Down-Bearing for Old Board /AND YET MORE!

[Erwinpiano]

Terry
  I do appreciate having to clarify this because it is a complicated subject
I think of all the time and has taken seemingly eons to digest .  Good
question . The really important underlying   "Jist ot the matter" is that
uneven pressure creates uneven impedance qualities. Thats Bad. For example
and I've expierienced this on many pianos new and old .  Certain notes are
louder than others or sing longer and these notes are right next to each
other.  It could also be a group of notes, frequently it is in octave 4 f
thru b.  One give away sound is kind of a thwacking sound. The  quick
irritating attack then weak sustain.O.K. can't voice it out either , maybe
camoflouge.
      This is a result of impedance problems caused by loss of crown and or
most often (in my opinion speak up my brothers)an non uniform setting of
bearing slash string pressure. I.E  How do I know this great mystery? Cause
I've induced this condition myself  on my own newly made  boards in my pre
nonstressing of the board days . I did fix the condition by resetting the
bearing and the anomally went away. It's only my opinion but many new pianos
are not set up with enough bearing which has been born out thru restinging
and resetting bearing on several makes of asian pianos.
   Until you do this a few times I can see why "you might be inclined to
think  that the amount the board is prestressed is a big assumption" but
here in lies the proof.  When rightly done it sounds wonderful and the
fearless bubble gauge will testify a very uniform reading thru the majority
of the piano ,has been set . The risidual values as measured will be in the
12 to 15 thous,range or slightly higher or lower.. And higher in the last
treble lower in the bottom tenor (cause you made it that way) and then the
bass ,oooohh I can't go there now but much less ?  The beauty of this system
is that  it is possible to set up very favorable bearing requirements
without being a rocket scientist .   And , each board , with practice can
kind of tell you how much to pre-load ( That and some good ole folridian
common sense.   Use of the infamous Kansas staightedge is a very helpful
diagnostic tool.  Thanks Ron N.   By the way you answer this one, how much
bearing does a  flat board need /get.  After all many flat boards(or Worse)
are restrung every day in America.
            One last teaser .   The bearing is not really set uniformly at
all! There is proportionately more pressure as you leave the tenor and head
for the top of the piano even though the gaposis  measured at the tenor
string rests seem larger  .    Hey ,but it's designed  that way to meet the
specific impedance needs of the treble and each of the sections  . Also
pre-stressing  provides for adequate amounts of bearing over the life of the
piano and its ever shrinking crown. shrinking crown shrinking bearing.
Really it's a very workable system .  Consider yourself armed and dangerous!
    From the west coast chapter of rebuilders anonymous
   President and founding member
  Dale Erwin