Moped10 wrote:so with a wound, instead of octaves, it'd just be a duplicate? (sorry if that's a dumb question, I'm a 12 string newbie)
For example, in a stock RIC 12-string set, the unison G is a 20 wound and the octave G is a 10 plain. That means the core of the wound string is in the neighborhood of a 10 (you could always unwind one and measure it, but for this purpose assume it is close enough), and so whatever pitch the string is tuned to, whether e or the octave g (the same diameter string is used for both in a RIC 12-string set, as well as octave D), it will have similar compensation. The winding is added for only one reason: to get the lower pitch, because for any given tension, more mass (larger diameter string) means lower pitch. But intonation at the saddle is usually a function of core stretch. So...the wound unison string with the core being about a 10 will need just about the same compensation as the plain 10 by itself, even though it is an octave down in pitch due to the windings. The windings, from a bridge saddle compensation point of view, are really nothing more than a slinky toy wrapped around the plain core with no significant linear stretch compared to the core.
Look also at the carved pre-compensated notches in a fixed bridge classic archtop jazz guitar. These guitars, to support a big band, used medium to heavy strings, and had wound G strings. So the notches on the bridge are usually something like this, as are 320/325 bridges, including the retrofit "bow-tie" bridge w/ Bigsby when using the stock 12-52-gauge set or similar, which also has a wound G string:
e|
b
||
g|
d
||
a
|||
e
||||
Conversely, guitars which use light gauge strings with a solid or plain G usually have their saddles set something like this:
e|
b
||
g
|||
d
||
a
|||
e
||||
You can see that the solid or plain G requires more compensation because the greater the diameter of the core, the more it goes sharp, and so the farther back the saddle has to be. By this, you can also see that any 12-string set that uses a plain string for both the unison and octave will not intonate on a single saddle, but a wound unison/plain octave pair usually will.
Tangent: the octave low E string is usually wound, instead of plain like the other octave strings, and this can have its own issues of intonation as well. I use a custom gauged set I assemble myself based on 9's, and so I purchased a blank bridge saddle and custom filed an offset saddle for the low E string, with the unison intonating off the rear edge of the saddle and the octave string (both wound) intonating off the front edge of the saddle, and both strings intonate correctly and are in tune with each other up the neck.
Attached: picture of a "bow-tie" bridge as used on Bigsby conversions of 325's which use 12-52-gauge strings with a wound 3rd G string in the same orientation as the text above:
