And so, we have arrived once again at one of the list's most common but often unstated points of tension (no pun intended) and contention: hysteresis. The basic question is: • Is the strung piano a deterministic system, where any change is effected immediately and totally, creating a new and stable balance of forces? or • Is the strung piano a system with hysteresis, in which changes that have happened in the past continue to act upon the system in the present, and will continue to act upon the system in the future, thwarting the ability to create a stable balance of forces in the present? Now, at a certain level, most of us probably agree that the strung piano as a whole is a system with hysteresis. Otherwise, pianos wouldn't go out of tune, and our collective burger-flipping skills would be several orders of magnitude higher. So, really, the relevant question is: which parts or systems within the strung piano are stable when changes are introduced, and which parts react to changes over time? Where is that hysteresis located? --- In my opinion, this question is relevant to other points of discussion on this list, including reasons for pitch drop after stringing (string stretch or bend tightening?), soundboard crown/crown changes, seasonal pitch changes, etc. But that's off topic, so let's stick to the "PR follow up" thread at hand. PRJ as asserted that "string segmentation tension differentials" are an area that creates instability over time. Most list participants probably accept that insufficient tension equalization during tuning (leaving drastically less or more tension in the non-speaking lengths of the string as compared to the speaking length) creates a system in which hysteresis will thwart tuning stability. However, most list participants probably also agree that the skill of the tuner in "settling the string" is helpful in mitigating this problem, probably in direct proportion to the tuner's skill. So, I think that we can somewhat leave this point as an area of relative agreement - we all probably agree that a very poor tuner does little or no string settling, leaving an unstable tuning, while a fabulous tuner does an excellent job of string settling, leaving a stable tuning. This is true of any tuning, but the difference in skill will show up much more in a larger pitch raise. Hysteresis is present but controllable. PRJ is also asserting that soundboard compression (and presumably crown) change over time after downbearing forces have been changed via tuning. I am certainly not a wood technologist or an engineer, but, like David Love, I don't believe it. In the little wood testing research that I am aware of, I haven't seen a study in which wood elastically deflects at some point of time considerably after the force bearing upon it has changed, unless it is loaded to near its failure point (which a soundboard should not be), causing plastic deformation. The very few demonstrations that I have seen or read about in the past show elastic deformation of the wood happening at nearly the same time as the change in loading. (quick examples for any unfamiliar with terms: elastic deformation is a recoverable change, for instance bending a wire just a little so that it springs back to its original state when released, whereas plastic deformation is a permanent rearrangement of the material, for instance putting a bend in a piece of wire that stays bent after you let go) PRJ, if you can give any relevant examples of hysteresis in elastic wood loading, other than loading to near the point of failure (causing plastic deformation), I would like to know about them. Changes over a few seconds or even minutes would be irrelevant, because the tuner would account for them in doing multiple passes. However, changes over many hours, or days, weeks or months would be quite relevant. Changes over years would not be so relevant, since we all agree that pianos go out of tune during longer timeframes. Since PRJ is asserting that science shows that he is right and that others are wrong, I think that the burden of proof is upon him to identify exactly how. However, engineers and scientists are most welcome to chime in as well. I do not mean this last paragraph to be confrontational; I would love to be genuinely proven wrong, because then I would learn something important, and our collective understanding of pianos would be raised. Joe DeFazio Pittsburgh On Aug 28, 2009, at 8:49 PM, pianotech-request at ptg.org wrote: > > From: "David Love" <davidlovepianos at comcast.net> > Date: August 28, 2009 8:48:30 PM EDT > To: <pianotech at ptg.org> > Subject: Re: [pianotech] PR follow up > Reply-To: pianotech at ptg.org > > > I don’t see soundboard compression being a factor or that there is > any delay in response to added tension. String segmentation tension > differentials I’ll agree are a factor but those can be overcome with > proper technique and attention—I don’t think they offer a reason > that the piano can’t achieve stability. > > David Love > www.davidlovepianos.com > > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] > On Behalf Of PAULREVENKOJONES at aol.com > Sent: Friday, August 28, 2009 5:02 PM > To: pianotech at ptg.org > Subject: Re: [pianotech] PR follow up > > The most general phrases that seems appropriate to start the > discussion would be soundboard (de- and re-)compression over both > bridges, and the string segmentation tension differentials. Seems > enough. :-) > > Cheers, > > P > > In a message dated 8/28/2009 6:36:33 P.M. Central Daylight Time, davidlovepianos at comcast.net > writes: > Please explain the physics as you know it that would account for this. > -------------- next part -------------- An HTML attachment was scrubbed... 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