Soundboard Evaluation

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Richard Brekne=20
  To: pianotech@ptg.org=20
  Sent: June 16, 2001 6:48 AM
  Subject: Re: Soundboard Evaluation


  Ok Del.. lets see if I understand the essence of the points in your =
reply correctly then...=20
  You saying the following..??=20

  1:  Compression crowning a board is basically synonymous with or at =
least necessitates "fiber compression damage"=20

Almost. I wouldn't use the word 'necessitates.' It's a result. =
Compression-crowning a piano soundboard assembly inevitably results in =
some amount of fiber compression damage within the soundboard panel.=20



  2:  Fiber compression damage will probably have little effect, if any, =
on the panels performance as a diaphragm in a rib crowned sound board =
assembly.=20

The best evidence to date points in this direction. It is certainly =
consistent with the theory of the rib-crowned soundboard system.



  3:  It is not the compression damage per se that causes the loss of =
tone performance, it is the loss of crown in the sound board assembly =
(the loss of stiffness) that results from that compression damage that =
causes the loss of tone performance.=20

Yes.=20



  4 The across grain compression strength  that maintains crown in =
compression crowned boards is inherently weak and will dissipate over =
time. (relatively short ??) (regardless of such factors like such as =
climate ??)=20

Yes. It is both time and stress dependent. The more compression stress =
the wood fibers are under, the faster the resulting compression-set will =
occur. The longer the wood fibers are under compression, the more they =
will be permanently deformed.=20

This is climate dependent to the degree that during dry periods moisture =
will be drawn from the wood fibers and the panel's internal compression =
will decrease. During humid periods the wood fibers will absorb =
moisture, try to swell, and the panel's internal compression will =
increase.=20



  I am not quite sure why a compression board is said to be "damaged" =
(fiber compression damage) when in essence this damage is meaningless in =
as much as all one has to do is re-rib and reconfigure for a rib crowned =
assembly.=20

Because, in essence, the wood fibers end up being permanently damaged! =
And that's meaningful. As this damage occurs, the performance of the =
soundboard--in its original configuration--is permanently altered; crown =
dissipates, string bearing decreases, and tone performance diminishes.=20

Is it meaningless that compression damage--and the resulting loss of =
tone performance--can start showing up in pianos that are only five and =
ten years old? Is it meaningless that soundboard compression damage can =
even be found in pianos while they are still on the showroom floor?=20

I'd hazard a guess the owners of these pianos don't consider it =
meaningless as their piano's tone performance gradually--sometimes not =
so gradually--dies and who are now faced with some rather expensive =
choices to get it back.=20

Finally, it probably not meaningless to the technician/rebuilder who =
will be taking on the task of remanufacturing the piano to give it a =
voice once again. That we can take the fiber-damaged panel, and by =
installing a rib system of a different design, make it functional once =
again as a piano soundboard is a whole other issue.

No, on the whole I'd say fiber compression damage occurring within the =
soundboard panel is anything but meaningless.

Del


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