David and all?
A couple factors which may have affect on this issue have not been discussed.
1. A twist or fraction of a twist in a treble string could impose a force to roll the string up or down a bridge pin rather than slide. I suspect many have accidental twists or partial twists.
2. String curvature memory from having once been coiled which is visible in string removed after 30 years of being at pitch. This could have different affects depending on how this curvature is oriented.
My experience with our D was a definite perceptible improvement in sustain, power, and clarity to some notes from taping once judiciously/gently down on every bridge pin in the killer octave. On some strings, the tuning pitch dropped three or more BPS, on others it had no affect.
-Mike Jorgensen
> ----------
> From: David Skolnik
> Reply To: College and University Technicians
> Sent: Wednesday, April 7, 2004 7:15 AM
> To: College and University Technicians
> Subject: Re: Strings riding up (was Tuning stability)
>
> Ron and all ?-
> Distracted by life for a few days, the response I had begun threatens to relinquish relevance, if it had any to start. The topic has attracted some other views within the last few days, but I think there are details here that merit addressing. There are those who consider the practice of tapping strings a useful, if temporary tool at their disposal, though no significant insights into why. A combination of the video that Ed Sutton is pressing for along with a harmonic analysis seems technologically feasible ($$??).
>
> At this point, I strongly suspect that no one else is plowing through these opuses, so you (Ron) should feel no obligation to continue, unless you feel I am severely misrepresenting your views. At the end (literally) I find myself in agreement with what you would like to see.
>
> At 01:56 AM 4/4/2004 -0600, Ron Nossman wrote:
>
> DSkolnik
>
>
> I can readily see where the string would find it difficult to move upward against both the friction and the vector force, but could imagine it displacing downward, against less friction and in the direction of vector force.
>
> RNossman
> Which is why the string follows the bridge top back down the pin in dry cycles. There is, as David love said, a chance that pin damage already incurred by this wear to interfere with both the upward and downward motion of the string.
>
> DSkolnik
> With all due respect, David Love's comments represent a theoretical conjecture, just as do my comments and at least one or two of your own. On the one had, the string moves up and down the pin with the climate cycles, yet you dismiss the idea that the string could do the same, in a downward movement, in response to vibrating energy. You're stating, I think, that the friction, or mechanical capture by the pin's abraded and notched surface would prevent any significant sliding movement at the pin. On the one hand, I would say, OK, let's assume that, so we could examine the ramifications. On the other hand, it seems that at some amount of unsupported length behind the front bridge pin, the mechanical resistance to some sliding movement would be overcome. In that case, the question would then be, how much length and how much sliding.
>
> At some point too, it would make sense to discuss the more precise nature of the pin damage we speak of, what causes it, what it really looks like, and how it might affect both tone and string motion.
>
> DS
>
>
> Nevertheless, it should be possible to estimate the additional load of a pitch rise of, say 440 to 445.
>
> RN
> Yes, it is. This comes up on the list every few months. An arbitrarily chosen scaling file shows, at 435, 36168lbs total tension, and 682lbs total down bearing (calculated from bearing angles and tensions). The same piano at 440 shows 37004lbs total tension, and 697lbs total down bearing.>
>
>
> Thank you
>
> DS
>
>
> I should be able to do it, but can't, yet. It just seems that whatever rise could be attributed to board height increase would be pure load, not the pinching of the string by an expanding bridge top against angled pins.
>
> RN
> Even with negative front bearing? Have you ever measured zero or negative overall bearing in a piano that has gone sharp with a humidity increase? I have, and that doesn't fit your scenario.
>
>
> What scenario? In a piano with positive bearing, whatever increase in board height that occurs would add some additional load to the bridge (assuming pitch is not lowered immediately) without engaging the crushing dynamic of bridge surface pushing against strings locked against pins. You're right that it seems counter-intuitive to see a climate related pitch rise with negative net downbearing. Certainly it is not contradictory where you are dealing only with negative front downbearing.
>
> RN
>
>
> Besides, it's not the rise that's the issue. It's the change in bridge surface relative to the pin. Fifteen pounds of extra bearing divided up among 230 or so strings isn't going to put a heck of a lot more pressure on the bridge cap under each individual string compared to the 20+ pounds the bridge top takes at each pin pushing the string up the pin.
>
>
> As Ed Sutton suggested yesterday, referring to the string grooves in the bridge, "I believe the compressed wood is more stable than new wood." That wood doesn't keep compressing, does it? Does the At some point, it seems that some equilibrium is reached between the
> recurring crush cycle and the wood fibre damage. A while ago you supplied the information that the side grain compression limit of mock maple was 1470psi. Does this figure, in fact, change, once the surface layers are damaged?
>
> DS
>
>
> Likewise, you or someone else in possession of a brain might be able to calculate that portion of the pitch increase that could be attributed to a .030" increase in bridge height.
>
> RN
> Yes I can, at least to reasonably illustrative rather than precisely predict. It requires specifying the starting pitch, speaking length, wire diameter(s), back scale length, overall bearing angle, and overall string length from tuning pin to hitch. I think that's everything except friction.
>
>
> Do you mean that if I supply this data, you will tell me the answer?
>
> DS
>
>
> By the way, is it possible to relate the 4% and 12%MC that you referred to earlier to relative humidity?
>
> RN
> Do you have a copy of the excel spreadsheet I offered a while back?
>
>
> No, I'm afraid I don't. Are you still offering it?
>
> DS
>
>
> I don't know...it just seems like you're saying something different. Can you explain?
>
> RN
> You want me to explain something you think seems to be something I don't see? Uh... no, I don't think I can.
>
>
> You choose to ridicule me here. You left out the quotes I felt were inconsistent. I'll repeat them:
>
>
>
> In response to me you wrote:
>
>
>
> 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.
>
>
> In response to Wim, you said:
>
>
>
> Wimblees:
>
>
> There has been a lot of discussion about tapping the pin to create better tone, less distortion, etc. But what are we doing? Is the better termination caused because by tapping we are driving the pin deeper into the wood at the bottom of the hole, thus creating a more stable pin,
>
> Ron N:
> Partly, but I think mostly dragging the string down with the pin to the notch edge.
>
>
> and
>
>
> WimB
>
>
> So what is the real reason for tapping? More wood, or less pin?
>
> RonN
> Or seating the string by proxy?
>
>
> You are telling me that you do not believe that tapping either the pin or the string will cure the lack of notch edge contact, but, in response to Wim, you at least imply that that is exactly what is being done. You may not be able to explain it, but you shouldn't place the responsibility for the confusion on me.
>
> DS
>
>
> Why DO you care about the string contact with the front edge of the bridge?
>
> RN
> Because when it doesn't, it eventually leads to tone production problems and false beats when the pin gets loose in the bridge. It's a practical consideration rather than a theoretical one.
>
>
> OK. So you feel that there is some increased likelihood of developing loose bridge pins when strings are elevated from the bridge surface at the pin. You imply either that the looseness would not develop, were the strings to remain firmly seated, or that loose pins would not be a problem with seated strings. What are the tone production problems, apart from false beats, that are eventually lead to?
>
>
> For clarity (for any other readers) I'm reinserting the portion of the following exchange that you deleted:
>
> RN
>
>
> Front bearing is the angle between the string segment on the bridge top and the speaking length segment.
>
> DS
> My contention is that, since the string segment on the bridge displays considerable curvature, it is misleading to think of angles or to assume that the imaginary straight line between front and rear bridge pin is meaningful in defining the angle actually formed by the two string segments as they converge at the front pin.
>
>
> RN
>
>
> I disagree. Poor front termination, with the accompanying tonal problems and false beats, becomes most problematical when the overall front bearing angle (that between the bridge top and speaking length) is very shallow. A strong positive front bearing angle DOES put the horizontal string termination on the notch edge and none of this stuff even comes up. It's only when that angle becomes shallow enough that the crushed notch edge no longer contacts the string. We've gone over the basic points a number of times reducing them to ever finer isolated details. In the piano, they all exist and interact at once, each in relation to other(s).
>
> DS
> Here's perhaps where we are still farther apart, and the fact that we've gone over basic points in ever finer detail should be viewed as purely positive achievement, in my opinion, not a source of exasperation.
>
> RN
> Did I say I was exasperated? The interrelationship is my point, and all these details have to tie back into the whole to make sense.
>
>
> You did not say you were exasperated, but I heard such in the italicized comment above (my italics - ds). Your response, beginning with "I disagree..." did not address my own previous comment, regarding my view of the profile of the bridge-string segments I commonly encounter. Of course it all works together, but insisting on viewing it all together when you are trying to understand the individual contributions makes no sense.
>
> DS
>
>
> I use a Lowell gauge, but as a determinant for front bearing, I measure the smallest possible segment behind the pin to compare with the sounding string segment. As it relates to termination, that's the only relevant part.
>
> RN
> I disagree.
>
>
> WHY?
>
> DS
>
>
> I also slide the gauge to the rear pin to observe the amount of curvature along that segment. It can range from .009" to .050", with the .030" range not being unusual.
>
> RN
> What's that in degrees? If you're using the rise per inch from the graduations on the Lowell gage, that's 0.003" per 10' of angle, isn't it? So you're telling me you measure anything from 0.5° to over 2.5°> of curve over bridge tops? Then again, holding a straight piece of wire in the groove in a bridge top, tangent to the curve of the groove at the notch edge, it will likely show more angle than that. I wouldn't consider this > to be a healthy bridge, but as you say, it's what we see the most of in the field. OK, now how could front bearing that never was over 2° produce a 2.5° or greater indentation?
>
>
> I don't know what you are asking, or why. I don't work with degrees. The exact measurement is irrelevant. Are you questioning my methodology or my accuracy in the actual measuring process? The numbers I indicated represent the differential measurements taken of the bridge-string segment with the gauge feet as close together as possible, first proximate to the front pin, then to the rear. They indicate a curved profile rather than the conceptualized straight line. There is no difference in the resulting bearing loading, but it does mean that, from a termination view, the immediate string segment behind the front pin is that part that will determine the presence of absence of positive front bearing.
>
> DS
>
>
> Second, I'm sorry to parse your usage, as you sometimes do mine, but you say no "significant sliding motion", which, of course, makes me wonder, just how much "insignificant" sliding motion IS taking place?
>
> RN
> I have no way to measure it precisely. When you do, please let me know. With inadequate pin angle and/or inadequate offset angle, I know the string does indeed slither up and down the pin. It sounds like a dobro on drugs, and is pretty hard to miss. And if I said NO motion, I would certainly be challenged to prove it. When I see and hear a piano with provably perfect string terminations, I'll have something by which to judge. Meanwhile, I'm attempting to get across what I consider to be reasonable, accurate and factual information pending something that makes more sense to me.
>
>
> I appreciate your efforts and your vision. (No strokes intended). You have challenge me innumerable times to be clear. That is all I'm asking of you. When, for example, you say that strings can indeed move on the pin if the various angles are not correctly executed, then, since we know that many of the pianos we confront in the field ARE less than perfect, it would stand to reason that the movement of the string at the (tight) pin COULD create some distortion that might be eliminated, temporarily by seating.
>
> DS
>
>
> Lastly, the analogy with the V bar is interesting but flawed. The offset angle of the string at the bridge pin is considerably less.
>
> RN
> How much angle difference constitutes "considerably"? At what point does "considerably" become significant? And I have certainly seen deflections across V bars that are similar to and even less than the horizontal offset across some bridges I've also seen. I think the analogy is quite valid and not that casually dismissed as flawed.
>
>
> Nothing about my communication with you is casual. I said:
> DS
>
>
> The offset angle of the string at the bridge pin is considerably less.
>
>
> I measured my Steinway O (1913). The V bar angle was 18 degrees. The bridge pin offset angle was 7 degrees. This seemed significant.
> DS
>
>
> The direction of string excitation is perpendicular to the V bar but parallel to the bridge pin. (If the hammer impact was proximate to a vertical termination, wouldn't you expect some string displacement?
>
>
> Whether it ultimately has any effect, I nevertheless see this as a significant enough difference in the modeling to have a potential impact.
>
> DS
>
>
> The direction of string excitation is perpendicular to the V bar but parallel to the bridge pin. (If the hammer impact was proximate to a vertical termination, wouldn't you expect some string displacement?
>
> RN
> Strings vibrate in all directions, not just in the vertical direction of initial excitation. You hear the tonal problems and false beats long after the string has migrated from it's purely vertical excursion path.
>
>
> I'll have to experiment, but it's possible that the non-false beat distortion we've been discussing is associated with the initial part of the tone, where the vertical mode is still predominant.>
>
> DS
>
>
> If you believe that the tightness of the pin in the bridge is the prime determinant of the presence or absence of false beats, why do you find negative front bearing unacceptable?
>
> RN
> Loose pins with low front bearing. Because pins don't stay tight forever, and I'd rather see the redundant support of both the notch edge and the pin at the same point with positive front bearing so there's enough friction between the string and the bridge top to keep even a loose pin from flag poling and making a beat. Wherever I can get one, I'd rather have a definite than a maybe. I've tuned a lot of pianos that sounded pretty good and acceptably clean in the humid summer months, but became un-tunable with false beats and other termination nasties in dry winter months. Pianos with tight pins and good crown and bearing don't tend to do this.
>
> I said the string doesn't "have" to be touching the bridge at the pin, and it doesn't to produce good tone, but it's more likely to produce good tone for a longer period if it does.
>
>
>
> I agree. I agree.
>
>
>
> David Skolnik
>
>
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