Rib overkill

[Joe And Penny Goss]

??
Has anyone ever made a piano with two boards. Parallel to eachother with
different stiffness factors?
Joe Goss
imatunr@srvinet.com
www.mothergoosetools.com
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Sunday, July 27, 2003 7:28 PM
Subject: Re: Rib overkill



> It can. A more flexible board will tend to be generally louder, with
> shorter sustain. A stiffer board will tend to be not as loud, with longer
> sustain.
Will the bass suffer?
>
> Yes. If there is to be any hope of getting a fundamental out of the low
> bass, the board needs to be flexible down there, and the back scale needs
> to be long, and the core wire needs to not be the diameter of an 8d nail.
> At the same time, the treble needs to be stiff or you will get the
> percussive attack and short sustain of the "killer octave" through the
last
> two octaves or so. Stiffness requirements are widely different from one
end
> of the scale to the other.
>
>
> >I think I also remember Del mentioning something about a board giving too
> >much of a percussive sound and not as much string sound.  Is this with a
> >board that is too stiff?
>
> Probably too flexible.
>
>
> >How does the thickness of the board relate to how much load it can
support?
>
> It depends on the crowning method. A compression crowned board will be
> stiffer with a thicker panel, and support comparatively more load than a
> compression crowned board with a thinner panel. With a rib crowned board,
> assuming it is really rib supported and not just a compression crowned
> board with machine crowned ribs, the panel thickness makes much less
> difference. With a rib crowned, rib supported board, there is no need for
a
> thick panel if the rim is solid.
>
>
> >And in relation to the rib thickness?
>
> Again, it depends on the crowning method. Compression crowned boards tend
> to have ribs wider than they are deep, because they start out flat and the

> panel expansion has to bend them to form crown. Rib crowned and supported
> boards will have ribs less wide, and deeper, regardless of panel
thickness.
> Ribs get stiffer in proportion to their width, and to the cube of their
> height (and inversely to the cube of their length), so a little bit of rib
> height makes them a lot stiffer.
>
>
> >I'm sure all these things are interrelated.  What are the trade-offs?
>
> Those are some of them.
>
>
> >Next, I'm sure the size of the board is a factor.  A smaller piano will
> >have more support from the rim, because the there is more rim per area of
> >board.  Yet another factor to consider, aye?
>
> Absolutely. Soundboards, contrary to manufacturers' marketing literature
> bragging about how their soundboards have more area than their
> competitors', are for the most part already too big. Redesigns I do
> typically lose something around 20% of the existing active soundboard
area,
> depending on what I started with.
>
>
> >How does one judge or weigh the trade-offs?  There are so many variables.
>
> A bunch of variables, the most critical of them not the ones we have
always
> been taught were all important. One can either put in a couple of hundred
> soundboards, making incremental-to-major changes in virtually everything
> until he works out a set of priorities and effects of design features, or
> he can do what I did and start rethinking what I thought I knew against
the
> good fundamental science and physics based advice and guidelines of
someone
> who did do the basic R&D from scratch. That would be Del.
>
>
> >There's no real point here to my questions.  I am always trying to learn
> >more about my trade.  And who else do I learn from other than the folks
> >who do this every day?
> >
> >Mike Bratcher
>
> Every day's a new day for all of us isn't it? There's always something to
> learn - and heal up from.
>
> Ron N
>
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