On 5/13/2012 5:39 AM, David Nereson wrote:
> <<Neither demonstrates anything related to actual pianos and how
> they work.>> Maybe not, but the difference in tone between the
> relaxed (non-"crowned") board and the arched ("crowned") board while
> the fork was vibrating was definitely noticeable, even striking.
Yes it is, but that still doesn't make it a demo of how soundboards work
in pianos.
> But since this isn't related to real pianos, what's the purpose of
> crown again?
Since you missed this the last time I wrote it, here it is again.
> Crown, per se, isn't necessary to soundboard function. Crown in a
> compression crowned board as is used by Steinway is an artifact of
> high panel compression bending flat ribs up into a curve when the
> panel rehydrates. The ribs are actually resisting the formation and
> maintenance of crown. Loading this panel with string bearing pushes
> the crown flatter, and makes the assembly stiffer as the panel
> compression level reaches it's physical limit. The stiffness is what
> you're after. Given enough stiffness built into the assembly, crown
> isn't needed. Stiffness can be achieved with crowned ribs, acting as
> support beams, but the ribs need to be considerably stiffer than
> those in a compression crowned board to support string bearing with
> measurable positive crown without high panel compression levels.
>On the same subject (I think), what is the correct answer to
> clients who ask what makes pianos go out of tune?
Techs can't agree on anything, so why try to go into detail with
customers? Wood changes dimension over time under stress and with
humidity changes. Strings change dimension immediately with changes in
heat. Time, and changes in heat and humidity make pianos go out of tune
- whether they're played or not.
Ron N
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