Killer Octave & Pitch Raise

[Arnold Duin]

Hallo Richard,

 >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 ??

Sharp as ever, your are right that is the general idea. I think he also 
mentioned that after gluing the bridge to board the moisture content of 
the bridge was lowered to the same level  as the board prior to gluing 
the ribs.


>I've often wondered if the ribs to more then simply strain and bend 
>against the expansive stress placed on them by the panel.

If you want to achieve as much as stress a possible in a soundboard you 
also want the ribs to be stressed and that will contribute to the 
concept that you will get the best (fastest) sound transmission when 
the material is under stress.


greetings
Arnold


----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Newtonburg" <pianotech@ptg.org>
Sent: Sunday, February 13, 2005 11:21 PM
Subject: Killer Octave & Pitch Raise


C 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. c
>
> 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
>
>
>
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