RC vs CC again

[Farrell]

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So what about the high treble? Often the top octave or more is quite =
lively, loud and brilliant.

Terry Farrell
  ----- Original Message -----=20
  From: Marcel Carey=20
  To: Pianotech=20
  Sent: Sunday, October 05, 2003 5:49 PM
  Subject: RE: RC vs CC again


  Terry Farrell said:

     " When flat ribs are glued to a very dry flat panel, no force =
vectors exist in the system. As the panel takes on moisture and the ribs =
bend, the ribs will always be trying to pull the panel flat. Period. If =
that assembly has crown, the ribs will always try to go straight by =
pulling down on the panel. The compression forces in the panel are the =
only thing that has provided the force necessary to bend the rib into a =
crown. Whether or not you ever load that soundboard on top, the ribs =
will always be fighting the panel compression to go flat. When you do =
apply a load to the top of the soundboard, the compression on the panel =
will increase, but the ribs will do nothing other than still try to go =
flat. As the crown lessens under increasing load, the ribs will pull =
downward a bit less, but only because they are being bent upwards less =
by the panel. "=20

    The way I see it, the reason why we have the killer octave problem =
with mostly CC boards, is that the crown produced with the panel's =
growth will be kind of proportional to the lenght of the ribs. So, with =
this method the treble that always have shorter ribs than the tenor will =
have less crown in the beginning. Since compression will affect the =
board's with aging, we end up with a dead killer octave and a no crown =
zone exactly where the ribs get shorter...in the killer octave.

    So I guess there is no way to have a decent board assembly that will =
have a predictable lifespan with the Compression Crowned method. It's =
physics.

    Again, I might be wrong, but I think I've seen the light.

    Marcel Carey, RPT
    Sherbrooke, QC


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