Ric: You mentioned Jim Ellis' article in the September 1982 Journal and offer to send it to people if you can get permission. Anyone can have a copy of that article if they purchase the 20 year Journal CD-rom which is available at https://www.ptg.org/store/product_info.php?cPath=22&products_id=44 dave David M. Porritt dporritt at smu.edu -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Ric Brekne Sent: Wednesday, September 13, 2006 4:47 AM To: pianotech at ptg.org Subject: Bridge Seating / food for thought -- a retraction Cy Shuster wrote: > Isn't it possible that when the string touches the pin above the bridge > its leverage makes for a less-secure termination, effectively increasing > the speaking length? Which is exactly what I've been saying repeatedly for, what, seven or eight years now? Since it's been published now by someone official, I suppose it might finally be taken seriously. Ron N Hi Folks. A few days back I responded to this by stating that this was not what had been forwarded here on pianotech in the past. That was perhaps a rather presumptious statement on my part which I would like to retract. My understanding of what had been said and explained was definitely at odds with the above. But my understanding of someones words do not necessarily represent what the respondent actually meant. I've had quite a bit of off list discussion going on about all this loose pin / recessed bridge theory for a good while now. My own perspectives has led me towards thinking along lines that the bridge termination as a whole being springy or massy is the determinant for whether false beats occur or not. I believe there are solid physics grounds for this. That said, these same discussions and the last exchange on pianotech has directed me to re-read many of Ron Nossamans postings on the subject and I believe at this point he is saying something very much along the same lines. That a recessed notch edge and loose bridge pin /contribute/ to the bridge termination becoming more springy then massy for the affected string I do not question. If that is what he (Ron N) has been trying to say then I agree, as far as that goes. Whether a loose pin and a recessed notch are in themselves enough to cause this anisotropy to the degree needed to enable a false beat remains perhaps in dispute. Its a very complicated picture to begin with and as I have said before... I can not find a statistical correlation between the two. This has led me to believe that there is more at work here. It also seems apparent to me that if a termination becomes a springy support...then it is not really a termination any longer. The "effective" point of termination would correspond very closely to the length of string necessary to cause the frequency difference for the applied tension. The fact that the pin is moving in phase with a string in a given vibrational direction then is evidence that it no longer is capable of fully terminating the string. Perhaps more correct would be to say it becomes effectively part of the lengthened string. It should also be noted that the amount of side movement needed for the pin to move in this scenario is the same (for all practical purposes) as the amplitude of the string vibration at that point for the *lengthened* string direction. This puts it in the microscopic range I believe and also relieves my concerns about what appeared to be claims of very large movements (wobble) on the part of the pin. I would like to point all interested to the September issue 1982 of the Journal. Jim Ellis has an article series there and has a particularly easy to understand analogy with a pendulum experiment that shows clearly the basic functioning of a springy vs massy support. Using the pendulum analogy.. if the support for the pendulum is springy, the pendulum will act as if it was longer then it actually is. The support itself <<swings>> in phase with the pendulum. As such it is no longer strictly speaking the fulcrum for the pendulum. That is moved up above the support and doesn't actually physically exist. If the supports are braced to prevent them from moving <<in concert>> so to speak with the pendulum, then the pendulums frequency will increase and its *effective* length shorten. The analogy to the piano string is obvious. There are several examples which show what happens with 2 and 3 pendulums (strings) attached and what happens when mass is coupled to the supports. Reading of this should make clear the mechanism at work that can cause a false beat if anisotropic localized boundary conditions at the bridge exist for any given string in significant enough degree. That is to say if the string sees the bridge as more springy (to large enough degree) in one vibrational direction then in another. Otherwise I would like to state unequivocally that I share the skepticism of many on this list towards aggressive string seating. I stand by my position that string seating is a necessary procedure to carry out, but only when a string (for whatever reasons) finds itself unseated in the face of a bridge whose entire surface is at or above the line of deflection for the string. Whether that can happen or not is another discussion entirely. I personally see no reason to doubt that it can. If anyone lacks the aforementioned article.. I will see if I can get it to you. I will of course have to ask permissions. Just email me off list. With hopes this can bring the subject matter further. RicB
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