Dale, The reverse crowned board with downward bearing is an interesting idea. If you installed the crowned board into the piano without ending up with compression preload then the downbearing should preload the board in tension to approximately the same degree as it would preload the board in compression in the more usual arrangement. As I see it the purpose of the crowning and preload due to downbearing is to stiffen the soundboard system without adding mass (as you could do say by thickening the board or adding heavier ribs). Where you need this is at the top end, hence the substantial downbearing at the top end, with almost none at the bottom end of the scale. It would seem to me that the stiffening due to crowning or arching the board would be the same whether it were crowned up or down. It also seems to me that it wouldn't matter whether the stiffening from the downbearing preload were a tension or compression preload. It also seems that you would get the added benefit that as the board tended to take on any set from the preload with the reverse crown arrangement the set would tend to give the board more crown rather than flatten it out as in the more usual arrangement. What would concern me is that wood tends to have much less tension strength than compression strength across the grain and would therefore crack or take on permanent set more readily with a tension preload than with a compression preload. However, wood has much more tension strength than compression strength along the grain and perhaps this would help. It's interesting that on the reverse crowned boards you have seen you haven't noticed deterioration due to the tension preload. Phil --- Phillip Ford Piano Service & Restoration 1777 Yosemite Ave - 215 San Francisco, CA 94124 On Sun, 18 Nov 2001 06:48:16 DALE ERWIN wrote: >Tom and list > > You know I have been following this thread and it is interesting to me how many makers tried out this idea. I rebuilt a George Steck 6 ft. grand last year with this arrangement. When I first encountered the piano the sound was absolutely magic. The sustain just floated for what seemed like forever . The more interesting thing was that the board was a reverse crowned board with a positive set downbearing. I mean bearing set pressing in the usual direction. > A bit more time consuming to string but what a gem. I keep finding all kinds of sound board conditions and configurations which aren't supposed to work that do and others that should that don't! > I have to figure that the weight of the Big Brass agraffes also contributed to the impedance properties of the board probably a sustain enhancing dynamic. > > Ain't life interestin---Dale Erwin----- -----
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