I wasn't suggesting you take off strings and poke around. The point was simply to illustrate that impedance characteristics are higher near the rim as you've pointed out. Is that what I want? Well maybe. We should probably clarify what we are talking about though. I was referring to the high treble in terms of the bridge centering question. The killer octave problems (lower in the scale) that you mention are low impedance problems, not high impedance problems and for the most part the bridge that corresponds to notes C5 - C6 (generally thought of as the killer octave section) is largely centered over the ribs. Less so at C6 but pretty much in the middle at C5 if you use the location on the rib as the reference point. Could this area benefit from higher impedance? I think generally it could. I'm sure you would agree. Higher up the proximity of the bridge to the rim can, as you mention, shift the problem to one of high impedance. Many pianos that have killer octave problems don't have problems in the highest capo section, at least not the same problem. In many pianos with killer octave problems the very top of the piano can sound just fine. On conventional designs the need for excessive use of lacquer is, in my experience, more a function of a poor or too soft hammer than too high impedance. On many pianos with firmer hammers that area is getting voiced down, not up. While you are correct that one could simply create a different rib cross section to capture the necessary impedance characteristics were the bridge more centered it's not the same. If you take load bearing characteristics in mind when you design rib scales, as I know you do, then you know that when you load the rib nearer the rim it's effective stiffness and load bearing capacity is increased. Short of differences in how the ribs are feathered, you will need a less stiff rib to perform the same load bearing function as the load point moves away from the center. You don't have parity there. The level of impedance that came from the bridge's proximity to the rim has been replaced by a heavier rib scale. The acoustic characteristics of a bridge nearer the rim with a smaller rib cross section may be quite different than a center loaded rib with a larger rib cross section. Not having attempted a side by side comparison I can't say exactly how that difference would manifest itself and centering the bridge at the very top of the piano because o strike point issues (at least on a grand) presents its own logistical problems. Just for clarification, my considering off center bridges is simply to understand better what off center really does. On the surface off center sounds bad, I mean, isn't everything that's "centered" better? Well I don't know. Just as you mentioned in your other post about the bass corner moving out of phase with the rest of the board. Well that sounds like a bad thing. We don't think of out of phase as having anything positive to contribute. Yet sometimes tuners will tune two strings just slightly out of phase to enhance the sense of sustain and bloom in a note. So is a soundboard that moves out of phase with itself a bad thing? Or is it something that can add a bit of life to the overall tonal envelope and how it develops? If so, how does a centered bridge contribute or detract from that that and therefore is it something that we really want. Symmetry isn't always a good thing. That's what's at the heart of my question and having experimented with several design iterations exploring these issues it remains a question. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Delwin D Fandrich Sent: Thursday, May 24, 2012 8:08 AM To: pianotech at ptg.org Subject: Re: [pianotech] David Love--Centering the bridge--was S&S something er other When I was designing the piano it seemed like a good idea. So my "experiment" involved actually designing and building a piano with the bridge located quite close to the center of the ribs. I was quite pleased with the results. Since I was/am already quite familiar with the results obtained with off-center bridges and here I had the results of one that was nicely centered that-to my ear, at least-performed some better I'm not sure how much more I would learn by taking the strings off one of these pianos and poking around with a tuning fork. Of course the proximity of the bridges relative to the rim (or soundboard liners) makes a difference in how it responds to the vibrating energy of the strings. All other factors being equal the impedance seen by the bridge will be higher the closer it is placed to the rim, but is this what you really want? The closer the bridge is placed toward the rim the more it's mobility is restricted as is seen at the high treble in hundreds of thousands of pianos of all sizes and at the low bass of small pianos. Is the performance of all those pianos with this design feature all that admirable? Not to my ear, it isn't. Nor, apparently, is it to many other ears; if it were we wouldn't see all the discussions about tone problems through the "killer octave" and about struggling to get good performance out of the high treble without lacquering the beejeebers out of the hammers. This is, after all, one of the design features of traditional grand piano design; the bridges are significantly off-center through roughly the upper third of the scale. In my case, by placing the bridge closer to the center of the ribs I was able to avoid these problems and achieve what seemed to me, at least, superior performance. One can, of course, argue that there were/are many other factors at work here and they would be right. Still, after having the experience of building my own piano with this bridge placement were I able to repeat the experience I'd put the bridge right back toward the center of the ribs. Nothing I've seen, heard or read has provided anything like a convincing argument to consider doing otherwise. If your only reason for considering off-center placement of the bridges is to control impedances I would suggest that manipulating the cross-section of the ribs would be a better approach. By using whatever combination of width and height you want the soundboard assembly can be made as flexible or as stiff as you want it to be while still keeping the bridge relatively centered and giving it the mobility it needs while still controlling spurious resonances. ddf Delwin D Fandrich Piano Design & Fabrication 6939 Foothill Court SW, Olympia, Washington 98512 USA Phone 360.515.0119 - Cell 360.388.6525 del at fandrichpiano.com <mailto:del at fandrichpiano.com> - ddfandrich at gmail.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Thursday, May 24, 2012 7:22 AM To: pianotech at ptg.org Subject: Re: [pianotech] David Love--Centering the bridge--was S&S something er other First, I do know better than to argue "better or worse" and that's not where I was headed. And you may be right about the issue of proximity to the rim versus centerline location. However, since this question I asked was prompted by a discussion of how to get the high end of the treble bridge more "centered" as if that was desirable, the question is relevant. Do a simple experiment, take a tuning fork and strike it and place it in the center of a soundboard (unstrung piano will be easier) and time how long until the sound dissipates. Then do the same thing and place the fork nearer to the rim. I think you'll find that it takes longer but do it for yourself. The impedance characteristics (the rate of energy transfer) is impacted by the location of the energy input with respect to the rim. Since a centered bridge is as far from the rim as possible whatever the width of the piano at that section one has to assume that the energy will flow through the system and dissipate more quickly the more centered the bridge is. With respect to the high treble where sustain is something that is sought after (by some) seeking to center the bridge may not be desirable and may, in fact, be undesirable. With respect to the lower end of the piano you certainly want it farther away from the rim for reasons mentioned. For those who have built transition bridges and located those bridges more toward the center of the piano (as in the old three bridge systems), you know that you can encounter impedance problems unless you add support and structure to the transition bridge and even then there can be problems. So proximity to the rim certainly can make a difference not just in how sections might blend but in the overall quality of the sound as it is impacted by the differences in impedance. Since the impedance characteristics impact the relationship between the attack and sustain phases, an important consideration in targeting piano tone, I think it's worth asking whether or not the location of the bridge on a soundboard makes a difference. I don't know how to answer it exactly but then if I did I wouldn't be posing the question. There are, will be, other differences to be sure. A wider soundboard will likely have a different rib scale, for example. A larger area soundboard will also tend to produce a lower frequency when you pound on it. Does that lower frequency have an impact on the character of the initial percussive attack? To my ear it seems to but I can't be sure that's that actual source of the difference. A general philosophy of "make no assumptions" has a benefit in that it challenges us to question the way things were done in the past. But if one is being faithful to that philosophy, it should also bring into question the practices we find ourselves engaging in by virtue of having challenged those old assumptions in the first place. David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20120524/c4d7c7db/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC