I must add that after changing the strings on my guitarist's Gibson EDS-1275, having the headstocks closer together would prevent the use of a string winder which makes for a frustrating situation.....deep breath aaand go! I'd opt for a little bit of angle between the necks just for this purpose alone, kind of like Pete Townsend's aahem..modified Gibson.

I like the EDS-1275.  I considered buying one many times over the years, but I just couldn't justify its price.  The Epiphone G-1275 makes more sense.  It's based on Jimmy Page's doubleneck.  It actually plays and sounds better than the Gibson at less than 1/3 the price.  I think this is mainly due to the location of the tailpieces, much further back than on the Gibson resulting in greater string tension.  Also, the necks are Mahogany like Page's rather than Maple on the Gibson.
I like the necks to be parallel so I can reach the lower neck more easily.  I play my Basses at the same level standing as when I'm sitting.  To play the lower neck of a doubleneck with the necks angled apart would have the top neck right in my face.

While I, too, love Epiphones, I don't think you can lay any of their excellence relative to Gibsons (especially for the money) on the tailpiece placement.  Tension is the result of tightening the SPEAKING LENGTH of the string mass to a particular pitch.  The same mass string on the same scale length at the same pitch will have the same tension no matter how far you move the tailpiece (the same would hold true for tuning pegs).  
 
Peter

I disagree.  String tension is a function of string mass, scale length, headstock angle, tuning peg location, neck angle, how far the strings are anchored behind the bridge, bridge height and neck relief. Anyone can tell you that there's a significant difference between the string tension on a Jazz Bass with the strings anchored through the body compared to one with the strings anchored through the bridge, or a guitar with a regular inline headstock versus a reversed inline headstock.  You can increase the string tension without changing the scale length.
Perhaps I don't fully understand the definition of Speaking Length, but I know that string tension is constant throughout the length of the string from where it's anchored at both ends. The nut and bridge saddle do not hold the string securely.  It's free to slide over them.
The Speaking Length varies with each note played on the string without affecting tension. But then what do I know?  Maybe my fingers and ears are just telling me what I want to hear.
I'm sure that experts (such as those who build Alembics) can confirm or refute this.  I'm no expert.
 

 
As well, the Epiphone has Mahogany necks with a flame Maple top, the Gibson has Maple necks with no top wood.  I don't know what differences lie in their pickups or any other factor (other than tailpiece location) that may affect their sounds.  The Gibson costs $3500, the Epiphone cost around $900.  The Gibson is made in the U.S., the Epiphone is made in Korea.  
I'm not a particular fan or owner of either.
The Epiphone sounds better to me. It feels like it has greater string tension with greater sustain - in my opinion.
 
(Message edited by rami on March 28, 2008)

Kris. I work mainly in AutoCAD 2002.
 
I've tried the latest, 2008, because 2002 is VERY unstable in Windows Vista, but I don't like the way they've changed things in it.
 
Rami. For now it's mostly concepts, an exercise in what I can do in Autocad, get some ideas out of my head.
It would take very long for me to save the money needed, and I don't know how to play any instrument. I just have ideas.
 
Maybe time to learn...

I also passed up the opportunity to buy the John Judge when it was up for sale.  Something I'll always regret:
 

 
It was a money issue at the time.  The cost of a new one would be astronomical.  I hear it has a good home.  It'll probably outlive us all.

Damn. Those heads are closer than what I draw.
 
Scorpion body with omega and double points. Nice.

Yeah, the necks have to be close together to make it playable.  
Here's another Alembic beauty;
 

 
But I can't imagine playing this (for my style of playing) simply due to the difficulty reaching the lower neck.  The top neck would be almost across my face, my nose would be where the second cherub is located!
It's more art than instrument.
 
(Message edited by rami on March 29, 2008)

Heh.... an idea fueled by beeing awake to long...
 
Learn how to play both as a rightie and a leftie...
 
Both necks would then be the upper one...
 
(I definitly need more sleep)....

Steve Vai has/had a double-neck built that way - he'd play hammer-ons with both hands simunltaniously.  A gimmick - but a very impresive one.
 
Peter

Rami. If you get the neck dimensions from Mica, both for a 30 12-string and for a 30 6-string bariton,
I can do a design suggestion in AutoCAD. I won't be able to simulate the BtC, but a macassar ebony top should be possible.
Have to search the site for some good pictures. Purpleheart and normal Ebony have already been simulated (as seen in my renderings).

I also need the string gauges and -spacing.
 
(sorry for doublepost)

That's ok.  I was just oohing and aahing over that 12 string baritone. I wouldn't want to see the Doubleneck too well rendered.  It'll be too much of a tease!
 

Hmmmmm..... why do I get a really evil thought through my mind.... hehe.... maybe it'll be fun to tease.... temptation, temptation...

... more temptation.....