"I think the reason they didn't use taller ribs is because with compression crowing, the taller, stiffer ribs won't bend under panel compression and you won't get adequate crown. Isn't it true that the narrower taller ribs that you see on some older pianos were generally radiused?" I would think this is reasonable speculation. The link I posted to the five lectures was intended to point out that there are more perspectives concerning ribs, their height, width and numbers then just how much load they are able to sustain. In addition to increasing the soundboards stiffness in general a second and very important consideration for rib dimensions is to compensate for the differences in bending stiffness parallel to and across the grain (anisotropism). In addition there is evidence to support the idea that wood under compression which does not exceed the elasticity limits of the wood in the direction of the applied compression actually can increase the stiffness of the panel itself. There are procedures today that take direct intent on effecting exactly this result. One such procedure is called Viscoelastic Thermal Compression, http://www.research.vt.edu/resmag/sciencecol/pressure.html which seeks to basically take advantage of the fact that there is a direct relationship between the stiffness of wood and its density. It basically increases the density of the wood without negatively effecting the strength of the wood cells in response to compression. It is plausible to wonder if it is possible to some degree over some period of time the CC board approach increases the stiffness of the wood perpendicular to the grain by virture of an increase in the panels density due to compression that is low enough not to exceed the elastic limits of the wood employed. If so, then the use of lower wider ribs need not take the same regard to this requirement as in a panel with little or no compression. Another point worth pondering is the difference of the distribution of such increase in stiffness over the panel as a whole might achieve. As for the quote above... indeed the empirical methods and means employed by our forefathers may have included stumbling upon an desirable acoustic effect from using taller ribs. Such ribs would indeed be more difficult for a compression panel to stress (bend) and so machine crowning these to some preconcieved radius may have been an attempt to get around that problem to some degree... ie allow for a compression panel with higher ribs that did not need as much stress for the assembly as a whole to achieve a given crown. Compression Crown had been seen by empirical means to on the short term increase in resistance to and increase in load until overloaded and failure occurs. No doubt the limits for this were emprically established and panels were kept within what were perceived as within tolerances. Speculating on what these fellows so long ago were thinking is a lot of fun. Earlier on there was a tendancy to align the grain so that it ran in the direction we run ribs today. Instruments of this sort were typically low tension affairs and downbearing forces correspondingly low. They also typically displayed very low rib height and often quite wide. This would allow for a good deal of compensation for bending stiffness using compression as the medium while not stressing the wood perpendicular to the grain so much as with stiffer ribs. At the same time the stiffness of the wood along the grain may have been seen as sufficient to handle what little downbearing force was applied on such panels. This is pure speculation on my part based on my limited understanding of all these issues... but it seems to make sense. And indeed the hybrid board that Terry and I contrived works very well indeed. I am convinced that if I had greater insights into more of the issues involved that this grain orientation along with a laminated crown and modest ribs would provide a very satisfactory alternative to the way things are done usually today. So called tunnel crown could be achieved with great strength, ribs could be contrived so as to satisfy anisotropic bending stiffness requirements and take less concern to load bearing requirements. Seems to me worth persuing. As do very low tension scales IMHO. I'm convinced that a very fine marriage between modern sound and the sound of straight strungs of old can be achieved at much lower general volumes using low tension scales. Cheers RicB
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