----- Original Message ----- From: <A440A@aol.com> To: <pianotech@ptg.org> Sent: Thursday, April 10, 2003 7:06 PM Subject: Re: Killer Octave Question > 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? Well, there is movement. Though none of this supports the arch theory. The numbers just don't add up. When tension is applied to a set of piano strings a whole lot of things move. Contrary to popular myth piano plates are not completely rigid structures. Neither are piano rims. Both move and twist as something like 35,000 to 40,000 lbs of force are applied to them. Sometimes by quite a lot. Del > 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? It's hard to say where this comes from--I would guess from natural wood movement over the years. I doubt you're going to be able to see the 0.001" or so of distortion that might possibly be contributed by the rib flattening out. Assuming, of course, that the both rim assembly and the rib itself are made of a material that is perfectly non-compressible materials. Del
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