On Wed, Jan 6, 2010 at 11:10 AM, Ron Nossaman <rnossaman at cox.net> wrote: > William Monroe wrote: > >> George, >> >> Let me first say how much appreciation I have for your contributions to >> this list. Invaluable. And certainly your experience is far greater than >> mine. However, I would disagree with your assessment. >> >> Of course I understand that removing leads adds downweight. I addressed >> that. I would disagree however, with the assessment that inertia only comes >> into play until.......[acceleration of gravity]. An object at rest tends to >> remain at rest. The heavier the key, regardless of DW/UW the more effort >> required to start the key moving. Make a key entirely out of lead and >> balance it out at 50g DW. Take a standard key and balance at 55g DW. It is >> very clear that the inertia of the lead key will make the instrument >> unplayable. Inertia comes into play immediately, and a high inertia key >> will be less responsive and more difficult to play, even with a lower DW. >> Yes? Or am I missing a few cells.......... >> > > Hi Bill, > What's the formula for force? It's mass*acceleration, right? The only > reason there is lead in the key in the first place is to (almost, less DW) > counterbalance the (mostly) hammer mass out there on an *5+ lever. But > that's just static balance. What happens dynamically? While the higher mass > of the key is being accelerated downward, the lesser mass of the hammer is > being accelerated upward at (less action compliance) roughly five times the > acceleration rate. As the force and therefore the acceleration rate of the > key stroke increases, which side of the system has the biggest inertia > problem? It's not the key leads, it's the hammer weight. I've heard the > story about key leads exceeding free fall speed during play and I think it's > another of those "intuitive" things that just ain't so in the real world. > Key leads aren't all alone out there falling in space. They're on one side > of a lever, with more effective weight (less mass on a longer moment arm) on > the other. The inertia should work similarly in the absence of gravity > during the power stroke. Get the action ratio and hammer weight under > control and there won't be inertia problems from the action. Key leads are > just an indication of how the rest of the action is set up - a result, not a > cause. > > Same thing from another angle. Del has reported on list that he's measured > the timing and movement of action parts in use. It's quite possible in a > large piano with long keys, for the key to bottom out on the front punching > with a hard blow, before the hammer moves. Where's the inertia effect here? > The key flexed enough to allow the front to bottom out on the front > punching, moving key leads with it, before the hammer even moved! Imagine > that the key was infinitely stiff, and had the same overall weight and mass > distribution. Hit it just as hard as in the previous instance, and the > resistance would be considerably higher, because the hammer would be forced > to move sooner and accelerate faster. Not because of the key leads. Or > something would break - something on the side of the lever away from the key > leads. > > My take. > Ron N > OK, Frank, Ron, It appears I may be missing a few cells. Thanks for the further explanation. You were both rather kind. Of a couple things I am guilty: Thinking in terms of linear motion. Guilty. I've done that before, on this forum no less. Some of us never learn. Not paying attention enough in HS Physics. Guilty. I think I'm a classic case of knowing enough to be dangerous. The explanations you (collectively) give make sense and I can't argue against them. I guess I'm hung up on intuition. Yes, I know, bad habit. I cling to intuition even as I realize that physics still does apply in my world. So in the end, I'm not entirely wrong, yes? At *f* or *ff* blows, a heavier key stick would "resist" that initial change of direction that starts the key moving (and all subsequent changes in direction) more than a lighter key stick, right? If I get your meaning, it is more a question of usefulness, in that unless someone is playing rather heavy handedly (which an arthritic is not likely to be) the small changes of inertia we can affect would be inconsequential, and in fact be outweighed most of the time by the added DW, right? Going back to the books now. I promise to do my homework for tomorrow.......... William R. Monroe -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100106/b6d6b538/attachment.htm>
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