Slanted bridge question

[Ron Nossaman]

>Ron,
>
>We where talking about the reason for the slant in the treble bridge of some
>grand pianos, towards the hitch pin panel i.e; Bösendorfer with a 4 to 8 mm
>slant for 200 mm lenght (according to the specs transmitted by the factory).
>My friend thought this sland is designed push intentionally the sounboard
>(with the pression/ tension of the strings ) in a very small S shape , not
>so important than when the sounboard collapsed because of bridge roll i.e.
>This S shape would allow a more stable shape behind the bridge.
>My personal guess is it have something to do with the downbearing, better
>mechanical rendment, more pressure on the front pins on the bridge, or
>something like that.
>Or would the (curved) bridge be more rigid  with this shape ?
>
>What do you think ?
>
>Thank you
>
>Isaac OLEG
>

Isaac,
I'd say you were right. It's for a more secure string termination on the
front side of the bridge (speaking length of the string). An S curve in a
soundboard will not react as predictably to humidity swings as a balanced
positive crown will, and the board impedance in any given area will be
considerably different on either side of the bridge. I still say that a
conventionally designed board with any S curve in the tenor/treble is a
failed board. That Ovation guitar is an entirely different kind of system
since there is no plate with hitch pins, the soundboard is not crowned, and
the soundboard and bridge are supporting all the string tension and bearing.
Very little of what you see in a guitar or violin applies directly to pianos. 

Beam (bridge) stiffness increases with the width of the bridge, and with the
cube of the height. That small angle at the top, by itself, won't make it
any stiffer. Incidentally, if you have ever had the long bridge out of a
piano, it's kind of surprising (at least it was to me the first time) how
flexible it is. You kind of have the feeling that it will be a lot less
springy than it really proves to be. For what it's worth. 

 Ron