Killer Octave

[Ron Overs]

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.

>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.

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').

>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.

>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.

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.

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.

Ron O
-- 
Overs Pianos
Sydney Australia
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Web site: http://www.overspianos.com.au
Email:     mailto:ron@overspianos.com.au
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