jim ialeggio wrote: > Please remember that the following refers to an _rc&s board only._ This is a first, and absolutely critical realization. The "rules" are different from any (even partially) panel supported system. > 1- deflection of an individual stand alone rib unattached to any bridge > structure is quite linear and conforms to the deflection formulae. Yes, as is easily demonstrated, at least for a single rib. > 2- the addition of the bridge adds significant stiffness to the > structure. This was not intuitive for me. The bridge not only evens > (bridges) the loads, but it actually adds stiffness to the rib assembly. I wasn't aware of that, and still don't see why it would. > 3- the addition of the board and glue down to the rim adds stiffness to > the system Demonstrably, but I'd not try to calculate it into the mix. It's a freebie boost away from the edge of not being stiff enough, which you've already experienced. Being used to seeing ribs in panel compression supported soundboards, it's difficult to realize at first how very far away you are from too stiff with the new stiffer rib scale design. > 4-There are stiffness losses (though not from compression set as in > compression boards) related to beam relaxation and initial beam > springback(after ribs are removed from the laminating caul) Some, yes. The closer you get to stiff enough, the less obvious that becomes. > 5-***a biggy*** the deflection of the entire system, > ribs/bridge/board/rim, still behaves in a relatively > linear fashion (remembering that my experiment refers only to an rc&s > board, not a compression board). Which by the way explains why rc&s > structures are not as picky about downbearing as compression boards Correct^2. A big biggy. This is why I've said that pre-loading to set bearing doesn't work with these systems. They're too stiff in the unloaded state, and don't stiffen drastically as they're loaded, as does a high panel compression assembly. It's a different system. > 6- ***the punch line*** the load that each rib is expected to carry can > be mathematically be described as a coordinate point in a trend. If that > sounds like greek to you, open up an excel file, enter 2 columns worth > of x and y coordinates, click on the graph wizard, and graph those > points as an x.y scatterpoint plot. Then add a "trendline" to the plot > (this is all accessible through excel wizards). There are a bunch of > trendline choices, play with the polynomial trends and see what they do > to your plot points. Second order seems pretty close to the actual system response. I use this for calculated load distribution, and both initial crown height and loaded crown height. > The big thing I learned from these experiments was that anything we see > happening structurally or tonally will be observed as a trend; ie, a > tendency for things to go a certain way under a certain set of > circumstances. and to progress in an "even" or rather "trended" > fashion. Look for a "tendency" as opposed to a recipe. Exactly, or rather - generally. <G> This is one of the toughest concepts to absorb and nearly impossible to get across to someone else until they burn the time and brain cells necessary to see it. Everyone wants one linear checklist method, filling in the boxes sequentially with high precision numbers, which in turn automatically generate more higher precision numbers which, at the end of the checklist, produce the optimal no fault soundboard. Just gotta follow the checklist. But it doesn't work that way The tools and basic concepts are, though fairly simple, tough to assimilate in their interactions. And though collectively, they make a rather majestic sort of sense in how everything eventually fits together, you can't really distill any one detail down to an absolute. Owning a hammer, however shiny, still means you have to learn how to drive a nail with it. Good post Jim. You've got the basic pieces of the kit. Ron N
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