<html> <body> The last time I attempted to discuss this subject with Ron, my apparent inability to express my thoughts precisely enough threatened to undermine the normal civility with which these exchanges usually take place.  I am not trying to be purposely argumentative in the questions I raise, nor disrespectful.  I apologize for the length and for any continued fuzzy thinking. Even though I direct most of my comments back to Ron, I am interested to know what others think, as well. At 03:48 PM 4/1/2004 -0600, Ron wrote: <blockquote type=cite class=cite cite>DSkolnik: <blockquote type=cite class=cite cite> I'm asking "why does th= e string need to  contact  the front edge of the bridge?"</blockquote>RNossman: It doesn't. I suspect you have tuned pianos in which this was the case. I know I have. As long as the bridge pin is solid in the top of the cap, there won't be a false beat to lead someone to tap the string - or pin.</blockquote> 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.  <x-tab>       </x-tab>DLove<= br> <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite><blockquote type=cite class=cite cite> The assumption is that the strings ride up on the bridge pins.  Assuming positive bearing and proper bridge pin angles with a bridge and pins in pristine condition that is not likely.</blockquote><x-tab>        <= /x-tab>DSkolnik Most of these discussions make these assumptions, or that any evident negative front bearing is due to overly aggressive tapping.  In my experience, these are not self evident. Negative front bearing can exist (with positive net) from relatively early in the life of a piano, due to errors in manufacture, bridge roll, or other conditions inducing severe compression.</blockquote><x-tab>       &n= bsp;</x-tab>RNossman Then you apparently misunderstood what I was trying to explain to you, or I didn't explain it clearly.</blockquote> I am not sure what I misunderstood, however, I may have been unclear.  I felt that these assumptions seemed to be prevalent in the current discussions on CAUT, starting with Tuning Stability from Jeff Stickney, <x-tab>        </x-tab>DL <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite><blockquote type=cite class=cite cite>At the same time, compression on the bridge top (exacerbated by tapping down on the strings) lowers the contact point on the bridge.</blockquote><x-tab>        <= /x-tab>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.</blockquote><x-tab>        </x-= tab>RN This isn't speculation. It can be easily enough measured by anyone willing to take the time and trouble to do so.</blockquote> 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.  Should I assume that the remainder of my statement concurred with your views? <x-tab>        </x-tab>DS <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite>The question there would be whether the string then follows the board back down in the dry season.</blockquote><x-tab>        <= /x-tab>RN This can also be measured.</blockquote> Is this conceptual model commonly shared by other readers? <x-tab>        </x-tab>DL <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite><blockquote type=cite class=cite cite>Unseating on the bridge top tends to occur when the contact point on the bridge top is lower than the indentation in the side of the pin.  Therefore, you are much better off tapping down the bridge pin than the string.</blockquote><x-tab>        <= /x-tab>DS But this assumes either that the pin is not already bottomed in the hole or that you can safely drive the pin into the bridge body, like a nail.</blockquote><x-tab>        </x= -tab>RN 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.</blockquote> Ron, I can picture what you're describing but I can't grasp the methodology by which you determined it.  Can you explain it?  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?  If so, wouldn't the pin eventually work its way out of the bridge?  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? <x-tab>        </x-tab>DL <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite><blockquote type=cite class=cite cite> At worst, it can create a further disconnect as the contact point on the bridge top is lowered due to further compression of the bridge top.</blockquote><x-tab>        </x-= tab>DS Here it is again.  What do you imagine (I don't know the answer) the differential between the force needed to seat the string and that required to further indent an already compressed piece of rock maple?  I find the Compression by Tapping argument suspect.</blockquote><x-tab>        = </x-tab>RN Look up the side grain compression limit of rock maple (1470psi). Then figure the footprint in square inches of the area under a string being tapped. Make it effectively about 0.25"long and 0.010"wide. That's 0.0025 sq"*1470, or somewhat under four pounds that can be applied to the string before the crush limit of the maple is exceeded. Long term deformation will happen at a lower figure. The friction level between a new, undamaged bridge pin and a string at a 10° side bearing angle and 160 lbs of tension is over 14.5 lbs, or roughly 3.5 times the force needed to crush the bridge top under the string. An old grooved pin will have a wider string contact area and an angled depression for the string to have to be forced up as the pin is driven, so you can expect a considerably higher friction figure. By then, the string depression in the cap will be wider too, and the psi load will hopefully not be much higher than with a new pin. This is from the presumably gentler than tapping strings process of driving the pins. What do you suppose the impact psi levels are with someone tapping strings with a brass drift and a hammer? Maybe a hammer shank, since if the shank isn't damaged, the bridge won't be either. The compression limit for the end grain of that shank is listed at 17,830 psi, or over five times the side grain limit of the cap.</blockquote> Stop here for a moment. I appreciate the data and have no reason to question these figures, unless you believe that they prove that an elevated string cannot be rendered to the bridge without further compressing the surface.  <x-tab>        </x-tab>RN <blockquote type=cite class=cite cite>The point is that the edge of the bridge cap has already been crushed by the expanding bridge before anyone feels compelled to tap either strings or pins. This means that the edge of the bridge (under the string) is rounded down to lower than the center, lower than a point even a few millimeters back from the edge, and lower than a line between that point and the capo. A bridge with little (but still) positive front string bearing will have strings terminating on the bridge pin, and a spot some small distance back from the notch edge, but passing slightly above the notch edge in a straight line to the capo. This string has NOT climbed the pin, and tapping either it or the pin down will NOT make it stay down. It will straighten back out and again, not touch the notch edge, and if the pin is loose, will produce a false beat.</blockquote> 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.  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. 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. 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. 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. <x-tab>        </x-tab>RN <blockquote type=cite class=cite cite><blockquote type=cite class=ci= te cite><blockquote type=cite class=cite cite> Furthermore, false beats are usually a product of loose bridge pins and a flagpolling of the pin which creates an oscillation.</blockquote> The false beats created by loose bridge pins is different from the distortion caused by faulty termination.</blockquote> Yes they are, and these discussions need to start, and stay, with one or the other until some of the questions are answered.</blockquote> Again, Ron,  I'm confused.  In the opening comment of your reply (top) you said: <blockquote type=cite class=cite cite>As long as the bridge pin i= s solid in the top of the cap, there won't be a false beat to lead someone to tap the string - or pin.</blockquote> Yet, at the end, you seem to acknowledge that there is can be some distortion related to what I called faulty termination, by which I was referring to "unseated" string.  What I can tell you is that before it gets too humid, I'm going to try tapping some bridge pins, just to see.  I'm open. David Skolnik </body> </html>