Soundboard crown

[Overs Pianos]

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>At 10:07 PM +0300 11/8/03, Calin Tantareanu wrote:
>. . . By the way, how do laminated soundboards behave when exposed 
>to humidity?
>Do they expand less than solid wood ones?

If you dry a quarter cut solid panel down to around 6% it will shrink 
about 3 mm in 900 (this will depend on the closeness of the growth 
rings, tighter grain shrinks less and vice versa). If you repeat the 
procedure with a laminated panel (with all laminates properly quarter 
cut and carefully joined as they should be also for a solid panel) 
you will have trouble measuring any shrinkage.

So for CC brigade, laminated panels cannot be used. Mind you, there 
is still a small shrinkage with the laminated panels, since we are 
finding that our 7.5 mm thick laminated tests panels are pushing the 
crown up about 0.5 to 1.0 mm once they are normalised after gluing. I 
don't really want any rise from panel compression but I feel the need 
to dry the panel just a bit, to provide a small insurance for 
extremely dry conditions.

I have been doing sound board deflection tests for the past two weeks 
straight. Amongst my findings, I have found that the typical modern 
sound board is so grossly overloaded in the killer octave region that 
there is little hope of such under-engineered sound boards ever 
giving a respectable service before the dreaded 'set' sets in.

Try your own quick test with a sample to see what I mean. Our rib no. 
11 on our 225 piano supports notes C52 to F#57, and has an active 
length of 580 mm. With just 1% of down bearing (which is quite 
moderate by current standards) this rib and panel strip will be 
subjected to a down force of 24.4 Kg. Build yourself a test rib of 
the contemporary-full-dimensioned sized of 25 X 25 mm (Steinway D mid 
board ribs), glue it to a 120 mm wide test panel and load it up on 
the bench with a 24 Kg test weight. You'll quickly realise why the 
typical piano's killer octave is well and truly dead before it 
arrives at the showroom. When you consider that most makers are using 
ribs smaller than 25 X 25 in the killer area, these will be subjected 
to even greater stresses. As an aside, I had occasion to take a look 
under a late Stuart concert piano a few weeks. The observed 20 X 21 
mm rib dimensions would seem, in the light of this discussion, to be 
an unusual approach.

Yes, I am working on a solution to this engineering disaster for the 
very next sound board.

Best to all,
Ron O.
-- 

OVERS PIANOS - SYDNEY
      Grand Piano Manufacturers
      _______________________

Web http://overspianos.com.au
mailto:ron@overspianos.com.au
      _______________________
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