Killer Octave & Pitch Raise

[Richard Brekne]

Arnold ! Takk og iligemåde !!

Thanks for this description of some of the alternative methods for 
dealing with some of the problems the design and construction of the 
soundboard is.  The "K" punkt that I've mentioned before is not in 
Fenners book as such eh ??  Well there certainly was some talk about it 
after/around his talk in Bergen a couple three years back at our 
convention here. But I can see I'm going to have to go back and get some 
more specifics about what was said and what wasnt. I appreciate any 
clarifications on the matter and yours seems to be the most thorough to 
date. 

Reading through your post there is one thing that strikes me that I 
thought I'd ask about. At the end you mention cooking a bridge, very 
dry, then glueing it to the (unribbed) panel to achieve crown.  I assume 
this means that the bridge shrinks along its length, and then when glued 
on wants to grow again. When the panel resists along the grain the whole 
unribbed assembly crowns (along the grain)  as a result of the strain 
between the panel and bridge.  Yes ??? Then as down bearing is added one 
sees additional compression along the grain.... yes ??

Interesting indeed and I wonder what implications this has for ribs 
strained by the compression of the panel across the grain.... tho no 
doubt the panels strength along the grain is far greater then its cross 
grain strength in this regard... still.. I've often wondered if the ribs 
to more then simply strain and bend  against the expansive stress placed 
on them by the panel.


Cheers
RicB



Richard mijn jongen

Thanks for the compliment and blowing my cover 
(you already know that I don't like you  that much 
:/))
/
I can see that it is somewhat confusing but I am 
only referring to the fact that the name K  isn't 
mentioned as such in Fenner 's book.
Steingraeber and Fenner  employ different crowning 
methods at least in the way of  the total amount 
of crown and where to put the highest point of the 
soundboard. The both use the cc method for their 
boards. When you talk to Udo Steingraeber he will 
emphasize that his company is not constructing the 
board the Fenner-way but uses a different 
approach. How that approach is in detail I don't 
know but I know they achieved good results. Now 
about the Fenner approach, at least as I perceive 
the method he describes is his book.
Fenner is (was) an advocate for using stress in 
the board as an effective possibility to change 
the different frequencies in the various areas of 
the board to get a better match with the string 
frequencies. The goal is to achieve an uneven 
stress in the board more towards the treble and 
less towards the bas. He is also talking about the 
bending stress along  the grain which is a 
effective way to raise the frequency analogous to 
a singing saw. Fenner constructs his boards 
following this principle and doesn't want a 
uniform crown but an uneven crown with more stress 
with a highest point shifted to the treble. In his 
book he explains how to do achieve this and 
calculate the radii for the ribs etc. which are 
used for the board and the mould.
To help achieving a shift in frequency bending the 
board along the grain will not help that much so 
he is compressing the board in  that direction. 
One possibility is (before gluing)to lift he board 
at the highest point with a  block temporary fixed 
to the braces about max. 2 times the expected 
crown and then fix the board to the rim. After 
gluing the block is removed and the board will 
have some extra compression. Or you can combine it 
with pressing  the board into the cavity of the 
outer rim which is more easily done before fixing 
the bridge to the board. Extra compression along 
the grain can also be achieved by gluing the long 
bridge (straight not curved) after the board is 
glued in. Yet another approach is to glue a 
heavily dried (cooked) bridge on the board first, 
before gluing the ribs to achieve a crown and add 
some extra stress.
So much for now

This  time a friendly salute

Arnold