duplex bars

[David Love]

Del:

To continue an ongoing discussion, I have some questions re your article in 
the PTJ August 1995.  I am restringing a ca 1978 SS Model B.  One of the 
problems is that it is very noisy in the capo section.  I believe this 
problem can be traced in part to the capo bar being poorly shaped, which I 
will remedy.  However, I am also concerned about the shape/position of the 
duplex bars.  After rereading your article it occurs to me that some of the 
noise problems may be due to the poor shape of the duplex bars (they are 
very flattened), possibly the angle (though I have yet to measure it), and 
the position (a tuned duplex).

My questions are:

1.  Is there a method to relocating the cast duplex bars and would you 
recommend it?  There is a small shelf in the plate forward of the existing 
duplex bars.  Would you consider attaching an inverted V-shaped piece of 
something (brass?) in order to shorten the duplex segment?  If so, what 
would you use and how would you attach it?  How would you calculate the 
position, i.e., what should the length of the duplex be as a ratio of the 
speaking length?

2.  Is there a method to reshaping the duplex bars (I am not pulling the 
plate on this particular job), or would you consider adding a small bronze 
half round to the top of the existing duplex which would both give a smaller 
radius and increase the string deflection angle?  If so, do you still adhere 
to a maximum deflection angle of 18-20 degrees?  How would you attach the 
half-round?  And what specific material would you use?

3.  Do you think these things are likely to improve this problem, or should 
I be barking up another tree (pun intended)?

Thanks

David Love
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