Soundboard Stiffness, was: (no subject)

[Farrell]

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Hello Gene Nelson. You will find a better chance of someone responding =
to your post if you use an appropriate subject line (many will just =
delete no subject). And it is nice to sign your posts.

I will intersperse a few thoughts I have on your questions. I don't =
think I really have any answers for you, as so much of this is still a =
bit nebulous to me also. But maybe together we can bug someone =
knowledgeable into responding!

Terry Farrell
 =20
----- Original Message -----=20
From: "Nelson. Gene (PWA)" <nelsong@SacCounty.NET>
To: <pianotech@ptg.org>
Sent: Sunday, January 19, 2003 1:43 AM
Subject: (no subject)


> Please help a newbee understand.=20
>=20
> I am trying to picture where the stiffness is in soundboards. If you
> consider the typical compression type that has ribs and board pressed =
into a
> caul, then the ribs are pulling the board toward the flat side or the
> position that the ribs want to come to rest. Is this creating =
stiffness in
> the soundboard?

The ribs are trying to flatten out, but the panel will only compress so =
much, so you end up with some crown. So I think your question is: is =
compression-generated crown responsible for soundboard stiffness. Good =
question. Or is the stiffness simply a characteristic of the material =
properties and dimensions. (My gut tells me the crown will add to the =
stiffness, but I know what I am picturing is the dome-and-buttress thing =
which does not appropriately apply.)
=20
> The reason I ask is that recently I had a chance to be instructed on =
how to
> handle a new soundboard out of the box without ribs attached. It =
quickly
> bacame obvious how fragile they are in this state. Any mishandling =
could
> easily cause a fracture. Then I think about the grain orientation and =
how
> the bridges are aligned to this with exception of the extreme treble =
and
> maybe some of the bass. Along the grain is the weakest part of the =
board -
> am I wrong? So where is the stiffness.=20

I have noted the same thing. The unribbed panel can be like a wet =
noodle. But only ACROSS the grain (perpendicular to the grain or long =
axis of the tree). The panel has a fair bit of stiffness along the =
grain. The long bridge will add to the along-grain stiffness. After ribs =
are glued to panel more-or-less across the grain, the soundboard will =
have stiffness both along and across the grain.
=20
> Also curious, is board stiffness something that can be calculated?

No doubt! Del?

> Is it a factor in rib design?

I'm sure overall stiffness is going to be the combination of the =
physical properties of the panel, bridge and rib (and maybe the shape, =
as in crown?).

> Is it used to calculate how bearing is supported?=20

I suspect the answer is that is should be. I'll bet there are many =
factory sad/horror stories related to this not being taken into account?

> Or is board stiffness related only to musical qualities?=20

Another I don't know the answer to. I suspect it will also relate to =
soundboard longevity.
=20
> Thank you very much.

And thank you for posting some interesting questions. Let's hope some =
knowledgeable soul can shed some light here.
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