More on soundboard crown

[Ron Nossaman]

>If the ribs provides no "positive spring resistance" then the panel 
>receives no support from the ribs and it would be no stiffer by having the 
>ribs attached. Yet this contradicts hands on experience. A panel crowned 
>soundboard is stiffer than just the panel itself. There is added stiffness 
>so it comes from somewhere. That somewhere has to be the ribs.

I didn't say the rib was independent of the panel, and a flat rib that is 
being forcibly bent upward by the panel isn't directly supplying lift. It's 
supplying leverage by constraint that keeps the panel under compression. 
The panel compression is supplying the lift, including fighting the rib's 
tendency to remain flat. So the rib constrains the bottom of the panel, and 
resists crown.


>Why don't you address the stiffness of laminated ribs?

They work the same way. The bottom layers supply the constraint under 
tension that keeps the top layers under compression. Just like a panel 
crowned soundboard. And just like a panel crowned board, the result is a 
stiff crowned assembly even though the component parts are all trying to go 
flat again. A solid rib works the same way, only it's parts aren't trying 
to go flat. The bottom half is under tension and the top half is under 
compression, producing stiffness under load. That's why beams get stiffer 
at the cube of their depth instead of at a one to one rate like it would be 
for cumulative fiber stiffness.


>O.K. I will say it again. If two or more soundboards have the same 
>dimensioned ribs and the same panel thickness and THE SAME CROWN at the 
>same EMC. Then the two Soundbaords assemblies will have the same stiffness 
>even if the method of crowning is not the same.

Again, I disagree. Given a panel crowned assembly with a severely dried 
panel, and one rib crowned with a non dried panel, both to identical crowns 
at room EMC, the one with the higher panel compression level will have the 
steeper spring rate gradient, and will be stiffer.


>>>There are many advantages to rib crowned soundboards (God knows we've 
>>>heard plenty)
>>
>>There sure are, and I think I recall hearing some from you. Don't you 
>>redesign Steinway soundboards with crowned ribs when you replace them?
>
>
>And your point being what?

It just sounded like a gripe, so I thought I'd remind you you're part 
source of the "God knows we've heard plenty".


>Maybe valid to your experience, not to mine. Are you calling me 
>unreasonable. You got to do better than that.

I thought your interpretations, assumptions and conclusions regarding the 
results of my misleading "theory" were unreasonable, yes.

Ron N