Compression ridges was :Do you dry the ribs, along with the board, prior to gluing ?

[Ron Nossaman]

>>> Where's the analog in a piano if the bass 
> soundboard is stiff?
> 
> The analog is either the tapering of the panel near the edges, tapering the
> ribs near the rim, routing a groove around the perimeter, or floating it, or
> perhaps some other yet unknown process.
> 
> 
> Dean

All of which, unknown processes yet unnamed, is intended to 
make the bass more flexible, not  more stiff.

Give it up. The bass needs flexibility.
Ron N