Crown in a new Soundboard

[Ron Nossaman]

> Consider a new soundboard installation in a Baldwin 9' grand piano. This
> new board has not been stressed as yet, i.e. it has not been strung.
> Also, it's still kind of summery in the Ohio Valley, no heating days
> yet, humidity is still up.
> 
> What amount of crown would you expect to see and be able to measure in
> the center of the board ?
> 
> In other words, if a straight edge is laid across the rim and the
> distance between the board and straight edge is say 7" on both ends,
> what measurement would you want or expect to see in the middle of the
> straight edge. Or, a thread stretched along the longest rib from
> underneath, same question.

Why?

It depends on how the board was built. Is it compression crowned 
from flat ribs? Is it rib crowned and panel supported? Is it rib 
crowned and supported? What radius or radii were used if rib crowned?

If the panel was thinned at the edges, measuring from above is 
useless. For the most part, measuring crown in an un-loaded board 
won't tell you much of anything and even then, measuring crown at 
just the longest rib is of very little value. It also won't indicate 
how the piano will sound strung.

Again, why? What do you find, and what are your concerns about what 
you see?

Ron N