More on soundboard crown

[John Hartman]

Ron,

You clarified you position on this just fine. Let me be clear about the 
way I see it.

There is practicly no difference between the two methods of soundboard 
building viewed from the perspective of mechanical performance. If they 
have the same dimensioned parts they will have about the same stiffness 
and mass. Therefor they will have the about the same acoustical 
performance. acoustical performance being dictated by these two factors.

Panel crowning puts the panel into more compression than rib crowning. I 
estimate this to be at most about 30% of maximum psi of side grain 
compression if building a soundboard with average dimensioned ribs. 
Panel crowning requires that the ribs be glued on at a lower moisture 
content than rib crowning. These two factors increase stress on the 
panel. This stress is regrettable but only a fraction of the amount of 
stress any type of soundboard with a solid wood panel will have to 
endure with seasonal changes in humidity.

Advantages of rib crowning soundboards:

Somewhat less stress on the soundboard panel.
allows for the use of heavier ribs if you are so inclined.
More controllable results.

Myths about panel crowning.

The ribs don't contribute to soundboard stiffness (unless all of the 
crown is gone. in this theory the soundboard become stiffer when it is 
flat).

The ribbing process uses all of the available compression of the panel 
causing the soundboard to immediately collapse.

Myths about rib crowning:

Improved tonal performance.

Impervious to loss of crown due to swings in humidity.

A new and improved technique (it was described in a late 19nth century 
text on piano building).

That's all I have to say on this topic unless something strikes me as 
off like your description of negative stiffness. I will let you get the 
last words in on this topic. I know you will, you have a lot more riding 
on this than I do.



John Hartman RPT

John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
Rebuilding Steinway and Mason & Hamlin
Grand Pianos Since 1979

Piano Technicians Journal
Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]