Soundboardcrown

[Farrell]

Ron. I think what Peter is doing here is inducing a small amount of crown by gluing a flat rib to a flat panel in a curved caul at ambient RH. And of course, this will produce a small amount of crown. He then dries the board down and glues in into the piano. It would appear that he is relying on the rigid-rim-supporting-the-crown theory to keep the board crowned after it expands a bit with the increased RH. Obviously, there are a few of us that do not feel that theory holds much water, let alone crown.

Perhaps a tension resonator is needed?

Different folks will read the same things and come up with radically different understandings.

Terry Farrell
  
----- Original Message ----- 
From: "Peter Kestens" <peter.kestens2@pandora.be>
To: "'Pianotech'" <pianotech@ptg.org>
Sent: Tuesday, December 17, 2002 12:53 PM
Subject: RE: Soundboardcrown


> > Peter,
> >  From your description, I wouldn't expect your board to have 
> > done anything 
> > else but go flat when you dried it. 
> 
> I do not say and don't have said the board was going flat by drying it.
> I only eye-checked it and saw that some crown has disappeared compare
> whith the crown the board gets when it comes out of the press.  I don't
> have checked it with a straight piece of wood.  It was just by eye.
> 
> I really doubted it to dry it before gluing on the ribs;  but because
> I've placed last year a new bord in a Bechstein (no, I did not made it
> myself) and because I did not have much crown either with that board and
> because this piano sounded really very nice, (believe me I'm not the
> only one who's saying this and who have heard it sounding) I've not done
> it.  I dried this soundboard also before gluing it in the piano, for the
> reason you can read one alinea down.
> 
> >Why would you dry it to 
> > glue it in the 
> > piano when you apparently didn't to glue on the ribs? I don't 
> > understand.  
> It is not that difficult to understand.    When you dry it, it became
> flat  to place it in the piano; when it's done, because of the higher
> humidity of the environment, it has to swell, ie taking an arc because
> it can't move freely anymore due to the glue.
> 
> > As Del said, I hope you can get the ribs off without 
> > destroying the panel 
> > so you can start over again. In the four years or so that 
> > you've posted to 
> > the list, at least a month's worth of reading has been posted 
> > on soundboard 
> > crowning methods and expected results. Please go back and 
> > read some of this 
> > stuff, particularly the differences between rib crowning and panel 
> > (compression) crowning.
> 
> Believe me, I do understand it (Just for explanation: I've read and
> studied the compilation of articles published in the Journal the PTG has
> done concerning soundboards).
> Rib crowning helps you getting more consistant soundboardcrown for a
> longer period of time, but for the sound, using either crowned or flat
> ribs does not change anything to the sound, as far as I know.  I only
> know that using compression crowning needs more force to bend ribs and
> board and, I have to say, I hope that using this method gives more
> strenght and stiffnes to the ribs (ie, soundboard).  Isn't this the
> ultimate goal?  Please do correct me if I'm wrong.