>If I may try to answer my own question having read back through this >thread. The stiffness of the panel is produced by applying whatever >downbearing is required to achieve it. Stiffness of the assembly is increased by deflection of the crown by downbearing. >The difference being that the >ribs take the stress of supporting the bearing over time rather than the >panel and therefore the stiffness of the panel is likely to hold up for >longer avoiding the inevitable compression set if the panel were >supporting the bearing alone. Correct. The assembly will work more dependably for longer when it isn't reliant on high panel compression levels to work. >OK. So do you then have to compress the RC&S panel more to achieve the >same stiffness as the CC panel because the CC panel has a bit of a head >start, as it were? No, because you aren't relying solely on panel compression for that stiffness increase. You can make the ribs as stiff or as flexible as you like to build in whatever spring rate you think you want with the RC&S assembly. In the RC&S assembly, you can also easily produce considerably different spring rates in different parts of the scale. >And just how flat can you squash the RC&S board before you run the risk >of a problem, assuming you think you might need to squash it flat in >order to achieve a desired tonal quality. > >David Love There is no reason I know of that you can't squash it dead flat without problems (bearing angles and back scale lengths within reason). There are plenty of purely CC soundboards out there that are pushed flat by bearing that are still stiff enough to perform their function, for now, and you could do the same to a RC&S assembly if you liked. I prefer some residual crown under load, if for no other reason than that a combination of bearing and crown gives me an easily measured indication of how the structure is holding up. Whatever the residual crown under bearing, and whatever the construction method, if the assembly is stiff enough under it's bearing load, it will work. The RC&S board is just expected to work more predictably when it's built, and for a longer time in service because the material stresses are better distributed. Ron N
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