Soundboard tension & compression

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Richard Brekne=20
  To: Pianotech=20
  Sent: November 25, 2002 2:19 PM
  Subject: Re: Soundboard tension & compression


   =20

  Richard Brekne writes:=20

  And I just KNEW this was exactly where things were going to happen. I =
guess thats a positive sign anyways.. :) It seems obvious that all the =
confusion, or dissagreement, or whatever it is, is centered right at =
this exact bit here... the presumed tension in the outside of the panel. =
The confusion starts exactly the moment we release the assembly from the =
caul then. Until that point, everyone seems to be in aggreement that =
there in tension in ribs (panel side) and outside of the panel itself, =
and compression on the inside of the panel. =20

  What is not clear is WHY, (i.e. what the mechanisim is and how it =
works)  the tension in the ouside of the panel somehow reverses to =
compression when the panel is released from the caul. One is quite =
liable to think that whatever tension was there would simply be halved =
(assuming the assembly returns aproximately half way to its origional =
flat state). Actually, one could be tempted to think that this was the =
whole point of the process... to pre-tense as it were, the outside of =
the panel so it could take on crown without so much compression.  And if =
one DID assume that, then the rest of the logic that follows would seem =
to make perfect sense.=20

Well, Richard, it may not be clear to you but it is to many, if not most =
others. I should hope very few would actually tempted to believe that =
whatever exceedingly slight tension the top of the panel started out =
with would simply be halved. You're off considerably on the scale of the =
various movements involved. There must be compression -- quite a lot of =
it -- to hold the ribs in a crowned condition.

I keep telling you that it would do you some good for you to devise =
little experiments to illustrate these things but you seem some averse =
to this approach. So, I've done it for you. But the file is some 3.5 or =
MB large (there are a couple of pictures). If you're interested I'll =
send it on.=20

Regards,

Del


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