>I understand Ron to be saying that it is not necessary for the string to >terminate simultaneously at both the pin and the bridge edge. If that >understanding is accurate, I wonder if that opinion is generally shared. The notch edge in front of the bisection of the pin (into the speaking length) can cause tonal clarity problems. A notch edge behind the pin bisection (into the bridge) won't unless the pin is loose in the cap. Look at bridge notching in the pianos in the exhibition hall in Nashville this summer and see (and listen) for yourself. >>>>At the same time, compression on the bridge top (exacerbated by tapping >>>>down on the strings) lowers the contact point on the bridge. >>> DS >>>Assuming enough downbearing ( at some point in time) to compress the >>>wood fibers, I would place more responsibility on the seasonally induced >>>increase in downbearing more than the unsubstantiated certainty of >>>aggressive tapping. And, of course, there is the speculation that the >>>bridge surface itself rides up the pin in humid conditions, in turn, >>>pushing the string further up the pin. >> RN >>This isn't speculation. It can be easily enough measured by anyone >>willing to take the time and trouble to do so. > >Am I being irresponsible if I believe you on this without testing it >myself? "Speculation" was a poor choice of words. I just wasn't sure that >any definitive study of this phenomena had been conducted, and was thus >reluctant to make an unsupported assertion. I'd love to know if such >documented data exists. As far as I know, only the data I am accumulating myself. I have no doubt that someone at some time has been aware of this stuff, but I know of no "definitive" study. > Should I assume that the remainder of my statement concurred with your > views? No. It isn't primarily downbearing that is crushing bridge notch edges. It's more cyclic seasonal dimension changes of the bridge cap pushing the string up the pin against the friction of the string against the pin, and pin angle. > DS >>>The question there would be whether the string then follows the board >>>back down in the dry season. >> RN >>This can also be measured. > >Is this conceptual model commonly shared by other readers? What, the concept of measuring rather than taking a consensus? >>No pin will remain bottomed in the hole with the bridge changing overall >>height with humidity swings. The point of zero relative movement between >>the bridge and the pin is typically somewhere near the bottom of the cap >>- depending on the type of capping material used. That means that as the >>bridge top is going up the pin, the bottom of the hole is getting deeper, >>and moving away from the base of the pin. > >Ron, I can picture what you're describing but I can't grasp the >methodology by which you determined it. Can you explain it? A model bridge section, with vertically laminated root and solid quarter cut cap, taken from about 4%MC to about 12%MC - Root height went from 0.842" to 0.868", or +0.26" height change. Cap height went from 0.253" to 0.119", or +0.004" height change. Pin height above the cap went from 0.026" to 0.119", or -0.008 height change. If the pin height lessened by 0.008" as the cap height increased by 0.004", the point of zero relative movement between the bridge and the pin is somewhere a couple of thousandths into the bridge root below the cap. As the root height increases, the hole the pin was installed in increases in depth, to the same percentage of overall height change the root experienced. Since the pin doesn't change dimension with humidity changes, the bottom of the hole it's in has to recede from the bottom of the pin. >Do you assume that the pin, once so displaced, would return to its >bottomed position in the following dry season, or rather that it remains >elevated? The point of zero relative movement between pin and bridge should remain in about the same spot through repeated cycles. If, one extra severe winter, the root gets drier than it's ever been before, the pin will be pushed up a bit, where it will stay. >If so, wouldn't the pin eventually work its way out of the bridge? No. Have you had problems with pins working their way out of the bridges in all the pianos you've ever seen that experience seasonal humidity fluctuations? >Assuming you cared about having the string contact the front of the >bridge, do you agree that tapping the bridge pin rather than the string >would achieve that end? I do care about the string contact with the front of the bridge, but I do not agree that tapping the pin will achieve that end. That's the whole point of all this. If the string isn't contacting the notch edge, it's for a reason that tapping neither string, nor pin will cure. >I think we may agree, but I'm not sure. If you conceive of Front Bearing >as that part of the total downbearing which pulls the bridge mass forward, >then I can understand the configuration you describe above. Front bearing is the angle between the string segment on the bridge top and the speaking length segment. >As it relates to termination however, Front Bearing, as I understand it, >is precisely about the relationship of the vibrating string segment to the >front edge of the bridge and those few millimeters behind the edge. If >that edge is below the line formed by the apex of the bridge and the front >string terminus, then a seated string will describe a negative front >bearing angle. Any noise elimination achieved by such seating will be >temporary, as you point out. As I point out. I've also pointed out that this local negative front bearing from tapping a string down isn't to be considered to be overall front bearing. It results from doing something that isn't indicated from the cause of the symptoms - seating strings. >I'll admit however, I'm confused. You say the string does NOT climb the >pin, yet, in the above example you point out that the tapped string will, >in fact "straighten back out". Wouldn't this qualify as climbing the pin, >since I don't believe you are saying that either the bridge surface or the >pin is responsible for the string's re-elevation. No, that doesn't qualify as climbing the pin. The string segment, courtesy of the tension it's under, merely returns to as straight a line between it's end supports (in all planes) as it can. If the notch edge just happens to be below that horizontal plane, the string won't be contacting it. Of course the bridge surface is responsible for this. It's one of the horizontal support points for the string. It's just that this support point doesn't necessarily correspond with the notch edge. >If you are not concerned about the pin and notch terminating the string >simultaneously, as you seemed to indicate at the beginning, then it would >seem that negative front bearing is not a problem for you. Of course it's a problem for me. I think I've indicated to you a half dozen times or so that I don't consider negative front bearing to be acceptable in a typical piano. If I haven't up to now, I just did. I don't expect that opinion to change, but I'll notify you if it does. >The question remains for me, whether there is any audible or measurable >difference between the vibrational pattern of a string which terminates >simultaneously at pin and notch, and one which lacks a defined, horizontal >edge. Depends on where the termination is in relation to the pin, as described above, and whether or not the pin is tight in the bridge. Ron N
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