the bottom of the equilibrium point, relative to the short front segment right string, which would tend to be closer to the top of the equilibrium point.
Front segments and termination conditions, in grands vs uprights, create more of an apples to oranges comparison, rather than apples to apples, in this regard…I would think.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
Original Message:
Sent: 03-17-2018 08:54
From: Thomas Black
Subject: Sharp/flat
Thanks Ed. What I thought was a weird Steinway D is normal in extreme humid conditions. Now I understand!
Sent from my iPhone
Original Message------
Two things-
1)This is caused by relative humidity change, not temperature. Temperature alone would cause all strings to rise or fall in pitch together.
The DamppChaser web site has a fine teaching and certification program about humidity and wood. Free.
2) I don't recall that Ron Nossaman ever said this did not happen.
As to exactly what in the piano structure causes this, I don't think we have reached a clear conclusion.
With small humidity changes back and forth, my piano retunes itself.
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Ed Sutton
ed440@me.com
(980) 254-7413
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