Wound Trichords

[Carl Meyer]

When rescaling, I typically increase the exposed core of the notes just
above the bass break to increase the inharmonicity (to fit the curve) when
small enough wrap is not available.  Typically No. 39 is the smallest
available.  I've gradually increased up to 28 mm on those above the bass
break if I have as many as 6 notes.  Even numbers are needed usually and it
also depends on the hitch pin layout.  I've never had any problem doubling
up strings on hitch pins, but you may have to add pins.

The calculating technician has some guidelines on exposed cores.

Carl Meyer Ptg assoc
Santa Clara, Ca.




----- Original Message ----- 
From: "Ron Nossaman" <rnossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, November 20, 2004 10:17 AM
Subject: Re: Wound Trichords


>
> >I had actually been thinking one way to improve the tone of the last
> >couple notes at the low end of the long bridge on my M&H 50 -- C#3, the
> >lowest before the break, is 38-3/4" long -- would be to replace the plain
> >wires with wound ones.  Now it seems mayybe I am full of misconceptions
> >and this is a bad idea -- but why?
> >
> >Trent Lesher
>
>
> Not a bad idea so much as a less than ideal fix. Putting the wrapped
> bichords on the low end of the tenor bridge will likely make it less bad,
> if it can be made to fit into the scale. For instance, that 38.75" C#-3
> with plain wire trichord will be at about 24% of breaking tension
> (regardless of wire size, within reason). That's pretty low, and will be
> very reactive to tension changes resulting from humidity fluctuations,
> meaning it will go out of tune quicker and farther than unisons farther
> up-scale, or down scale in the high bass. Tension will be determined by
the
> wire size used there. For instance, unison tension with #20 will be about
> 404 lbs, or about 369 lbs with #19. Going to a bichord unison, dropping
two
> or three half sizes for the core, and figuring wrap to get back near the
> unison tension that was originally there will raise the break% to around
> 40%. That's going to be a more stabile unison with humidity changes, and
> sound better too. The trouble is, that puts you at the bottom of the list
> of available copper wrap sizes, requiring about a 0.007" wrap to keep the
> tension down around where it was with the plain strings. Arledge uses as
> small as 0.006" for copper wrap. That takes care of C#-3, if the impedance
> and inharmonicity connects reasonably with the high bass. Now you'll
> probably want to go 2-4 notes higher with wrapped bichords to blend the
> impedance and inharmonicity into the rest of the treble. What happens? You
> maybe need 0.006" wrap for D-3, and smaller than is available for the next
> one or three. There's the problem, and the reason this doesn't always work
> that well, and the reason for transition bridges. The speaking lengths are
> too long at that pitch for wrapped strings. What you can get away with
> depends on the individual scale and what you have to work with.
>
> Ron N
>
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