evaluating sdbd. crown & bridge downbearings in a new piano

[Delwin D Fandrich]

----- Original Message -----
From: Richard Moody <remoody@easnet.net>
To: <pianotech@ptg.org>
Sent: Wednesday, September 22, 1999 7:57 PM
Subject: Re: evaluating sdbd. crown & bridge downbearings in a new piano


>
>
> On the side of all this.. I have always wondered about something that
perhaps
> some of you can answer for me. What is "wrong" with the idea of "heat
shaping" a
> board into crown. Much like boatmakers apply heat and humidity to bend
planks,
> or for that matter as piano techs do to twist hammer shanks and the like?
Could
> not a soundboard be crowned and ribbing in this fashion ? Would it be
strong
> enough ??  Just curious.
>
> Richard Brekne

Heat shaping, or bending, alway weakens the wood to some extent.  (This is
also true of hammershanks, which is why the practice should be kept to a
minimum.)  Also, it is a difficult process to control.  Not to mention a
very time consuming one.



> Then it wouldn't be under "tension"  One of the ideas of crowning a sb is
because
> bent  wood seems to "amplify" the sound.   There used to be a
demonstration model
> consisting of a piece of soundboard between two pieces of wood with a
tuning fork
> mounted in the middle.  The blocks of wood could be screwed closer
together thus
> forcing the soundboard wood to bow.  When the fork was sounded on the
bowed board it
>  was much louder than sounding on the flat board. How much this really has
an effect
> in the piano is hard to determine, one of the considerations being the
board is
> bowed across the grain in the piano instead of with the grain as in the
model. Also
> if the piano sound board were bowed as much as the demonstration model, it
would
> probably have a two inch arch.  ---ric

Bent wood does not "amplify" sound.  Piano soundboards do not "amplify"
sound.  Piano soundboards do not amplify anything.  Ever.  Under any
circumstances.  They are not amplifiers.  They do not add any energy to the
sound.  They are simply transducers in the sense that they change energy
from one form to another.

The demonstration model using the tuning fork proves only that you can tune
the resonant frequency of a wood assembly by altering its stiffness.  And
that that particular soundboard operates very efficiently as a transducer
when its natural resonant frequency is tuned to the specific frequency of
the tuning fork.  That is what happens when the "crown" of this model is
altered -- its stiffness is being changed.  Which would be fine if the piano
had only one note.  Otherwise resonances within the soundboard panel can
only be considered to be voicing problems.

Del