rim supported soundboards tesnion resonator rods

[Richard Moody]

>But certainly if the rim did spread out a bit, it would tend to flatten the
>board. So I should think the rods would help maintain crown. Yes? No?

No.
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There is nothing preventing piano makers from using the rim to support a crown.
Whether it worked or not is another story.  Yet according to Dolge, the "Tension
Resonator" patents of Richard Gerz in 1900 were supposed to do just that.

"...the purport of which is to regulate the pressure in the arch of the
soundboard against the strings and to assist the vibratory efficiency of the
entire soundboard......    Another function of this resonator is to restore the
original arched form of the soundboard....[to]draw together the entire rim upon
which the soundboard is fastened, and force the latter back to its original
arched form, reinstating and enlivening the vibratory action of the entire
board. ...the tension rods can be screwed up, either simultaniously to bring
pressure upon the entire board, or individually if any part of the soundblard
should show a pronounced flatness.  They are furthermore of great value in
maintaining the correct form and shape of the rim.  This invention has been
applied to all the grand pianos made by Mason & Hamlin since the granting of the
patent. "
        (Alfred Dolge, Pianos and Their Makers. p110)

    I have heard considerable debate about what actually (if anything) was
accomplished by the rods.  Never the less if M&H did design a rim to support the
sound board arch the concept was at least given a try. The interesting part of
the debate to me is whether this is an efficacious way of maintaining the crown.
I am not sure anyone knows, unless they are/have actually used it.
    I wonder if makers have put soundboards by themselves in a room with
variable humidity and measured dimensional changes, the arch in
particular.  ---ric