The open tuning I used in "Big Sur" a tribute to Crosby Stills & Nash, is derived from the one used in "Suite Judy Blue Eyes" therefore : EE, EE (an octave over), BE (like on a normal guitar).
The fact that there's no third, gives this tuning a modal impression. Crosby & Stills favored these thirdless chords. Crosby in "Music is Love" is tuned DADDAD, Stills in "4+20" & in "Bluesman" with Manassas is tuned in both situations EbEbEbEbBbEb, 1/2 tone below Judy Blue Eyes.
All the strings resonating reminds us of sympathetic chords & drones, much like certain oriental instruments like the Central Asian Tar or the Northern Indian Sitar. An historical note reminds us that the word "Tar" that one finds in guitar, sitar, setar, dotar simply means "string".
The 60's were greatly influenced by the Indian culture and it's gurus. Through these tunings CSN found a way to emulate a sound made popular by the Beatles & Ravi Shankar without the hassle of learning a new instrument and a different musical system based on microtonalities. (The sitar much like the tar, the saz and a lot of eastern instruments, has movable frets that the musician adjusts according to the indian raggas or oriental maquams he needs to play).