Duplex

[Overs Pianos]

Dan Franklin wrote;

>Some years ago at my first PTG National. .  was a huge class by John Ford
>Senior . . a dispute I had with Big John on the
>question of bi chords.
>
>My point was : if you pull one side of a bi chord its bound to affect the
>tension and the pitch of the other side. John adamantly disputed this saying
>that the bearing points of the bridge pins, the agraffes, coils etc inhibited
>this consequence.

If you are referring here to two unison strings which are hitched via 
a single hitch pin then I'd say that John Ford was correct regarding 
the hitch pin. While the pull on one unison will indeed affect the 
rear duplex length of the same unison, the effect will not continue 
around the hitch pitch to the adjacent unison which is sharing the 
same hitch pin. Yes I know, I've heard many who dispute this also, 
but they are wrong provided that the string tension is not too 
different for the two unison strings concerned. Sure, if there's a 
huge tension difference there will be a tendency for the unison to 
pull around the hitch. But under normal scaling tension deviations, 
this is not an issue.

And before Dan feels tempted to remind me again of my proximity to 
kangaroos, I might mention that Del has also written posts to this 
list which concur with my view. I would also add for Dan's benefit 
that I do not employ Kangaroos, apart from the fact that they have 
difficulty holding tuning lever, they are dumb. I prefer not to 
employ idiots.

>  Now transferred to the question of the duplex which you raised, this seems
>to be a cogent point. . . I think you are probably right: that the 
>excitation of the
>speaking length activates the duplex around the "trees" of the bridge pins,
>hitch pins etc

"activates the duplex around the "trees" of the bridge pins" - nice 
line Dan. I agree with you that considerable energy gets over to the 
rear duplex from the speaking length. This is I suspect why some 
manufacturers set their rear duplex lengths to a semitone higher than 
the harmonic of the speaking length (I have seen this done in a 
couple of high-end Japanese pianos, where they actually did a 
remarkably good job of locating the rear duplex block assemblies). In 
doing this, they would seem to be setting the duplex length to the 
harmonic of the adjacent note to reduce the tendency for excessive 
string energy to transfer to the duplexes.

Ron O
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Website:  http://www.overspianos.com.au
Email:        mailto:ron@overspianos.com.au
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