Why do we need crown?

[william ballard]

On Apr 23, 2006, at 7:54 AM, Ric Brekne wrote:
> I dont think one actually does need crown.

That could be true, given the number of ways to efficiently couple to  
the strings to the "bridge", which have already been suggested in  
this thread. However that would  ignore the wonderful elasticity of  
spruce, which would seem a shame. I mean, the string plane is  
elastic, so why couple it to an inert diaphragm? (Well not completely  
inert, but at the small  excursions the string plane normal subject a  
board panel to, a flat board wouldn't get too badly "bent out of  
shape". Thus, its elasticity would hardly get woken up.)

> Del seems to think that crown was an accident to begin with, and  
> tho I am not sure I would go that far...

Del does make a good point. If t were the idea of an engineer or of a  
factory's R&D department, there would be a patent on it (plus  
accompanying sales hoopla) in the historical record. Del has found none.

I'd go along with Del, that it was an inadvertency, the by-product of  
large assembly and hide glue. It became accepted by testing the  
converse, waiting unto a rib-glued board had fully returned to  
ambient EMC, then trimming the excess so it would once again fit  
inside the rim.

> it seems to me that all you need is adequate downbearing support   
> and a good combination of mass and stiffness.

Seems to me that the only reason we're worrying about adequate  
downbearing support against the string load or a board panel which is  
flat to begin with, is the fear that the downbearing of the strings  
(being borne up into by the bridge height) would push the panel  
through flat into a negative crown. But wouldn't the string plane  
only push the board until the string plane itself flattened out?.

I'm guessing that negative crown with negative bearing would produce  
the same pair of opposing springs (board panel plus string plane)  
that we all grew up calling home, with positive crown and positive  
downbearing. You'd enjoy the same mechanical advantage either way.  
(You'd just have to toss out bridge pins as a coupling mechanism.)

On Apr 23, 2006, at 11:15 AM, Ron Nossaman wrote:
> Then you'd have a no crown no bearing piano that works, but still  
> sounds somewhat different than we're used to, which isn't  
> necessarily bad.

"Ladies and Gentlemen, over in this corner, wearing the purple  
shorts, we have...." a no crown no bearing piano that works, but  
still sounds somewhat different than we're used to, which isn't  
necessarily bad........

.........but not something I'd bet on when it goes up against  the  
reigning champ, a crowned board ("Spring'o'Spruce™") with appropriate  
bearing.

BTW, many thanks to the Boston Chapter for its one-day session with  
Del yesterday. Can you tell, instantly I'm an expert with opinions.

Mr. Bill

"No one builds the *perfect* piano, you can only remove the obstacles  
to that perfection during the building."
     ...........LaRoy Edwards, Yamaha International Corp
+++++++++++++++++++++