Yes, I am aware of Janita Baker's DAA#d tuning. What I was trying to achieve with the DADb tuning is to allow my fretting hand to add more complex chordal arrangements and harmonic flourishes to music that is tabulated DAD while also allowing me to strum (and not just pinch the DAD notes, as Baker's tuning would require).
4-string dulcimer DADB tuning (5th and a 3rd)
You might want to check the list of Groups here and see if there are some groups aligned with your interest. There are groups for 4 strings, baritone dulcimers, classical music, and many more that you may find of interest.
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updated by @ken-hulme: 04/25/19 07:08:34AM
Hello, All! After a very long absence, I have returned! I am a classically trained pianist and am very drawn to the harmonic (or even inharmonic) complexity of classical music. That's not to say I'm not interested in various kinds of music—I am. But I am excited most by novel harmonies and chordal structures. Because of this, I purchased two McSpaddens, one with the 1+ and 8+ frets and one chromatic. (My McSpaddens also allow me to convert them from the standard string arrangement to a baritone string arrangement without much trouble.) I've also bought a lot of tabulature (for three strings) but have found much of it too simple in its harmonic structures (and very simple to play, too). I played around with various tunings on my semi-diatonic dulcimer using only three strings but have found that still somewhat limited. I thus have focused more on trying to use a 4-string arrangement (with a DADB tuning, employing a 5th and a 3rd). Anyone tried using a four-string arrangement, playing more complex harmonies? I'll be grateful for any feedback!! Thanks!