Springiness of Parts Was Re: Key Leads and Inertia

[Bill Ballard]

At 10:12 AM -0700 4/29/03, Delwin D. Fandrich wrote:
>  >From: "Classic Touch Ent" <classictouchent@comcast.net>
>  >Greetings Del,
>  >        Thanks for resurrecting key bend energy loss as an issue. Is it
>>  primarily energy lost or does it amount to energy delayed? Both? Is the
>>  'delay' sufficient to amount to 'loss"? How quickly does the key
>>  'remember' it s original shape?
>
>It is mostly delayed. But, if it is delayed until after the hammer has
>struck the strings it's a moot point.

"If it's delayed...." That's worth some thought.

Keys and shanks bend like springs, ie. when a deforming force is 
applied. When the bending force is removed, they restore themselves. 
The bending force in the action's case is the pianist's stroke/blow. 
A staccato blow can be hard or soft, but usually it doesn't drive all 
the way down to the bottom of dip. At the point where it stops short 
(25%, 45%, 70% of the way to let-off) the key and shank can start to 
restore themselves. Of course at this point, the action parts have 
only their momentum to protect them from the decelerating effects of 
friction and gravity.

A rapid trill could be viewed as a staccato passage, two notes 
alternating. This would be an excellent example of action play where 
the driving force on the key stopped well short of dip, allowing the 
key and the shank time to straighten themselves out.

Here again, the spring-like behavior of the action is directly 
proportional to two things, the driving force and the inertia of that 
action. In fact the extent to which inertia *can* resist acceleration 
(and that is for a very brief instant at the outset), inertia 
provides a "mounting block" for the springiness of the parts.

Speaking of springy action parts, I'd imagine the knuckle and rep 
cushion, although squashable, have nowhere near the springiness of 
hammer crown felt. The rep with its short stocky body, supporting the 
knuckle's load with the long end grain of the jack, probably wouldn't 
bend much.

Bill Ballard RPT
NH Chapter, P.T.G.

"When writing a mental note, first procure a mental piece of paper"
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