laminated ribs

[Erwinspiano at aol.com]

Ron---David
     Good discussion.  I've been  lurking in between sessions with the 
   Rah-chestah project.

Ron N wrote
> One question I have  is why, if you want to create a higher design loaded
> board, do you  need to increase the bearing?  On an RC&S board, with little
>  change in tone coming from modest changes in bearing, isn't it enough  to
> simply stiffen the assembly with the same residual bearing?   The difference
> would be, I assume, the amount of deflection.   But if the panel deflects 
30%
> instead of 50% is that a problem  tonally?  Wouldn't you have the same net
> tonal effect without  having to increase the actual bearing load on the
> board?   
My question is how  does that relate to the sweet spot I believe exists for 
crown  compression, bearing & tone in a belly system.  Being that the  system 
is a spring, the question for all Soundboard designers?redesigner is how  stiff 
is stiff enough for the type of tone desired & it's subsequent life  span. 


It  might. Design load isn't my concept, and isn't where I 
start with design.  My intent isn't to accommodate a higher or 
lower  design load, but to  provide adequate bearing that, if 
the board sinks out somewhat over the  years, there will still 
be adequate bearing left. Same with crown, to  maintain the 
opposing spring system of string and soundboard even with  some 
long term settling. I'd like to think that as well as sounding  
good to me now, they won't end up with a zero bearing negative 
crown  killer octave some day, and will sound good to me for a 
very long  time.
  Oh well said.  This is every bodies  dilemma but I am comforted by the fact 
that we have the history of 150 years or  more of data  to judge how well the 
compression crowned board have held  up.......or not. In some climates 
they've held up very well structurally &  where they have tonally as well. 
     That being said none of us( I  think none) are using straight sugar pine 
ribs  with a MOE   less than Spruce. SO we know that track record.  SO now 
enter boards  which are rib crowned spruce with  higher beam strength especially 
 with a tight grained spruce, laminated rib structure or Over I beam & we are 
 concerned that the crown, bearing & tone won't hold up?  Ron have  faith 
man. They will hold up.
  There is also a larger issue that we have been  tip toeing around & so I 
will say it. The tonal envelope on many of these  boards to my ears and others 
is a new & uniquely wonderful sound and  may be judged  superior by many to 
many compression crowned  systems. 
  (I have noted the tonal clarity by simply  switching to all spruce ribs.)
    Hopefully the tone crown &  bearing will  prove to having superior 
longevity as  well

Time  will eventually tell, one way or another, 
but that's one of the factors  I consider. This stuff is still 
relatively new to me, and I don't  pretend to know the details 
of all possible combinations, which is why I  continue to 
explore and learn. In five years, I may still be loading them  
like this, or I may not, depending on what I've learned in the 
  An honest man.  We are all on that  learning curve


interim.

Part of the equation in determining all this is  beam 
clearance, which puts limits on rib depth, crown radius, and  
loading. You pick your set of ranges for variables, juggle as 
you  think will take you farther in the direction you want to 
go, and prove or  disprove the hypothesis by stringing the 
sucker up and hearing how you  did. I'd love it if someone 
threw large quantities of money at me to  explore this stuff 
systematically in much greater detail at higher speed,  but I'm 
a one man shop with a tuning clientele, with the need to make  
a living in there somewhere. Otherwise, I'd be fearless. I 
hate it  when necessity interferes with fun, ya know?
   You empericalist.  Great self  effacing post!!!!!
   Dale



Bummer.

Ron N

 
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