---------------------- multipart/alternative attachment The last time I attempted to discuss this subject with Ron, my apparent=20 inability to express my thoughts precisely enough threatened to undermine=20 the normal civility with which these exchanges usually take place. I am=20 not trying to be purposely argumentative in the questions I raise, nor=20 disrespectful. I apologize for the length and for any continued fuzzy=20 thinking. Even though I direct most of my comments back to Ron, I am=20 interested to know what others think, as well. At 03:48 PM 4/1/2004 -0600, Ron wrote: >DSkolnik: >> I'm asking "why does the string need to contact the front edge of the= =20 >> bridge?" >RNossman: >It doesn't. I suspect you have tuned pianos in which this was the case. I= =20 >know I have. As long as the bridge pin is solid in the top of the cap,=20 >there won't be a false beat to lead someone to tap the string - or pin. I understand Ron to be saying that it is not necessary for the string to=20 terminate simultaneously at both the pin and the bridge edge. If that=20 understanding is accurate, I wonder if that opinion is generally shared. DLove >>> The assumption is that the strings ride up on the bridge=20 >>> pins. Assuming positive bearing and proper bridge pin angles with a=20 >>> bridge and pins in pristine condition that is not likely. >> DSkolnik >>Most of these discussions make these assumptions, or that any evident=20 >>negative front bearing is due to overly aggressive tapping. In my=20 >>experience, these are not self evident. Negative front bearing can exist= =20 >>(with positive net) from relatively early in the life of a piano, due to= =20 >>errors in manufacture, bridge roll, or other conditions inducing severe=20 >>compression. > RNossman >Then you apparently misunderstood what I was trying to explain to you, or= =20 >I didn't explain it clearly. I am not sure what I misunderstood, however, I may have been unclear. I=20 felt that these assumptions seemed to be prevalent in the current=20 discussions on CAUT, starting with Tuning Stability from Jeff Stickney, DL >>>At the same time, compression on the bridge top (exacerbated by tapping= =20 >>>down on the strings) lowers the contact point on the bridge. >> DS >>Assuming enough downbearing ( at some point in time) to compress the wood= =20 >>fibers, I would place more responsibility on the seasonally induced=20 >>increase in downbearing more than the unsubstantiated certainty of=20 >>aggressive tapping. And, of course, there is the speculation that the=20 >>bridge surface itself rides up the pin in humid conditions, in turn,=20 >>pushing the string further up the pin. > RN >This isn't speculation. It can be easily enough measured by anyone willing= =20 >to take the time and trouble to do so. Am I being irresponsible if I believe you on this without testing it=20 myself? "Speculation" was a poor choice of words. I just wasn't sure that= =20 any definitive study of this phenomena had been conducted, and was thus=20 reluctant to make an unsupported assertion. I'd love to know if such=20 documented data exists. Should I assume that the remainder of my statement= =20 concurred with your views? DS >>The question there would be whether the string then follows the board=20 >>back down in the dry season. > RN >This can also be measured. Is this conceptual model commonly shared by other readers? DL >>>Unseating on the bridge top tends to occur when the contact point on the= =20 >>>bridge top is lower than the indentation in the side of the=20 >>>pin. Therefore, you are much better off tapping down the bridge pin=20 >>>than the string. >> DS >>But this assumes either that the pin is not already bottomed in the hole= =20 >>or that you can safely drive the pin into the bridge body, like a nail. > RN >No pin will remain bottomed in the hole with the bridge changing overall=20 >height with humidity swings. The point of zero relative movement between=20 >the bridge and the pin is typically somewhere near the bottom of the cap -= =20 >depending on the type of capping material used. That means that as the=20 >bridge top is going up the pin, the bottom of the hole is getting deeper,= =20 >and moving away from the base of the pin. Ron, I can picture what you're describing but I can't grasp the methodology= =20 by which you determined it. Can you explain it? Do you assume that the=20 pin, once so displaced, would return to its bottomed position in the=20 following dry season, or rather that it remains elevated? If so, wouldn't= =20 the pin eventually work its way out of the bridge? Assuming you cared=20 about having the string contact the front of the bridge, do you agree that= =20 tapping the bridge pin rather than the string would achieve that end? DL >>> At worst, it can create a further disconnect as the contact point on=20 >>> the bridge top is lowered due to further compression of the bridge top. >> DS >>Here it is again. What do you imagine (I don't know the answer) the=20 >>differential between the force needed to seat the string and that=20 >>required to further indent an already compressed piece of rock maple? I= =20 >>find the Compression by Tapping argument suspect. > RN >Look up the side grain compression limit of rock maple (1470psi). Then=20 >figure the footprint in square inches of the area under a string being=20 >tapped. Make it effectively about 0.25"long and 0.010"wide. That's 0.0025= =20 >sq"*1470, or somewhat under four pounds that can be applied to the string= =20 >before the crush limit of the maple is exceeded. Long term deformation=20 >will happen at a lower figure. The friction level between a new, undamaged= =20 >bridge pin and a string at a 10=B0 side bearing angle and 160 lbs of= tension=20 >is over 14.5 lbs, or roughly 3.5 times the force needed to crush the=20 >bridge top under the string. An old grooved pin will have a wider string=20 >contact area and an angled depression for the string to have to be forced= =20 >up as the pin is driven, so you can expect a considerably higher friction= =20 >figure. By then, the string depression in the cap will be wider too, and=20 >the psi load will hopefully not be much higher than with a new pin. This=20 >is from the presumably gentler than tapping strings process of driving the= =20 >pins. What do you suppose the impact psi levels are with someone tapping=20 >strings with a brass drift and a hammer? Maybe a hammer shank, since if=20 >the shank isn't damaged, the bridge won't be either. The compression limit= =20 >for the end grain of that shank is listed at 17,830 psi, or over five=20 >times the side grain limit of the cap. Stop here for a moment. I appreciate the data and have no reason to=20 question these figures, unless you believe that they prove that an elevated= =20 string cannot be rendered to the bridge without further compressing the=20 surface. RN >The point is that the edge of the bridge cap has already been crushed by=20 >the expanding bridge before anyone feels compelled to tap either strings=20 >or pins. This means that the edge of the bridge (under the string) is=20 >rounded down to lower than the center, lower than a point even a few=20 >millimeters back from the edge, and lower than a line between that point=20 >and the capo. A bridge with little (but still) positive front string=20 >bearing will have strings terminating on the bridge pin, and a spot some=20 >small distance back from the notch edge, but passing slightly above the=20 >notch edge in a straight line to the capo. This string has NOT climbed the= =20 >pin, and tapping either it or the pin down will NOT make it stay down. It= =20 >will straighten back out and again, not touch the notch edge, and if the=20 >pin is loose, will produce a false beat. I think we may agree, but I'm not sure. If you conceive of Front Bearing as= =20 that part of the total downbearing which pulls the bridge mass forward,=20 then I can understand the configuration you describe above. As it relates= =20 to termination however, Front Bearing, as I understand it, is precisely=20 about the relationship of the vibrating string segment to the front edge of= =20 the bridge and those few millimeters behind the edge. If that edge is=20 below the line formed by the apex of the bridge and the front string=20 terminus, then a seated string will describe a negative front bearing=20 angle. Any noise elimination achieved by such seating will be temporary, as= =20 you point out. I'll admit however, I'm confused. You say the string does NOT climb the=20 pin, yet, in the above example you point out that the tapped string will,=20 in fact "straighten back out". Wouldn't this qualify as climbing the pin,= =20 since I don't believe you are saying that either the bridge surface or the= =20 pin is responsible for the string's re-elevation. If you are not concerned about the pin and notch terminating the string=20 simultaneously, as you seemed to indicate at the beginning, then it would=20 seem that negative front bearing is not a problem for you. The question remains for me, whether there is any audible or measurable=20 difference between the vibrational pattern of a string which terminates=20 simultaneously at pin and notch, and one which lacks a defined, horizontal= =20 edge. RN >>> Furthermore, false beats are usually a product of loose bridge pins=20 >>> and a flagpolling of the pin which creates an oscillation. >> >>The false beats created by loose bridge pins is different from the=20 >>distortion caused by faulty termination. > >Yes they are, and these discussions need to start, and stay, with one or=20 >the other until some of the questions are answered. Again, Ron, I'm confused. In the opening comment of your reply (top) you= =20 said: >As long as the bridge pin is solid in the top of the cap, there won't be a= =20 >false beat to lead someone to tap the string - or pin. Yet, at the end, you seem to acknowledge that there is can be some=20 distortion related to what I called faulty termination, by which I was=20 referring to "unseated" string. What I can tell you is that before it gets too humid, I'm going to try=20 tapping some bridge pins, just to see. I'm open. David Skolnik ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/caut.php/attachments/94/d0/7d/db/attachment.htm ---------------------- multipart/alternative attachment--
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