<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF"> Delwin D Fandrich wrote: <blockquote TYPE=CITE> <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">Natural crown is an older English (British) term which seems to rougly equate your term Compresson Crowning. Junghanns text discerns between straight ribs on a flat panel, vs a panel pressed into a dished caul. In both cases we are talking about a thoroughly dried board, ribs across the grain. And in both cases crown is achieved by allowing the finished glued assembly to take on moisture. Where he notes differences are 1) The dish cauled assembly will immediatly become stressed when released from the call, where as the flat panel will not. 2) An asymetrical spherical curvature which is desirable can be easily achieved with the dished cauled assembly and practically impossible with the flat panel. 3 The crown achieved with the dish cauled assembly will be stronger and more stable then with the flat pannel. 4 The dish cauled assembly is more sensitive to being over stressed by too much downbearing.</blockquote> <div dir="ltr">I would take issue with #3 and #4. Assuming the ribs start out flat and are not machine crowned in any way, ultimately both are compression-crowned and depend on the ability of the wood fibers to resist the force of compression. It doesn't matter if the force comes from having been pressed in a dished caul or from taking on moisture after having been dried to some very low moisture. It is still compression and the wood cell structure reacts the same way.</div>  </blockquote> Yes, but isnt there some initial cross grain compression in the panel and tension in the ribs fresh out of the caul (dished caul variant) ? I mean why else would the panel assume an initial crown before it takes on humidity if not because the ribs are trying to restraighten themselves but are prevented in doing so. It would seem if this is the case that both issues # 3 and # 4 would be true then, tho it would also seem that this would increase the likelyhood of exceeding what compression levels the wood can handle when downbearing is added into the picture... no ?   <blockquote TYPE=CITE> <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">"As todays manufacturing is hardly able to use such changed of humidity deliberatly, this methods seems no to promise success. However, the authors (Junghanns (I guess)) seems to be different as he says the following. <blockquote>"An equal radius of the rounding of all ribs is desirable. If this is not achieved then the finished assembly will be under unequal stresses, a condition that should be avoided at all costs."</blockquote> </blockquote> <div dir=ltr>And all that trouble I go through to create all those unequal stresses ... what shall I do? But I do understand the theory. It is based, I think, on the notion that the response characteristic of the soundboard should be uniform across its span, or surface. At the risk of starting the Great Soundboard War all over again, if you will consider the soundboard as a series of overlapping loudspeaker drivers you will see why this is not desirable. You need a tweeter in the treble and a woofer in the bass. Their response characteristics are not -- should not be -- similar.  </div> </blockquote> An interesting picture I havent picked up on before,.. tweeter in the base and woofer in the treble. For what its worth there is a small quote from Junghann in this lecture that goes to this speaker analogy. He says...   <blockquote><< A good soundboard should have similiar resonance characteristics over the entire range from 27 to 6000 Hz. This would result in a panel with similar characteristics to that of a loudspeaker membrane. However, a loudspeaker membrane is subjected to an even and steady force from the electromagnet, whereas the soundboard is subjected to short impluses from the hammers impact with the strings >></blockquote> <blockquote TYPE=CITE> <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">Fenner goes on to say then that Junghann further states that for this same reason the bridge had to be fitted to the crown of the soundboard, and that this is contadictory to what is found in older texts, and he (Fenner, I believe) agrees with the older texts.</blockquote> <div dir=ltr>And my bridges will still go on flat.</div>  Del </blockquote> Well, as I read this... that leaves you and Fenner in aggreement on that point.   Cheers RicB -- 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>   </body> </html>