A440A@AOL.COM wrote: > Ron writes: > >How can a longer support area for a given load, on a given > >footprint width, result in accelerated wear of the support? This is contrary > >to logic as I know it. How does this work? Let's backtrack and plug a few > >holes before we hotly dispute anything else, what do you say? > > I have the same questions here as Ron does. Plus a few other things. > Inre the "damping" differences between the materials: I tried to answer that as best I could in my last reply. So I will wait for counters to go forward with that. > > When there is, in a vibrating system, something that damps as profoundly > as the soundboard, I don't know that the plate's contribution will make a > lot of difference in the damping. It would seem more important that the > plate be designed so that it has no audible resonant frequency (all > structures have one). Lack of audible resonant period shouldn't be confused > with damping, imho. I am not sure as to whether or not we are talking about two different things with regard to internal damping of cast iron. On the one hand, we seem to all have gotten past this buisness of Plate Ring, and I think there is aggreement there. On the other hand there is this more spread out effect reported by some if not many that describe a metallic contribution or coloring of the overall sound picture any given piano has. I personally have no trouble accepting this as both a possibility and a probability, tho in deference to the fine arguments and questions on the other side of this fence, I draw no definitive conclusion (besides, not being a metalurgist, acoustics PhD, and in general an outright genuis, I would be foolish to do otherwise.. grin) > > The increase in radius of the V-bar doesn't seem to cause any accelerated > wear, in my experience. The heaviest grooving I have seen has been on the > smallest radii. My experience is a bit different I am afraid. I do experience significant grooving in any system. But the deepest and widest grooving I see is on Brass U-bars. (typical on Schimmel upright pianos amoung others). But the groove itself is not the point, rather it is the contour of the termination point that allows the groves to become problematic (ie buzzing, brashiness etc). Here we are back to the difference between how a string behaves under the conditions of a pivot point visa vi the clamped point. There is also the buisness of string fatigue, and the ability of the string to sustain its vibrations. Again I will quote from Ed's book. "Even if no buzzes are present, the sustaining quality of the tone will be inhibited right from the start if the string contact area is too broad, since the pivot effect of the termination is inhibited. This will cause the wire to fatigue prematurely since it is forced to bend instead of flex at the forward termination point. The angle formed between the string and the profile of the capo bar should be a minimum of 20 degrees and a maximum of 40-50 degrees. What is essential is that the vibrating string not buzz against the sides of the capo bar. > > I also question whether the longitudinal waves that occur in a vibrating > string cause the string to move back and forth over the v-bar, since in so > doing, the tension would equalize ,and I know that I leave more tension in > the top string than in the speaking length, and that this tension > differential remains until the next time I move the pin. Is that not where > stability comes from? I am not sure where we got into longitudinal waves. I thought it was pretty much accepted that there are forces at work on a vibrating string over a clamped termination that allow for more then one direction of vibration over that point, whereas a pivot termination provides a way of (to no small degree) determining the vibrational axis of the string. I believe I ran into a web side at one of these universities who have lots of acoustics / physics outlines online for their students which displayed this in terms of the physics involved. I will look around and see if I can find it again. As far as stability is concerned, I would have to think that stability can only be served, not hindered by a pivot termination, to say nothing of the matter of inharmonicity. The strings stiffness is increased by a clamped point. This in turn causes the string to flex internally at the termination point which leads to some degree of internal friction within the wire. Then there is the matter of friction due to an increase in contact area with the broad termination point. While it may help to some small degree holding a slight difference in tension between the speaking length and the non speaking length from affecting a unison, it also makes moving the string into proper tension more difficult to begin with. > > Ron has some questions here that I would like to see definitively > answered, too. Grin... In all humbleness gentlemen, I am but an egg ferverently reading through what written material is available to me on the subject matter, and reporting what I find as it relates to your questions. Ed's book seems to anticipate many of these questions and objections. Tho there are no hard physics contained therein to back up his point. He has studied physics to some end so I assume he knows enough to know when he's out on a limb. Otherwise I can only say that what little I have found and been able to understand of this on the nett has only lent support to his descriptions. > > Regards, > Ed Foote
This PTG archive page provided courtesy of Moy Piano Service, LLC