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 >
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