Permanent Soundboard Crown!

[Richard Brekne]

Indeed I do !

These guys claim RIB crowning leads to curveacouse permanence !... and 
here I thought you needed an operation to fix that trick. I like the 
disadvantages bit....   really.... a sheet of paper on a ball.... :)

Farrell wrote:

> Hey Ric, maybe you'll enjoy this one more - it goes even further - 
> from the Bluthner web site:
>
> /At the beginning of piano making the soundboard consisted solely of a 
> thin wooden board, stiffened with bars glued on the underside and the 
> bridges on the upper side. Further development was derived from the 
> soundboard of a violin with its spherical crown. However the 
> soundboard of a violin is made of a thick piece of wood being shaped 
> by grinding, chipping and sanding into its final form./
>
> / /
>
> /A piano soundboard is made from a thin board being bend by force into 
> this form. This method however produces disadvantages comparable to 
> those which one will experience when you try to put a sheet of paper 
> atop a ball./
>
> /Studies made by Bluthner research and development department have 
> proven that tensions and compressions develop on the edges that are 
> inhomogeneous and not controllable. In contrast, the soundboard that 
> Bluthner has developed has a cylindrical curvature so that the tension 
> of the soundboard can be exactly defined. The ribs are planed to fit 
> the curvature needed and therefore the tension of the soundboard 
> remains intact over the decades. In fact, even under difficult 
> climatic conditions the curvature will remain in a constant form since 
> not only the rib structure will hold it in place but also the red 
> beech inner rim is preformed to the correct angle to receive and 
> retain the soundboard's curve tension. Because the soundboard is 
> pre-stressed in this fashion it can be fitted exactly and _remain 
> under curve tension permanently._ The bridge, of course, is adapted to 
> the tension and curvature of the soundboard in its optimum position. 
> This ensures that string vibrations in their full spectrum are 
> transferred to the soundboard. By utilizing the resonating surface, 
> the special design of the Bluthner soundboard generates tone 
> significantly better. /
>
> Ok, new terms now. "Curve tension" - any engineers out there?
>
I think you can read tension as <<stress>>. They seem to use the word 
thus over here. Clearly they are not pre-stretching the thing and 
expecting it to survive the dry central european winters. :)  Looks to 
me like one on the rib crowned / beveled rim team. At least thats half 
way over in your camp !

Tho... if one first wanted to argue... one would mention that fully 
homogeneous and controllable stresses are not nearly the advantage as 
rib-crowned enthusiasts would have us believe. Especially when the cost 
is the reduction of internal compression so necessary to create that 
wonderfully CSB sound. Not that I can really pick sides mind you... I'm 
just a poor preachers kid from Montana :)

> Look that up in your old Engineering 101 book. Cylindrical curvature? 
> The top of their inner rim in not more-or-less planar (and the few 
> that put a slight rise in the concave curved side doesn't count)? And 
> somehow the angled inner rim retains the soundboard's curve tension! 
> Also, how does one go about adapting a bridge to tension and 
> curvature? The curvature I can roll with, but the tension? Who/what is 
> pulling where? Or maybe they are just pulling our leg?
>
> Fun thoughts.
>
> Terry Farrell
>