Killer Octave

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Overs" <sec@overspianos.com.au>
To: <pianotech@ptg.org>
Sent: September 08, 2001 7:00 PM
Subject: Re: Killer Octave


> Sorry about the poor nomenclature of the previous post, it should have
read;
>
> . . . . . While on the topic of the killer zone, I suspect that the
> 'tone bell' of Steinway pianos might indeed be a 'tone dissipator'.
> If you check the location of the connection bolt from 'bell' to
> plate, you will notice that it connects adjacent to the so called
> 'killer' zone, or should we say 'killed' zone. Just last week I
> crawled under a D to feel the movement at the bell connection bolt
> under heavy playing (try it - you'll be amazed). The next D I rebuild
> (if it ever happens again) will likely get another beam and set bolt
> in place of that suspect device. I'm not suggesting that the problem
> is the 'bell' alone, but I suspect it is contributing. It would be
> interesting to compare the Yamaha CFs with and without the tone bell.
> Gosh its good to see marketing dictating design as usual isn't it?
------------------------------------------------------

Instead of removing the bell you might try leaving it in place and adding a
wood brace--i.e., another belly-brace--between the inside treble curve and
the bellyrail. If you don't like how much the bolt vibrates you might try
threading the hole in the plate and installing a larger (fully-threaded--in
fact, you may have to thread the bolt yourself) bolt in place of the
original. Then you can also put a nut on top of the bell and another on the
bottom making the connection somewhat more solid.

The bell does really serve a somewhat useful function, though it's not the
one S&S has been telling us about. And, no. It has nothing to do with the
Magic Circle of Sound. The bell, along with the coupling bolt, mass-couples
the plate to the inner rim. Taking the bolt out--you can do this even with
the piano tuned to pitch, it's not structural--allows the plate to move in
response to the energy in the string backscale and in most pianos will
result in a reduction in sustain time. How much energy loss--hence, how much
of a loss of sustain time--there is in the plate at this point depends
apparently on the precise characteristics of the individual plate--it's
thickness, and certain mechanical characteristics dependent on the pouring
and cooling rate of the casting, etc.--but there is a measurable amount of
vibration in that area that is damped by the bell and coupling bolt.

Del
Delwin D Fandrich
Piano Designer & Builder
Hoquiam, Washington  USA
E.mail:  pianobuilders@olynet.com
Web Site:  www.pianobuilders.com