Terry I do appreciate having to clarify this because it is a complicated subject I think of all the time and has taken seemingly eons to digest . Good question . The really important underlying "Jist ot the matter" is that uneven pressure creates uneven impedance qualities. Thats Bad. For example and I've expierienced this on many pianos new and old . Certain notes are louder than others or sing longer and these notes are right next to each other. It could also be a group of notes, frequently it is in octave 4 f thru b. One give away sound is kind of a thwacking sound. The quick irritating attack then weak sustain.O.K. can't voice it out either , maybe camoflouge. This is a result of impedance problems caused by loss of crown and or most often (in my opinion speak up my brothers)an non uniform setting of bearing slash string pressure. I.E How do I know this great mystery? Cause I've induced this condition myself on my own newly made boards in my pre nonstressing of the board days . I did fix the condition by resetting the bearing and the anomally went away. It's only my opinion but many new pianos are not set up with enough bearing which has been born out thru restinging and resetting bearing on several makes of asian pianos. Until you do this a few times I can see why "you might be inclined to think that the amount the board is prestressed is a big assumption" but here in lies the proof. When rightly done it sounds wonderful and the fearless bubble gauge will testify a very uniform reading thru the majority of the piano ,has been set . The risidual values as measured will be in the 12 to 15 thous,range or slightly higher or lower.. And higher in the last treble lower in the bottom tenor (cause you made it that way) and then the bass ,oooohh I can't go there now but much less ? The beauty of this system is that it is possible to set up very favorable bearing requirements without being a rocket scientist . And , each board , with practice can kind of tell you how much to pre-load ( That and some good ole folridian common sense. Use of the infamous Kansas staightedge is a very helpful diagnostic tool. Thanks Ron N. By the way you answer this one, how much bearing does a flat board need /get. After all many flat boards(or Worse) are restrung every day in America. One last teaser . The bearing is not really set uniformly at all! There is proportionately more pressure as you leave the tenor and head for the top of the piano even though the gaposis measured at the tenor string rests seem larger . Hey ,but it's designed that way to meet the specific impedance needs of the treble and each of the sections . Also pre-stressing provides for adequate amounts of bearing over the life of the piano and its ever shrinking crown. shrinking crown shrinking bearing. Really it's a very workable system . Consider yourself armed and dangerous! From the west coast chapter of rebuilders anonymous President and founding member Dale Erwin
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