<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF"> Thanks for taking my confusions so well there Terry ! :) One comment to your comment... also interspersed below. Also... I am glad that we agree on the positive side to all this. It is a good mental exercise, and it is valuable to know how they might work for a lot of reasons. Farrell wrote: <blockquote TYPE=CITE><style></style> Hello Richard. I know some have express some disenchantment with your persistant theoretical explorations of soundboard crown, but I am rather enjoying it. It's a good mental excercise. And I also understand that even though you may well never build a soundboard, it is still a great thing to try and understand how they might work. There are not very many authoritative references available to find answers to these questions. So with that in mind, let's proceed to do the best job we can leading each other into an advanced state of total confusion............ Comments interspersed below: Terry Farrell <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">  Now if the rib is secured to the panel such that it bends a bit in the same direction as the panel, (i.e. glue say about 10 inches in on each side)  then the only thing that has really changed is that the rib bends upwards a bit... as in the below drawing. Yet the same basic condition exists. Downwards pressure in the panel increases the outwards pressure, yet this is resisted just in the same way as in the previous two examples, so in response both panel and rib will feel an increased stress and will strain against that stress until one of the pieces fail, which of course will be the panel. Keep in mind here that stress and stain, although related, are two very different things. Stress is a force that is applied to an object - or an object's ability to resist deformation. Stain is the deformation. With the soundboard, I suppose stress is delivered to both panel and rib, but strain is negligible for the rib, and orders of magnitude larger for the panel. I've searched for numbers that describe this relationship, but have found none.</blockquote> </blockquote> That's true... the rib will strain much less. And finding out how is pretty much a guessing game. I've heard a couple figures thrown out, very different from one another, and calculating with E maybe or maybe not gives a reliable figure... but just so... we know it has to experience the same stress as the panel, and it simply has to strain somewhat or it couldn't bend to begin with. Question then... is the support of crown a function of the strain of the components, or the stress, or both ? I mean.. I dont know this and I dont see this kind of construction dealt with anywhere in texts,  so there are no examples to go by. In any case... seems like there has to be some degree of strain on the ribs, and since their ability to resist strain is great, then just as great must be their ability to recover from that strain, and I end up in basically the same place. Then too... if you first do take for granted that the rib doesn't strain one iota... and so does nothing to support crown against down bearing.... then how can you explain the first drawing with the cable holding the panel crowned ? There's no way that you can say the cable is not supporting that assembly against down bearing... yes ?? No matter whether or not you try and analyze the cables strain or stress figures.. you just KNOW its supporting the system against down bearing. So where's the difference between the cable, the rib, and the rib glued a bit in from the ends, and finally fully glued to the panel ?? Its still doing primarily the same thing as the cable. It ends up doing some other things as well... but still... its holding the crown up, and will fight any pressure downwards on the panel. So anyway... :)... I dont seem to be able to get past this point with it... and if I am to accept that the ribs simply fight against crown in a CC board I have too.   <blockquote TYPE=CITE> <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">  But until that point is reached, the entire system will resist down bearing vigorously. No doubt the rib will straighten at some point, and the relative tension/compression on the top and bottom sides will equalize, but it will have to experience an increase in overall tension for this to happen, which it will resist. The panel will also straight out at somepoint... but nobody believes for one second that it wont be under stress when its flat.. So why should the rib be any different ? Opposite side of the same coin. Both will physically strain against the stress, the panel a good deal more then the ribs, but the stress levels are the same on both. <img SRC="cid:part1.3F9C05D3.E57DAC34@grieg.uib.no" height=319 width=506> The only thing that remains is to simply glue the entire rib to the soundboard, but I cant see that that changes anything. If the above three steps hold, then it seems in error to say that the only thing that supports crown in a CC board is compression in the panel. The entire system, panel and ribs alike will strain against down bearing. Ok... so this seems to make perfect sense to me, and though ribs are not acting as beams in their support, they can neither be said to be purely fighting crown. Quite the opposite. The fact that the rib is bent in the process, and of course resists this bending can be said about the soundboard as well. But I dont see that simple bending of either describes their condition adequately.  </blockquote> </blockquote> -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A> <A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>   </body> </html>