Why do we need crown?

[Ron Nossaman]

>     *But wouldn't the string plane 
>     only push the board until the string plane itself flattened out*?.
> 
>   /_Yes ! Of course_/

No, not really. I've measured both negative crown and negative 
bearing in a lot of killer octaves that still had a bunch of 
bearing in the treble. That third class lever effect I've 
talked about, with the treble end as the minimally deflecting 
fulcrum, can and does lever the killer octave, which is in the 
extreme bend of the bridge, and gets no beam support from down 
scale like it would with a straight bridge, into negative 
bearing and crown.


>     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.)
> 
>   /_Seems right_/

No reason it couldn't work, if it was designed to be that way. 
It's unlikely that you'll find a piano designed for positive 
crown and bearing that will sound good through a full dynamic 
range in this condition.


>     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'Spruceâ„¢") with
>     appropriate 
>     bearing.
> 
>   _Yes I agree.  I once tuned a miserable 9 ft kawai that never really 
> had any fire in the tone .  Then one day, when I had time to kill ,I 
> checked the bearing with a lowell gage .  ZIp, nada nothing.  I used a 
> crown string to look at bearing.. Massive Crown.  No bearing.  Moral of 
> story.  The car looks good but there is no gas in the tank .  The same 
> is true of springy spruce with no bearing.  Looks good but it doesn't go 
> very far._
>   Dale

And I was, of course, talking about something designed and 
built for zero bearing and zero crown throughout, not 
something that was designed for positive bearing and crown and 
badly built.

Ron N