v-bar/capo repair (filing compared)

[Ric Brekne]

Ric, is this shape supposed to offer more than an un-noisy duplex?   I think
I must have known at one time, but I can't remember now.

Barbara Richmond, RPT

Hi Barbara

The point of the sharp V shape capo is to provide a front termination 
that functions more as a pivot along the vibrational axis of the string, 
and less like a solid clamp which forces the string to handle the 
flexing at the termination internally. The more clamp like the 
termination the larger the increase in the strings stiffness and greater 
degree of internal friction waste.  On the other hand the more pivot 
like the termination the less stiffness there is. Stiffness gets into 
inharmonicity so the less stiffness there is the lower the inharmonicity 
( if memory serves me correctly).  The increase in efficiency provides 
for an increase in sustain and an increase in dynamic range. To quote Ed:

    "The pivot termination of the capo bar give the piano a greater
    dynamic range. Since the cap bar termination makes the string less
    stiff, the hammer can deflect the string more for a given blow then
    with a clamped termination. This is important in the treble, where
    the hammer strikepoint is near the capo bar and any increase in the
    hammers ability to deflect the treble strings will increase their
    dynamic range."

and

    "The profile of contour of the capo d'astro bar is important to the
    proper functioning of the pivot termination and the duplex system.
    If it is too broad and contacts the string along too great a portion
    of its length, it will negate much of the pivot termination effect,
    with several negative consequences for the tone quality and
    longevity of the strings.

    The ideal capo d'astro bar contour is a definite V shape with the
    contact point of the wire held to a 0.5 mm width. The angle of the V
    shape should be such that the string on either side of the capo
    d'astro bar is at no time able to vibrate into the bar. Keep in mind
    that the capo d'astro is not a U-bar, it is a V-bar; and it is not
    the grooves that buzz, it is the contour that lets the grooves buzz !"

and finally

    "The hardness of the material of the capo d'astro bar  also greatly
    affects the durability of strings. The material of the capo bar
    should be softer then the string itself, so that the string can self
    machine a rounded channel (approximately 1/4 of the strings diameter
    deep) on the 0.5 mm wide surface of the V-bar. "

Hope this helps a bit.  In short Ed claims, and I concur, that with a 
combination of a 0.5 mm V profile and appropriate degree of 
hardness/softness to the capo d'astro bar, you get an increase in 
sustain, clarity, and dynamic range and a reduction in the amount of 
string breakage.... and buzzing does not become a problem for many many 
years of even vigorous usage.

I've been doing this for quite a while now and it works every time.

Cheers
RicB


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