Rib overkill

[Sarah Fox]

Hi all,

Dumb question:

In a rib-crowned soundboard, the spring action is in the rib.  However, ribs
are made of wood, and wood eventually loses shape under constant pressure.
There have been experiments with steel soundboards, which don't quite sound
right in the treble end.  But what about spring steel ribs of some sort?
Perhaps thin wooden ribs with steel leaf springs screwed to them, affixed
with a flexible adhesive to prevent buzzing.  They wouldn't lose their
shape, for the most part, and could be engineered to whatever spring
constant is desired.

A related dumb question:

When the treble needs stiffening (higher acoustic impedance and lower
compliance), that would be achieved by raising the spring constant.  Why not
do that with coil assist springs between a frame element and the underside
of the SB beneath the bridge?  An added benefit would be the offloading of
downbearing pressure that otherwise distorts the crown over time.  (The same
downbearing is preserved between the string and bridge, insuring the same
efficacy of vibrational coupling.)

Has anyone tried anything like this?

Peace,
Sarah

----- Original Message -----
From: "Mike Bratcher" <MBratPianos@indy.rr.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: Monday, July 28, 2003 12:31 AM
Subject: Re: Rib overkill


> Ya' know...I had this same idea years ago.  The idea was based on the
> violin.  The panels are made of different woods to cater to different
> characteristics.  Maple for stiffness and good high end tones, and spruce
> for bass tones.  I thought about this in relation to the piano.  Maple is
a
> tougher wood than spruce.  The top panel made of maple could hold crown
> better (maybe), and give better high end sustain.  While the lower panel,
> made of spruce and crowned downward,  could be thinner and give better
bass
> response.  Connect these with a tone pole and you have a pianolin.
>
> Would it work?  Who knows...?
>
> Just a crazy idea I had to use up more wood and drive rebuilders crazy,
not
> that they need any help.
>
> Mike Bratcher
> ----- Original Message -----
> From: "Joe And Penny Goss" <imatunr@srvinet.com>
> To: "Pianotech" <pianotech@ptg.org>
> Sent: Sunday, July 27, 2003 8:48 PM
> Subject: Re: Rib overkill
>
>
> > ??
> > 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
> > >
> > > _______________________________________________
> > > pianotech list info: https://www.moypiano.com/resources/#archives
> >
> > _______________________________________________
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>
> _______________________________________________
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