Sound Board Crown

[John W. McKone]

Ed Wrote:
>        You may want to measure the bearing at several places under the tape,
>before you move it up or down several ribs.  Doing it this way can give you
>an idea of the board's overall shape.
>
>       Amount?  Seems like all pianos have their own optimum about of bearing
>pressure.  It must be enough to tighten the whole structure, but not so much
>that the sound board has been forced to it's elastic limit.
>
>     I would be interested in how much downbearing others find appropriate
>for old soundboards; who does what?
>
>Regards,
>Ed Foote

I just HAVE to be a little nit-picker here, and point out the distinction
between bearing and crown...

Crown is the curvature of the board.  Which can be measured quite well
using the method Ed describes. (never thought of using tape leader - you
must do a lot of studio work Ed)

Bearing is the amount of string load on the bridges, measured as the degree
of string deflection over the bridge.

These two measurements are independant of each other.  A piano can have
lots of crown and no bearing, or lots of bearing and no crown, or lots of
crown and back bearing - but no front bearing. etc...

As to the point of the initial post.  I agree with the idea that its the
tone of the music that tells you if the set-up is OK.  An extreme example
is a Steinway B I came across a while ago that had serious negative bearing
(the strings were riding so high on the bridge pins that they could not be
seated) and a flat board - but it sounded GREAT! - not that I'm going to
set up my next rebuild that way or anything - but I'm not going to mess
with this one either.

Just getting back at Ed for correcting me on my non-traditional needling
post ; )

John McKone, RPT
St. louis Park, Minnesota
(612) 280-8375
mckonejw@skypoint.com