Killer Octave & Pitch Raise

[David Love]

I didn't think that wood expanded and contracted very much along the
grain and that crowning took place due to the dimensional changes across
the grain. 

David Love
davidlovepianos@comcast.net 

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Richard Brekne
Sent: Friday, February 11, 2005 4:54 PM
To: Newtonburg
Subject: re: Killer Octave & Pitch Raise

 Udo Steingræber and I got into a conversation about this in Helsinki a 
couple years back on the only opportunity I've had to sit and chat with 
him.  It was part of a discussion where he was explaining why he felt 
compression soundboards were the way to go.  He mentioned something 
about the so called K point (I think this is a Klaus Fenner coined 
term), which as I understood it was that point on the soundboard where 
crown from both along the grain and cross the grain intersect and is at 
its highest point. This area is exactly (and always) in the area 
typically refered to by american techs as the <<killer octave>> area, 
and of course varies somewhat from piano to piano.  It is then  also the

exact point then that is most vunerable to failures.  Udo was of the 
position that along the grain crowning was every bit as important as 
cross grain crown.  Something to do with along the grain compression due

to downbearing having a stablizing effect on cross grain crown and 
strength.  He also meant that both these were needed to produce the kind

of acoustical results he wanted from a soundboard. 

I'm under the impression, correct me if I am wrong, that most of the rib

crowned methods extoled on this list do not employ any purposefull along

the grain crowning as part of how the panels are attached to the rim, 
and therefor do not have this vunerablity.  It would stand to reason 
that they too are not able to create the same acoustical  results.... 
(whether that is preferable or not is an entirely different subject).

Disclaimer.  This description is my understanding of what Udo was 
saying, tho I beleive it is pretty accurate. Not being a soundboard 
engineer tho, I'll leave it to more experienced to explain, interpret, 
or whathave you the above. 

One other thing tho... I've always heard that large changes in pitch, 
and destringing / restringing proceedures should be carefull of this 
area.... making carefull changes that are appliled very evenly,  exactly

because this area can easily be damaged by sudden large changes in the 
stresses applied to the panel as a whole.  Seems to jive well if the 
basic view above  is correct to begin with.

Cheers
RicB




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