bridge physics

[Ron Nossaman]

Hi gang,

first, a reply


At 11:43 AM 4/17/97 -0600, you wrote:
>I'm not so sure that just because static friction is broken by rendering in the horizontal plane, that it would be broken in the vertical plane at the same time.  Hmmm... guess its time for me to check with my local physicist again.
>
>In addition, I think it should be pointed out in this discussion that the downbearing of an individual string is fairly small - on the order of a couple of pounds. So the friction required to keep the string slightly off of the bridge isn't that great
>


I suppose this one could be a function of how beat up the pin is as well as the downbearing pressure. Horace mentioned the condition of the strings too. Too many variables. Bad question, disregard.



>As to the ability of the hammer to lift the string off of the bridge.  I'm not as sure of that as I was a couple of weeks ago (this list will do that to you) I think, as Ron Says, that humidity shifts have a lot more to do with it in normal circumstances
..  I do maintain, however, that a hard blow, especially in the upper treble where the hammer is a lot closer to the bridge, can create some movement.
>
>John McKone, RPT
>St. Louis Park, Minnesota
>(612) 280-8375
>"Sleepless in Minnesota"


This is the one I wanted. In the upper treble, the strike point is closer to the bridge, but also closer to the capo. The strike point expressed as percentage of speaking length from capo in the high treble isn't that much different from the lower tenor w
here the problem doesn't occur (degree, degree, no split hairs). The string excursion isn't nearly as wide, with a string of considerably less total mass in the upper treble as well. Why won't swinging a heavy string through a wide path put a string up a
bridge pin as readily as swinging a lighter string through a narrow one will? Doesn't compute, there's data missing here.

Also, I brought you all another log for the fire. Consider this.

The bridge pins are angled. The narrowest stagger is at the bridge surface. See it coming? If a string were knocked from the bridge surface to any point above that, it would hang at a point where the string section between the bridge pin contact points wa
s WIDER than that at the bridge surface. The stagger gets wider as you go up the bridge pins. With the overall string length from hitch pin to tuning pin remaining constant, the string must take a longer path to get through the bridge. The vertical deviat
ion would also be minutely greater. The string can't get slack anywhere to go this extra distance, so it has to stretch. If this is a real thing, it HAS to go SHARP! Have you ever personally experienced a well tuned piano (one you did yourself, so the qua
lity of tuning isn't in doubt <G>) being beat SHARP?

With the string tension increasing as it's pushed up the pins, it would take proportionately more force to drive a string up a pin, the higher it gets. Eventually, it would get as high as it could go with the force available to raise it. Why, in all the p
ianos we see, with all the tension and bearing ranges available, don't we see a string that reached this logical equalibrium with the string 1/16" above the bridge? It's never more than a couple of thousanths. Not enough to see. Why? If it's possible to k
nock a string up a bridge pin, why don't we see ANY of what I have just described?


Please note, I changed the subject to "bridge physics". The "bridges/seating" thread is beginning to fragment and wander into the weeds. I'd like this to stay as tightly focused as possible, PLEASE, until a few more points are either ironed out, or abando
ned for lack of further ideas. I feel that some remarkable progress is being made here and I'd like it not to degenerate into stories, low-incidence exceptions, and peripheral errata just yet. I think there is still something valuable here and I want it.
I don't care that it has already blown some of my long-cherished ideas to flitters, I want it. There are better truths to be had. If we can just hack through enough of our own preconceptions and look at this the right way, maybe we can finally see it look
ing back at us and identify it. Then we'll send out for beer and swap lies. Thanks.


Regards,
 Ron Nossaman