On Fri, 28 Dec 2001 09:31:26 Delwin D Fandrich wrote: > >----- Original Message ----- >From: "Phillip L Ford" <fordpiano@lycos.com> > >> To come somewhat to the point, >> I've been pondering whether rims should be massive or stiff or both and >why? > >I doubt anyone has done any exhaustive tests on this. I suspect the answer >lies in the basic mechanical impedance relationship, i.e., mass being more >critical toward the treble, stiffness being more critical toward the bass. I've heard you say this before and it's confused me every time. Perhaps I need a little more tutoring on this. I believe you want high impedance in the treble and low impedance in the bass. Is that correct? Isn't high impedance given by low mass and high stiffness and low impedance by the opposite? So I would think stiffness would be more critical in the treble and mass more critical in the bass. Or in other words, I would think you want to insure that you have a lot of stiffness in the treble and you have a lot of mass in the bass. Do I have this backwards? > >>> >> Should the mass and stiffness be uniform or should it vary and why? > >With a so-called 'continuous bent rim' it would be difficult, or at least >inconvenient, to vary mass from one end to the other. Granted. It does seem like a potentially good idea to have the rim thicker in the treble region and thinner in the bass region. Production would be an issue. > >As to why, the idea is to keep as much energy in the soundboard panel as >possible. A light and/or flexible rim will more readily absorb energy from >the soundboard, energy that would be better used in maintaining the sustain >time of the vibrating mechanism. Yes. This is the conventional wisdom that I have always accepted. Stephen B saying that some old makers deliberately made flexible rims made me give this another thought. I think this makes sense if rims really are less efficient at converting vibrations to sound waves than soundboards. On the surface of it this would seem to be true, but now I wonder at least a little bit. >Typically the loss of sustain time due to a low-mass, >low-stiffness rim is countered by making the soundboard thicker and the ribs >a bit stiffer. (Though ribs don't really have much effect on tone >performance through the last couple of octaves in the treble.) Why do you say that? Should the ribs be removed in this area? What then? Make the board a little thicker? > >I wouldn't necessarily say mass is inconsequential, but would question how >much mass is really required. Again, I doubt whether any tests have been >specifically devised to determine this. I've seen some pianos with very massive rims that I've assumed are overkill (especially since the particular pianos that I saw weren't great sounding pianos). Since the soundboard is flexible, it seems that at some point adding more mass or stiffness isn't really helping you since the rim is so much more rigid than the soundboard. This seems to be one of those areas like so many others in piano design - each maker settled on what he wanted but if he did some exhaustive testing to determine some ideal (or some point it was pointless to go beyond) he never let anyone know about it. Also, do you think that damping is a factor? If mass and stiffness alone were what was wanted then why not make the rim out of steel. I've seen numerous patents, and a couple of pianos, where the soundboard is attached to the plate or a metal frame that is attached to the plate. This idea doesn't seem to have caught on. I wonder if that was because of the sound quality, or for some other reasons. >> >> If the rim needs to be massive, then why? I've heard it said that it is >> 'to reflect waves' back into the soundboard. But I've also seen a few >posts lately >> that suggest that waves don't travel in the soundboard. > >If you don't like the idea of 'reflecting waves,' how about just not >absorbing energy. (Or has that been removed from the soundboard as well?) > That sounds OK to me. I don't really have a problem with reflecting waves but then I don't really know enough about it to know better. I was just tossing out comments I've heard here lately (or my take on them). >What little study and testing of this I've actually done indicates that the >rim tends to rotate around its center of gravity in response to the wave >energy moving the soundboard. And that center of gravity is typically below >the top of the inner rim. I'd not be devastated in finding this is wrong, >but I would be some surprised. With a clamped-edge vibrating panel the >tendency of the vibrating panel is to rotate the >clamping mechanism. >As far as the soundboard is concerned the top of the inner rim is the >critical area. I've thought about this before. From a structural standpoint it would make some sense to have the rim CG in the soundboard plane. This would seem to give the least movement of the soundboard perimeter for a given rim mass. > >We are used to building soundboard systems that go along with a particular >type of rim assembly and that is typically stiff and massive. Few of us, >unless specializing in replacing soundboards in pianos using Select Hardwood >rims, have much experience with low-mass, compliant rims. The pianos I've >seen using low-mass rims still use soundboards of the type used in pianos >using high-mass rims, they are just a bit thicker and stiffer. Personally, I >don't care much for the sound of those I've encountered. But that doesn't >mean soundboards can't be designed that will work better--at least 'better' >by my definition of piano tone--in these pianos. > >I've been giving some thought of late to various methods of reducing the >weight of the modern piano without sacrificing anything tonally. Building a >lighter rim is one way of doing this if the soundboard design can be >tailored accordingly. I take it you're not thinking of making the soundboard thicker and the hammers heavier. >Undercutting will not appreciably affect either the stiffness or the mass of >the rim assembly. Relative to the mass of the inner/outer rim assembly very >little wood is actually removed. The purpose of undercutting is to enlarge >the working soundboard area through the affected area. As to whether this is >advantageous or not is another issue. I'm not sure that we're talking about the same thing. What I was talking about was the relief in the rim that you describe for the Marshall Wendell (what I was calling a Chickering). This would seem to me to cause a reduction in rim stiffness that the soundboard sees. Mass might not be significantly affected. >> If you want soundboard flexibility is it a good idea to thin the rim as >some of the >> old makers did > >What do you mean by "thin the rim?" > >Del I'm not actually sure. I was referring to Stephen B's post about some old makers making the rim deliberately flexible. I assumed this meant making a light or smaller cross section rim or lightening the rim in certain areas (which might have been easier for them since they were working with solid rims). Phil F -- Click here for your very own create-a-date adventure from MatchMaker Go to http://ecard.matchmaker.com/dating.html
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