"Oval or Round Shanks" or to bend or not to bend

[Richard Moody]

Marcel wrote...
	"I think that you forget to take into consideration the
deceleration of the
 hammer when it hits the string"

The last sentence of my post alluded to this. "...consider  the
most important phenomena, what happens to the string during and after
hammer contact?"
	So on to this crucial part of the hammer's travels.  After letoff,
there is an instant of time, and a bit of space the hammer travels
free from the action save the center pin and its bushings. The hammer
strikes the string, then bounces off, and is caught by the back
check. What happens during this tiny moment of contact with the
string has undergone extensive analysis.  Starting with how you name
it, and Marcel's term "power to tone ratio" sounds good.  
	Before time lapse photography, only educated proposals could be
made. It was suggested that the optimum blow to the string would
occur if the  hammer rebounded at the moment the string was at the 
heighth of its vibration peroid.  The force of the hammer pushes the
string up.  At some point the hammer leaves the string, in what is
called rebound.  Several factors are supposed to affect this rebound.
 But the imaginary perfect rebound should be at apex of the string's
vibration plane.  It has been suggested that the hammer can leave the
string before this happens and after this happens.  If the hammer
rebounds before max heighth, higher partials are excited more than
the lower ones, and thus the bright, brassy, shrill tone.  If the
hammer leaves the string after max height, energy is robbed from the
vibration, ie, instead of the hammer rebounding, the downward cycle
of the string is pushing the hammer off, and thus a muffled tone. It
was also suggested, and all of this is by Helmholtz I believe, that
the ideal tone should consist of 50% of the fundamental, and 50% of
the rest of the partials. And this would occur...??...??... if the
hammer left the string just at max height of vibration.  In this
scenerero the string really doesn't care what the hammer does before
it hits it, only how far it gets  pushed. If the hammer stays on the
string after this, that is a problem. 
	So as Marcel suggests hammer contact time with the string is a
matter of voicing, at least as far as technicians in the field are
concerned.  However we can't determine if the hammer is acting
according to ideal paradigms execpt through what we hear. The only
variable we can control is the density of the felt through voicing.
And even then, I think all we are really doing is removing the
hardness in the grooves. All other needling away from this area is
superflous for the most part, but that is my humble opionon only or
in the internet vernacular, IMHO. If hammer shank flex due to contact
with the string is occuring, that is beyond our means at the present
to adjust. 
 However once the piano is in the shop being outfitted with new
hammers and shanks a few more factors can be considered. 

Richard Moody 
	


----------
> From: Marcel Carey <mcpiano@multi-medias.ca>
> To: pianotech@ptg.org
> Subject: Re: "Oval or Round Shanks" or to bend or not to bend
> Date: Thursday, September 04, 1997 5:37 AM
> 
> Richard & List,
> 
> I think that you forget to take into consideration the
decceleration of the
> hammer when it hits the string. The decceleration is much much more
than the
> acceleration. The hammer stops right there and then the shank will
have to
> flex to absorb that decceleration. The hammer has about 1-7/8" to
accelerate
> as it stops almost on the string (mind you, I know the string will
move
> around a bit). I think this is where the shanks flexibility will
affect the
> string contact time. And we all know that string contact time
equals
> voicing. So there must be an ideal compromise to be made depending
on pianos
> in order to get the "ideal" power to tone ratio.
> 
> Who knows, even I could be right.
> 
> Marcel Carey, RPT
>