How come there are so many different string spacings and number of strings on mountain dulcimers?
The 3-string arrangement is probably where it all began, and still where a large percentage of instruction is focused. 5-string dulcimers are usually arranged in three courses: a double melody, a single middle string, and a double bass string (which can be a unison or octave course). Six-string dulcimers are simply 3-course dulcimers with double courses, and the bass course may be a unison or octave pair. An 8-string dulcimer, likewise, is simply a doubling of the 4-string equidistant set-up; again with the optional octave on the bass course.