Ron Nossaman wrote: > >You are absolutely correct Ron ....... if you assume that the entire > >soundboard assembly is constrained from expanding as it takes crown. Such > >is not the case. >From Dels desciption of what happens to a "soundboard", both with and without ribs, when it is exposed to humidity after drying, it is quite obvious that the entire panel is constrained from growth. So there should really be no discussion on that point. > >If the assembly did not expand, then the ribs would be > >under NO tension and would be incapable of opposing the load exerted by the > >soundboard. If the ribs are under tension, they stretch, ergo the assembly > >does expand. No argurment here, and we are getting closer to the heart of the dissagreement, which I contend is more a matter of sematics and perspective then it is anything else. > Whether the entire panel is compressed depends on the relative > >sizes, geometry, and material properties of all components of the entire > >assembly. Hmmmm.....within the usual operating parameters of what a "soundboard" is, I kinda have to assume (with plenty of room in my back pocket for error) that this is a non-point. > > > > >Frank Weston > > > Ron N wrote: > So what? In a CC assembly, the ONLY reason it takes crown is that the panel > is constrained from expanding, on one side, by the ribs. Why would I not > assume constraint with panel expansion? Are the laws of physics going to > suddenly change arbitrarily? It's inevitable, unless the assembly is kept at > the drydown EMC forever, or not dried down at all, in which case you won't > get crown, or a working soundboard. Yea, obvious, and so what? I don't see > where pounding a point that's contrary to the way it's done, and won't > produce a working soundboard is going to get anyone anywhere. In a real > world situation, where the intent is to make a nominally functional > soundboard by the compression crowning process, the entire panel will be > under compression when the assembly is completed and brought to ambient EMC. I really dont see that Frank has said anything to the contrary of this. What he is saying is that there is another way of viewing the situation, one that is left out when one views the compression of the board only in terms of how much the panel would have expanded with out ribs, versus how much the ribbing inhibits this. If you substitute the terms "less compressed"(for the up side), "morecompressed" (for the bottom side) with the terms "tense" and "compressed", then Franks reasoning begins to become clear.Frank is saying that the top side of the board is "tense" relative to the bottom side, and since this is simply another way of saying it is less compressed (which everyone seems to be in aggreement with) there is nothing "incorrect" about it. In order to make that substitution you have to re-allign your viewpoint a bit. What Ron and Del describe is the situation relative to how much growth restriction the ribs enforce on the panel. However, if you take the dried panel, measure its dimensions, even go so far as to measure the distance between and size of the cells, then glue the ribs, subject it to humidity, and finnally load it in such a manner that the board is again flat... then the "origional" dimensions of the panel (dried) are restored. Viewing the panels size in terms of what it should be given the humidity will yeild the "doubly compressed" view that Ron and Del describe, and of course this is perfectly valid. However, viewing the panel size in terms of its "origional, dried" state (which you may or may not think is valid) yeilds a restoration of origional values and the panel is then at rest. In this second view one must then equate the forces acting upon the board as canceling each other out.. ie.. humidity vs download. In the first view, one must view the board as being doubly compressed because its "origional" state is in reality "the size of the unribbed unloaded panel at say 40% relative humidity" Applying this same thinking it is easy to see that the ribbed panel cannot achieve this same state of "equilibrium" given Franks "paradigm". I aint saying thats a bad thing.... that kind of a judgement is beyond me. The value I see in Franks view is that it lends itself to bringing this relationship to light, yet its weakness is that it neglects the fact that the board is indeed doubly compressed (panel size relative to humidity) as so easily shown by Dels and Rons model. So which board is best ??? beats me.. again I am just trying to follow along, look at the two opposing views and attempt to understand what each view is really "saying". Personally, I doubt that there is any data to support the claim that either is from a holistic point of view any better, tho from the point of load bearing it seems clear that the rib crown is stronger, especially in the long term. This however might be a "negligable" if climatic conditions for the finished piano are kept at an optimum. > > If you are talking about alternate realities, and soundboard assemblies that > are built with no intention of producing a working soundboard, I wish you > would say that up front and save everyone some time. I, at least, was > attempting to seriously discuss practical concerns and real world phenomena. This is the second time you have bordered (if not crossed) into the arena of personal slurs since I have been participating in this list. They do you no credit, are uneccessary, and annoying. I have no doubt at all that Frank is a very serious minded person indeed, carrying on a very serious minded debate. If one or the other "side" in this issue turns out to be the most "correct" way of viewing things, then hopefully those who are "wrong" will learn something in the course of time without the discomfort of such demeaning comments. > > > Ron N Ok... this was my attempt at "unifiying" to some degree the two standpoints. As I am just begginging to learn this side of pianos myself, I expect I have made a few mistakes. But not being one who is afraid of making a fool of myself (especially if I can learn something in the process) I submit it such as it is. So rip me apart, hopefully in an instructional fashion... .grin. Richard Brekne I.C.P.T.G. N.P.T.F. Bergen, Norway
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