Pole placement matters, but it's not really crucial that it be exact.
I like your idea of using a 6-pole guitar pickup for a 3-string bass... You can always angle the pickup to match the string spacing!
Easier still is to use a pickup that doesn't have pole pieces but picks up evenly along it's surface, lots of soap bar pickups are like this, as are blade style pickups, like this one.
I like the dual rail pickup you referenced. Know of any pointers to how it gets wired up with the 4 leads? I'd probably want a volume knob (but I don't imagine I'd add a tone knob).
Well you can hook the coils in parallel, but I generally just tie two of the wires together, and use them in series. I forget the color code offhand, but it comes with a sheet, and theres diagrams online. I find this site informative.
hope that helps.
the poles are to conduct the magnetic field from the magnets inside the coil up to the strings.
you "might" notice a difference if on string is between poles and the other is directly over a pole, but then again you might not.
you could adjust your string spacing to match the poles on the pickup, angle the pickup to match your string spacing, do both, and/or put a bit of flat iron across all the poles to even out the field.
Thanks for the info, JL. I ended up ordering one of the dual bar type humbucker pickups.
Wow, the more I get into this project, the more it multiplies...
At this point I think I'm going to make two different bass instruments:
1) A two or three string cigar box bass using string trimmer line, and
2) An upright "stickbass" (inspired by Steve Joy's JoyStick Bass instruments) using flatwound bass guitar strings. This one will probably be stand-mounted like I've seen for Electric Upright Basses (EUBs).
So, for #1... I understand string trimmer line needs a long period of stretching out before it's stable. I'm prepared for that. What I'm wondering is... Given that string trimmer is not so easy to tie a knot into, what have others done about the tailpiece end to hold it into whatever hole it is threaded through?