Killer Octave Question

[Delwin D. Fandrich]

----- Original Message -----
From: <A440A@aol.com>
To: <pianotech@ptg.org>
Sent: Thursday, April 10, 2003 7:06 PM
Subject: Re: Killer Octave Question


>    There is evidence for debate on the arch theory. The observed change in
> the Mason & Hamilin centripedal resonator when the strings are removed.
In
> every case I have seen, (more than several), destringing a Mason changes
the
> tension on the bars, ( judged by rattles that appear when destrung).
>    Perhaps the strongest indication I know of that the arched board
attempts
> to spread the case is the Chickering grands with the inner rim.  All of
these
> pianos,(I have had 4 of them), when destrung, show the inner rim to come
> inwards.  A wedge that is very lightly placed between the inner and outer
rim
> before stringing will be extremely tight when the strings are pulled up to
> pitch and the screws that pass from inner to outer around the perimeter
will
> also be looser.  There is definitely outward movement of the relatively
> flexible inner rim under downbearing pressure.  If the board simply
presses
> downward on the shelf, this particular construction, with its cantilevered
> support, would bend inwards, no?

Well, there is movement. Though none of this supports the arch theory. The
numbers just don't add up.

When tension is applied to a set of piano strings a whole lot of things
move. Contrary to popular myth piano plates are not completely rigid
structures. Neither are piano rims. Both move and twist as something like
35,000 to 40,000 lbs of force are applied to them. Sometimes by quite a lot.

Del




> These Chickerings also have really nice
> sound with virtually no bearing, even though without any strings on them,
> there is a boatload of bearing  They simply flatten out and I have, in the
> past, attempted to add bearing by lowering nosebolts,but the board just
keeps
> on flattening out as I do.
>     The unsupported span of the belly rail on grands often has a slight
curve
> outwards between the horn and their attachment to the treble case side.  I
> don't think this was built into the pianos originally, so  what other
force
> but soundboard spread would do this?

It's hard to say where this comes from--I would guess from natural wood
movement over the years. I doubt you're going to be able to see the 0.001"
or so of distortion that might possibly be contributed by the rib flattening
out. Assuming, of course, that the both rim assembly and the rib itself are
made of a material that is perfectly non-compressible materials.

Del