DAA or DAD as primary tuning ?
General mountain dulcimer or music discussions
Don, a while back I wrote a short explanatory piece called " What are extra frets and do I need any? " You might check it out.
The simple answer to why you would use an extra fret is to get the note produced there. For example, there is no F natural on a diatonic dulcimer tuned DAA or DAd. So if a song has that note, you have to skip it, bend a string, or use an extra fret. If the song is modal you can retune to get an F natural, but not all music is modal, and as Lois says, "accidentals happen." An "accidental" is simply a note that is not in the scale. But not all songs are limited to the 7 notes of a diatonic scale. I am learning a French Canadian tune right now called "La Galope de la Balbaie" that necessitates the use of the 1-1/2 and 6-1/2 frets on the middle (A) string.
The original reason, supposedly, for the 6-1/2 fret was to be able to play songs in the ionian mode out of a mixolydian tuning. Those are the two most common modes, so the extra fret obviated the need to retune. And the 1-1/2 fret offers other possibilities. As Jan suggests, it makes playing a C chord easy to do down by the nut since the 1-1/2 fret on the middle string gives you a C natural (also found on fret 6 of a D string). When I play the B part of Old Joe Clark I play a C chord, which all guitarists and mandolin players do as well, whereas dulcimer players are unable to do that and play a much less dramatic A chord. That C chord also shows up in other traditional fiddle tunes such as Red-Haired Boy and Salt Creek. And as Jan explains, having an easy C chord near the nut allows you to play chords in the key of G very easily.
I also use the 1-1/2 fret to play the blues. The most important "blue note" is the lowered third, which is an F natural in the key of D. But importantly, that note gains its power from the fact that it is played over the major chord, so you still need an F# to play the blues. In other words, re-tuning won't help. But the 1-1/2 fret gives you the lowered third (F) on the melody string and the lowered 7th (C) on the middle string. And since most pop, blues, and jazz melodies us the minor pentatonic scale, that comes easily with a 1-1/2 fret. Starting on the bass string play 0, 1-1/2, 3 then on the middle 0, 1-1/2, 3, and you have your minor pentatonic scale to play over the major chords of a pop, blues, or jazz song.
My sense is that if you have to ask why anyone would want extra frets, you probably don't need them. The 6-1/2 is pretty standard these days, so if you play with a dulcimer group, it will likely be expected that you have one. Unless you specifically want to play non-diatonic music for which the dulcimer was never intended, you do not need a 1-1/2 fret. Having said that, I love mine and won't give it up!
updated by @dusty: 08/06/17 09:23:37PM