[CAUT] Tuning the back duplex

[ibook]

On May 27, 2007, at 10:44 AM, Richard Brekne wrote:
Richard,
> Hi folks.
>
> I have been spending a lot of time lately playing with various  
> ideas in relation to the back duplex length.  I know there is a lot  
> of back and forth discussion about the viability of this idea...  
> but the following thoughts have prompted me to start looking closer  
> at this whole thing.

As have I.
>
> It has been stated time and time again here that the friction  
> levels needed to be overcome for a change in tension to occur for  
> this length are great enough that if true, one can assume that this  
> length would remain quite stable during play, perhaps more so by a  
> good deal then the speaking length. This would mean that any  
> (reasonable) pitch adjustment to  of these lengths could easily be  
> done during the course of a usual tuning. I find routinely that the  
> pitch of these lengths for unisons vary quite a bit and these  
> variant pitches remain stable from tuning to tuning. This allows  
> for quite a large window for which to tune these lengths to.

A very fruitful study.

>
> It strikes me as intuitively obvious that lengths of the same  
> length should have as identical pitches as possible.

This could require more study.

> In fact, it is quite easy to accomplish this with an ETD on the fly  
> as a part of a regular tuning. If you need to increase tension,  
> just use a string hook and pull on the speaking length close to the  
> bridge pin in a direction away from the pin....

I have made a string hook with a 1/2" arc and an approximate 3'  
radius to prevent kinking and your idea of polling away from the pin  
is very good.

> or simply tune the string quite high until the back length rises in  
> tension enough.

I have found that over pulling the string to raise residual tension  
can stress the string beyond breaking tension.

> To go the other way simply do the same on the duplex length. Fine  
> adjustment is easier then you might think. In fact the whole  
> process doesnt add all that much time to a regular tuning, and can  
> be expected to hold pretty darn solidly at least as long as the  
> next seasonal change. Climatic changes affect the whole darned  
> instrument so this is not a reason IMHO to not tune this section.
>
> Now...

True.

> just what is the most optimal frequency relationship to the  
> speaking length to tune these lengths too is another question.  I'm  
> getting the feeling that if one assures that the tension is higher  
> in the back length then the speaking length.... that you end up  
> with a cleaner sounding instrument.... but I am still  
> experimenting.  Any thoughts would be greatly appreciated

I have not tread lightly here but delight in joining a fine mind in a  
study in which many have indulged in passing as have I.
I find as have you that higher tension is favorable, variable  
tensions (read variable pitches) not commensurate with the series of  
the speaking length are not too noticeable, but any piano with  
tunable back lengths cannot stand perfectly tuned back lengths for  
the resulting stridency of the ringing after damping.

Again, my own experience indicates regular tuning process rarely can  
keep the residual tension higher than the speaking length and that  
higher tension on the back length could aid soundboard collapse.

Your contributions are greatly appreciated and look forward to a  
continuation of same.

Daniel Gurnee  HSU Ret.
>
> Cheers
> RicB