Untapered Soundboard Ribs

[Farrell]

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----- Original Message -----=20
From: "Delwin D Fandrich" <pianobuilders@olynet.com>
To: <pianotech@ptg.org>
Sent: Thursday, July 18, 2002 11:15 AM
Subject: Re: Untapered Soundboard Ribs


>=20
> ----- Original Message -----
> From: "Farrell" <mfarrel2@tampabay.rr.com>
> To: <pianotech@ptg.org>
> Sent: July 18, 2002 3:48 AM
> Subject: Untapered Soundboard Ribs
>=20
>=20
> > The Mehlin grand I worked on the other day had untapered ribs on its
> soundboard. Ribs on other pianos are somewhat abruptly tapered near =
the
> ends. Is that so the panel will tend to move as one unit and flex =
around the
> perimeter - somewhat like a speaker cone might move with its firm cone =
and
> soft surround material that connects the cone to the basket (I kinda =
don't
> think this is really a good analogy). It would seem to me that =
untapered
> ribs are quite a departure from "the proper way to build a =
soundboard".
>=20
> You do raise some interesting questions. It is my belief that ribs in =
the
> 'modern' piano are end-tapered the way they are to accommodate the =
practice
> of compression-crowning. In this process the rib actually resists the
> formation of crown--i.e., the rib wants to remain straight but is =
forced
> into a curve by the stress interface created by the expanding =
soundboard
> panel. The rib must be kept to a reasonably consistent height and =
thickness
> if the crown radius is going to be anywhere close to uniform.

Interesting. That sure does make a lot of sense. Should work also.

> Even as most manufacturers began converting from compression-crowning =
to
> rib-crowning techniques (or some combination of the two) the =
traditions of
> rib sizing and feathering carried over.

Hey man, we gotta do it like the masters!

> The problem, of course, comes at the parameter where the tall ribs =
will
> restrict the motion of the vibrating panel. More or less--considering =
the
> range of motion of the typical soundboard, however, there really isn't =
a lot
> of bending going on around the parameter of the soundboard. So, in =
real
> life, that untapered (un-feathered) rib may not matter all that much.
> Indeed, it may well help through the killer octave region.
> >
> > If soundboards vibrate their various frequencies in small random
> (seemingly) areas of the board...
>=20
> Don't confuse reality with desirability. Just because the typical =
soundboard
> does break up into a myriad of miscellaneous resonances doesn't me =
this is
> the ideal. Or that this is desirable.
>=20
> > ...why do we taper ribs like we do (the abrupt taper near the end). =
Why
> not an even taper along the entire rib? Or no taper?
>=20
> Why not indeed. Have you ever seen the ribs on one of our soundboards? =
It's
> been some years since we've feathered anything in the conventional =
manner.

No I have not. I have seen the Walter grand - but I don't remember the =
rib tapering. I'll just have to see your stuff sometime! Thank you for =
your thoughts.

> Del
>=20

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