A fiddler can play any key using only stopped strings; the comma doesn't enter into it, nor the 'tempering'. Many folk styles (if not most) use open strings where available both for melody notes and/or drones. That's when B becomes problematical.

Okay, I can see that B might become problematical if open strings are being played. But I don't think bluegrass fiddle players use open strings when playing in B, that's why they don't have to hurt their heads while playing.

For some reason, I've been under the impression that classical violinists also eschew playing open strings. The open string has a slightly different tonality than a stopped string and they strive to effect the same tonality through an entire passage. Do I have this wrong?

      - Mark