[CAUT] Duplex angle

[Mark Cramer]

Hi Alan,

I'm actually looking for 15 degrees as a "minimum" and about 22 as a max.

This angle measured, at the capo, as an upward deviation from the plane of
the speaking length of the string.

Glue some card-stock onto the side of a small but square peice of wood (size
of a key-dip block, but only the width of a unison). The card should
protrude about 1/4" above the surface of the block.

Cut a generous "V" from the card to allow for the capo.

Starting at the capo "V" trace a line 15 degrees upward (or whatever your
parameters are) from the surface of the block onto the portion of card that
will stick up between the strings in the front duplex. (is this making sense
Alan?)

Any case, you will have a defelction guage you can reach into the action
cavity with, and press up against any unison to observe front-length
deflection.

i.e.: viewed from the side, the string will be parallel with your line, or
perhaps a little steeper.

I always find it interesting, no matter how it appears by eye, how nice a
job the staggered duplex bars do of keeping deflection fairly even from note
to note... as if by design. ;>)

best regards,
Mark Cramer,
Brandon University

PS Don't throw the block away just yet. My "permanent" one actually has a
plastic key-top (rather than card) as a  side "fence," and I use it to
ensure treble strings travel a straight line across the capo. With strings
de-tensioned, do a preliminary string-spacing by pushing the string sideways
til both string segments contact the fence parallel.



-----Original Message-----
From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org]On Behalf Of
Alan McCoy
Sent: Wednesday, November 08, 2006 3:21 PM
To: College and University Technicians <caut at ptg.org>
Subject: [CAUT] Duplex angle


Hello,

Point of clarification regarding "counterbearing angle."  I want to check
out an assumption of mine about this. When there has been discussion about
this on either list, some angle, for example 10-15 degree, is said to be in
the ballpark of what we are looking for. The question is which angle are we
referring to? The angle formed by the capo at the vertex, or the angle
formed by the counterbearing bar as the vertex?

These would be equal only if the speaking length and the length from tuning
pin to counterbearing are exactly parallel.

Of these it seems that the angle formed by the capo would control in part
the effectiveness of the string termination, i.e. preventing loss of string
energy into the duplex. Whereas, the angle formed by the counterbearing bar
would have more to do with tunability & tuning stability and also the tuning
or detuning of the duplex segment.

In a fully-strung instrument, how would I measure these different angles?

Thanks for you thoughts.

Alan

-- Alan McCoy, RPT
Eastern Washington University
amccoy at mail.ewu.edu
509-359-4627