[pianotech] Reversing Crown

[Ron Nossaman]

Noah Frere wrote:
> I find this confusing because I would have assumed that as soon as the 
> soundboard starts pulling away from the strings, and negative bearing 
> sets in, then the strings would be /pushing/ the soundboard down 
> further, rather than pulling up. 

I don't see how. Positive bearing is what supplies down 
pressure. Negative bearing would pull up. The string is under 
tension and trying to maintain a straight line between capo 
and aliquot (or whatever).


>I imagine it this way: imagine a 
> tunpperware container with a lid that's slightly convex - you push the 
> sides together and it forces the lid up higher. (the equivalent of 
> putting on strings). 

No. Putting on strings, assuming positive bearing, will push 
the board down, not raise it up, and the rim has nothing to do 
with it.


>Now take the pressure off the container and push 
> the lid down just enough to make it concave, reapply pressure, and the 
> lid will continue its downward path.

Again, you're manipulating the perimeter, which in a piano 
would be the rim. The rim has virtually nothing to do with 
crown formation or support in a piano.


>    Visually this description reminds us of the soundboard, but i mean to 
> apply it to downbearing. 

Then where is the downbearing in your illustration? There is none.


>That is, no matter which direction the crown is 
> facing, the tupperware lid represents the board/bridges as a whole. 
>    However, being neither a physicist nor a rebuilder, i must have it wrong,

Yes, wrong. <G>
Ron N