I didn't think that wood expanded and contracted very much along the grain and that crowning took place due to the dimensional changes across the grain. David Love davidlovepianos@comcast.net -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of Richard Brekne Sent: Friday, February 11, 2005 4:54 PM To: Newtonburg Subject: re: Killer Octave & Pitch Raise Udo Steingręber and I got into a conversation about this in Helsinki a couple years back on the only opportunity I've had to sit and chat with him. It was part of a discussion where he was explaining why he felt compression soundboards were the way to go. He mentioned something about the so called K point (I think this is a Klaus Fenner coined term), which as I understood it was that point on the soundboard where crown from both along the grain and cross the grain intersect and is at its highest point. This area is exactly (and always) in the area typically refered to by american techs as the <<killer octave>> area, and of course varies somewhat from piano to piano. It is then also the exact point then that is most vunerable to failures. Udo was of the position that along the grain crowning was every bit as important as cross grain crown. Something to do with along the grain compression due to downbearing having a stablizing effect on cross grain crown and strength. He also meant that both these were needed to produce the kind of acoustical results he wanted from a soundboard. I'm under the impression, correct me if I am wrong, that most of the rib crowned methods extoled on this list do not employ any purposefull along the grain crowning as part of how the panels are attached to the rim, and therefor do not have this vunerablity. It would stand to reason that they too are not able to create the same acoustical results.... (whether that is preferable or not is an entirely different subject). Disclaimer. This description is my understanding of what Udo was saying, tho I beleive it is pretty accurate. Not being a soundboard engineer tho, I'll leave it to more experienced to explain, interpret, or whathave you the above. One other thing tho... I've always heard that large changes in pitch, and destringing / restringing proceedures should be carefull of this area.... making carefull changes that are appliled very evenly, exactly because this area can easily be damaged by sudden large changes in the stresses applied to the panel as a whole. Seems to jive well if the basic view above is correct to begin with. Cheers RicB _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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