Jon explains the "dual-range guitar":
There are two strings for playing bass, four for guitar. Separate pickups generate signals for each, so each can be processed and amplified appropriately. I usually use fingerpicks. The tuning is (low to high):
||same pitch as the 2 middle strings on a bass
|D||}||the top 4 strings of a standard guitar tuning|
My instruments have an extension on the fingerboard that adds 2 frets on the lowest string, so that it goes down to G (49Hz).
I’m also experimenting with a 7-string version, which has the same bass arrangement, but the top five strings from a standard guitar.
This sort of thing is not unprecedented. (The godfather of fingerboard multitasking, Chet Atkins, also experimented with separate pickups for the bass strings.) But I think the design of this configuration and the way it can be used justify giving it its own moniker. If nothing else, it's good to have a short answer to the frequently asked "what the heck is that?".
Unlike a baritone guitar, the dual-range guitar does not transpose a standard guitar to a lower register, but instead stretches the range. Seven- and eight-string guitars also extend the range, but the approach here is different because the objective is to play basslines and guitar parts simultaneously.
Why? Are bass players that hard to find? My interest in doing this stems from a desire to have the same ability a piano player has to sketch out an entire arrangement from a single instrument. Originally I thought it would be useful just as an arranging tool, but I soon found that the instrument had a unique voice. Or rather, that the discipline of harmonizing the bass and guitar at all times encourages a unique style – in both composition and performance. Sometimes I think of it as a cousin of “chord-melody” guitar technique, but here it’s “bass-melody”.
One of the cool things about the 6-string version is that most familiar chord fingerings work with very little adaptation. A folk guitar E chord formation still works. And the A chord formation is still good – you just have to lay off the low D string (thumb & fingerpicks help). So you could use the instrument to become a one-man punk band. But that's not what I'm after. And I'm not much of a travis picker either – though someone who plays that style would probably have a blast with this thing.
I like to have the bass and guitar move in harmony or counterpoint. Having to economize – and to purposefully shift attention from motion in the bass to melody on the guitar – winds up being a benefit. You get a sound that's more coordinated than bass and guitar played by two separate people is likely to be.
And I've always liked to subtract anything that doesn’t specifically contribute to the effect the music is trying to evoke. I like harmony that’s parsed and distributed among all the instruments, with no one thoughtlessly sounding a bunch of redundant chord tones. The dual-range guitar facilitates that parsing.