Increasing Crown

[Michael Spalding]

William,

I'm a relative newcomer compared to others who I hope will join in to
clarify or refute.  My perspective is that of a mechanical engineer turned
piano technician.  But as I see it, crown is a means, not an end.  In other
words, what you need from a soundboard is appropriate
stiffness/mass/impedence that endures for the life of the piano. ( Refer to
archives about impedence matching SB stiffness to string wt/frequency in
the different regions of the SB.)  Crown is a construction feature which,
in combination with traditional materials and design features, tends to
produce the desired effect.  There are other ways to achieve this,
including Del's epoxy surface coating.  I have noticed, in my brief career,
big improvements in treble power, clarity, and sustain in small pianos,
without doing anything about crown.  What you do have to do:  re-attach
separated ribs, shim or fill SB cracks, cap or epoxy the bridges, install
new bridge pins, re-surface the v-bar and agraffes.  Control your shop
humidity at the lower end of the normal seasonal range.  Trying to put
crown back into an old board by radically drying before shimming, or
pushing up on the underside before shimming, only ensures that during next
summer's high humidity the soundboard will compress and crush, and the
following winter the cracks will come back.  Bottom line:  if you want more
crown, install a new board and/or new ribs.  If you want to increase the
stiffness of the existing board, try the epoxy surface treatment.  If you
want noticeable improvement with low risk, do the basics with precise
attention to detail.

JMHO

Mike

> [Original Message]
> From: William R. Monroe <pianotech@a440piano.net>
> To: Pianotech <pianotech@ptg.org>
> Date: 3/13/2005 7:42:17 AM
> Subject: Increasing Crown
>
> List,
>
> I am currently working on rebuilding my own little piano to gain some
> experience, and have a question about improving the crown, function of the
> soundboard.  I had heard of shimming up the SB from underneath, prior to
> shimming, or doing anything else on top (Bridge repairs, etc.), in hope
that
> by doing these repairs while the board was shimmed up, they might act to
> improve the crown, even a very little bit.
>
> My question is about flowing epoxy over the surface of the board, as was
> discussed here a while back, and I'm wondering what you all think about
> having the board wedged up & flowing on epoxy.  My concern is about what
may
> happen when the wedges are removed - cracked epoxy?!?!?
>
> What say you?
>
> William R. Monroe
>
>
>
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