[pianotech] Tuning the duplex sections

[Joe DeFazio]

> From: Ron Nossaman <rnossaman at cox.net>
> Date: March 12, 2011 4:35:45 PM EST
>>> 
> 
> It will also be more prone to being noisy. A 15° counter bearing on a 20mm front duplex allows plenty of flexibility for this rocking motion (which is what's responsible for pretty much all speaking length energy in the front duplex), with no "clamping" at the capo, and no duplex Banshees. Even at excessively high counter bearing angles, the string still rocks across the V bar, even with as short a duplex as you can realistically get. Take a string hook to a string just forward of the bridge pin, pulling it sideways to tighten the string on the pin. You can see the segment on the bridge top between pins bow as you pull and the string rocks around the pin.
> 
> Go back to the front duplex, even on something like an Aeolian M&H BB, with a 45° counter bearing. Lift the damper, and pluck the front duplex. The pitch of the tone you will hear is that of the speaking length. The displacement of the front duplex when you plucked it pivots the string across the V bar and levers the speaking length into action.
> 
> 
>> In other words, the string cut might flare a little on
>> both ends of the cut. Has anyone ever noticed such?
> 
> Not obviously. Any flare would be almost entirely on the speaking length side. The excursion of the duplex segment is very small.
> Ron N

Thanks, Ron.  Good observations as always.  

I did pull up on the speaking length quite hard with a stringing hook while keeping a finger on the front duplex adjacent to the capo.  I was not able to feel the rocking motion.  Ditto with pushing down on the speaking length adjacent to the capo.  So,  the excursion must be quite small.  Now, of course, I have a string to level ;-)

Joe DeFazio
Pittsburgh


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