Unusual rib structure?

[David Love]

I noticed, the other day, on a Hamburg Steinway C, that the cutoff bar was
notched to allow for the feathered part of the rib to extend beyond it to
the rim.  Is this counterproductive?  Generally, with cutoff bars do the
ribs terminate at the cutoff bar?

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Ron Nossaman <RNossaman@cox.net>
> To: Pianotech <pianotech@ptg.org>
> Date: 5/7/2003 11:27:30 AM
> Subject: Re: Unusual rib structure?
>
>
> >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]
As 
> 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
>
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