Killer Octave

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Overs" <sec@overspianos.com.au>
To: <pianotech@ptg.org>
Sent: September 09, 2001 6:12 AM
Subject: Re: Killer Octave


> Del etc.
>
> Del wrote;
>
> >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.
>
> But it is vibrating excessively because the hitch plate is light and
> the added coupling of the bell is inadequate. Fixing a nut to the
> under side of the bolt head or on either side of the bell attachment
> hole will do little to prevent the vibration. It is a systemic lack
> of rigidity which is allowing the vibration to assume the magnitude
> it does.

My point being that if the bell and the coupling bolt are doing their job
there won't be a lot of vibration either in the bell, the bolt or in the
plate panel.

I guess I still don't understand why you are finding a problem with this
device. It's really rather effective at doing its job.



> Yes I agree, but my point is that it's not rigidly coupled enough and
> the plate's too light. Interestingly, the latest Hamburg S&S plates
> are a little heavier in section thickness (these are only ones we see
> in Aus').

Even more interesting since I've been led to believe that the plates used in
the Hamburg pianos are now coming from the same foundry making the NY
plates. OS Kelly being now owned by S&S.



> >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.
>
> Indeed it will, but a belly brace and set bolt would increase the
> sustain time further than that which is achieved by the bell, since
> it would hold the hitch plate more securely to prevent it waving
> about like a flag in a breeze.

Well, I'll be interested in your actual results once you've done this.



> Agreed, but systemic damping is what we are trying to avoid if we are
> looking for sustain. Holding a light plate with a coupling such as
> the bell with its poor mechanical advantage is hardly an effective
> way to build sustain into an instrument. Your mention of the casting
> freeze rate may also be of significance, since modern castings tend
> to have longer freeze times. This results in softer castings with
> higher hysteresis loss potential. We might therefore consider the
> possibility that plate vibration in more recently poured plates might
> result in higher energy losses.

Perhaps damping was a poor choice of terms. Damping is what you get with a
nosebolt going into wood, wood being a much more effective damper than iron.
The bell/bolt arrangement actually adds some stiffness to the system. By
actual measurement I do know that it reduces the amplitude of vibrations in
the plate panel. It also raises the frequency of what resonances remain.



> This is the very thing which got me into winging about the bell in
> relation to the killer zone, as a possible contributing factor to
> short tone. Everybody's talking about the short sustain in the killer
> zone. Energy losses will occur in any mechanical system where there
> is energy transmission with any degree of hysteresis loss. If the
> plate vibrates it will lose string energy. The greater the amplitude
> of plate vibration the greater the loss. If the sound board flops and
> flexes all over the place as it vibrates (as a consequence of low rib
> and/or bridge heights), instead of moving more or less uniformly, it
> will lose relatively more energy in the form of heat also. The string
> won't care what causes the energy losses, it will still cause the
> sustain to be shorter.

Exactly my point. The bell/bolt arrangement does reduce energy losses due to
plate vibrations. Running a nosebolt into a wood beam may reduce them as
well, but probably not as much due to the higher damping qualities of wood.

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