Time for a change of subject heading, I think : At 16:43 -0600 23/1/08, Ron Nossaman wrote: >I said Steinway US, as in NY. They have always used flat ribs, and >by all indication always will. The Hamburg product is considerably >different. An eternal source of confusion also comes from the always >vague wording concerning "curved" ribs. If the curve is cut into the >rib, yes, it's rib crowned. If the curve is bent into the rib, no, >it's compression crowned. Which is the case here? I don't know how you would "bend a curve" into a rib except by steaming it and thus straining the structure and I can't imagine anyone going about it that way, so I have little doubt that Hamburgs ribs are planed to a crown just as most people's if Hartwig is to be taken at his word. >>>..and supplying positive beam support to crown under downbearing >>>in addition to the support supplied by panel compression. >> >>This compression being created by the force produced by the summer >>growth (mainly) of the spruce trying to expand after being glued to >>the ribs in a more or less dehydrated condition. Is that what >>you're saying? It seems to be, but anyone reading your description >>without much knowledge might easily ask "what compression?!" > >Yes. Panel compression is also commonly achieved or increased by >pressing the assembly into a curved caul as the ribs are glued on. Well, that is not the compression that is most significant! The dished table is just a device to facilitate close contact of the ribs with the board while gluing. Of course some compression of the fibres will result at the dished side but at the same time some tension, or stretching of the fibres, will result on the under-side. The significant and more telling compression results as the board re-hydrates, at which time the temporary tension introduced by the slight bending is negated and quickly changed into compression, which compression is further increased as the down-bearing of the strings comes into effect. Now to use the local neologism of "rib-crowned" for such an assembly, no matter how it may have caught on, strikes me as either misleading or just plain meaningless. The term suggests that the board is crowned by the ribs, which is not the case at all, and the contrasting of "RC" with "CC" leads one to suppose that compression is not present in a "rib-crowned" board, when in fact compression is the principal factor in the development and maintenance of the crown and the crowning of the ribs is carried out simply to prevent the ribs from straining to pull down the naturally-formed crown to no purpose. >Yes. My crowned rib sets would support full string downbearing >without the panel being present. How would they sound? :-) >I dry panels to 6%MC, so depending on where the piano goes, there >will often be some compression in the panel. The difference is that >the RC&S assembly doesn't need panel compression to maintain >stiffness and crown under bearing load, where the CC and RC do. I understand. Now, while my own personal hobby-horse is that all that matters in a soundboard is the ratio of stiffness to mass; given the very imperfect aeolotropic nature of spruce and other woods and the need to make it behave and provide as much stiffness or resilience as possible across the grain, compression strikes me, and has struck countless others down the generations, as a very useful aid. Terry Farrell mentioned recently the behaviour of a certain make of piano whose soundboard has neither crown nor compression: At 06:51 -0500 26/11/07, Farrell wrote: >Have you ever listened to a Xxx? Maybe some would want to call what >they have "power", but the pianos distort badly at any medium-lound >volume. My answer to that is first: yes, I have, at the inauguration of one of them at a hall in Wales. My first impression during the concert was that it sounded rather like a very old Bechstein, and a friend oan colleague who was with me agreed. Afterwards we went on stage and I was invited by the maker to try the piano. After playing it sensitively for a few moments I decided to test the impression I had that it would break down under heavy playing and hit it for all it was worth. The effect was catastrophic. I might as well have kicked a pile of tin cans. That is not to say that either compression or crown are necessary for a good soundboard -- but for a board without either, spruce is not the right stuff. JD
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