Ron writes: << Soundboard crown still isn't supported like a buttressed arch, Ed, and rim or belly rail spreading the few thousandth's difference between the length dimension measured straight from rib end to rib end, and that measured from rib end to rib end over the crown won't make the crown go flat. It just won't.<< I know that someone has done the math on this. How much "spread" is required of a rib that is 20 inches long, curved on a radius of say 40' to allow the center to drop .020"??? It has been too long since I dragged my kids through high school geometry to remember arc and such, but I know somebody out there has the answer at hand. >>Flexibility in the belly rail and rim will certainly damp the soundboard and affect tone production adversely, but the crown is formed and supported by rib and panel, independent of the rim. >> There is evidence for debate on the arch theory. The observed change in the Mason & Hamilin centripedal resonator when the strings are removed. In every case I have seen, (more than several), destringing a Mason changes the tension on the bars, ( judged by rattles that appear when destrung). Perhaps the strongest indication I know of that the arched board attempts to spread the case is the Chickering grands with the inner rim. All of these pianos,(I have had 4 of them), when destrung, show the inner rim to come inwards. A wedge that is very lightly placed between the inner and outer rim before stringing will be extremely tight when the strings are pulled up to pitch and the screws that pass from inner to outer around the perimeter will also be looser. There is definitely outward movement of the relatively flexible inner rim under downbearing pressure. If the board simply presses downward on the shelf, this particular construction, with its cantilevered support, would bend inwards, no? These Chickerings also have really nice sound with virtually no bearing, even though without any strings on them, there is a boatload of bearing They simply flatten out and I have, in the past, attempted to add bearing by lowering nosebolts,but the board just keeps on flattening out as I do. The unsupported span of the belly rail on grands often has a slight curve outwards between the horn and their attachment to the treble case side. I don't think this was built into the pianos originally, so what other force but soundboard spread would do this? Ed Foote RPT www.uk-piano.org/edfoote/ www.uk-piano.org/edfoote/well_tempered_piano.html
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