Unusual rib structure?

[Ron Nossaman]

>OK, there's something about my piano (1933 Wissner 9') that seems odd (in 
>my limited experience), and I've just got to ask.  My soundboard ribs have 
>an unusual structure (I think), and I'm uncertain as to the purpose.  Most 
>of the ribs are "tied" together with one of two small cross-braces.

Hi Sarah,
This is done where there should be a cutoff bar, but isn't, like the 
Steinway B shown here 
[link redacted at request of site owner - Jul 25, 2015]
I understand it, when the soundboard gets too big (as they most all are), 
and the ribs too long, the board breaks up into too many competing 
vibrational modes and resonances and fights itself. The small bar 
connecting rib bottoms stiffens critical areas and helps minimize the 
formation of these counterproductive modes. It also stifles some necessary 
soundboard movement, so the ribs are thinned where the bar attaches to try 
to get back some, but not all of what the bar eliminated. It's a fix of the 
fix. The second step level is the regular feathering. Putting in a real 
cutoff bar instead would have been a better approach, but would have 
lowered the number of square inches of active soundboard area, which 
wouldn't have looked good in the brochure. I don't know why they did it in 
the tail too.


>Was it a way of bracing the crown, which is quite a lovely one.

Measured where?

Ron N