Here's my first double guitar design. I find that the bottom neck, for chords playing, would be easier to have 7 strings. The 7th string I tune to low B (same concept as normal 7 string guitar). This B string helped me a lot for alternating bass line playing with my left hand (almost similar left hand position like normal guitar playing).
I faced an initial problem with headstock design. The gap of the necks' pretty close, it's imposible to put 3+3 kind of machine head tuning. So I designed the inner 3 of the machine head with classical type as the pegs face downward instead of sideward.
At that time I couldn't find any simple fixed bridge for 7 string, I turned up using a "Floyd Rose like" bridge. And to make it consistent, i used the same type of bridge for the top neck too. Could you imagine how heavy this guitar was? ;p
At the end the weight's unbearable, it's so heavy just to stand up slinging the guitar. I changed the bridges with "Tune-o-matic" bridge like we always see at Les Paul guitar. Of course the cavities must be mended and put on some veneer to cover the scar on the body.
There's alwasy an open string's sound after releasing my finger from the desired note, so I used Spider capos (adjustable leg for every string) with some rubber material to dampen the open strings' bounce.
I also used SSV John Suhr pick up sets that I feel suitable to my taste.
I couldn't put the strap on the top wing like any other guitar as I find the top neck's too high & far from my body. My right hand couldn't reach the lower position fret. On the other hand, if I made the strap longer to make the guitar position lower, my left hand can't really position itself comfortably on the bottom neck. So I hung the strap on the headstock (like folk guitarist) to shift the weight centre in the middle of the guitar, hence the top nut became lower and I could reach the lower frets with my right hand.
"Jingle bells" was my 1st song on double guitar. It's also a practice for alternating bass playing utilizing the low B string. (I'm not a lefty, It's somehow the mirror effect of my iMac)
As I sling the guitar on the neck, another problem appeared...when I stood & sling the guitar, the top neck held the full weight of the guitar, hence the strings were pulled/stretched more & alter the tuning a bit. It means the guitar's tuning's different when I sat down & when I stood up.
I also found that the position of the guitar waist was to low, hence when I sat down & put the guitar on my lap, the neck position's too high.
So, I moved on with the next project with "better design".