The short answer
A vaulted fretboard is arched so it does not sit flat against the soundboard. The air gap lets the top vibrate more freely, which produces noticeably more projection and a fuller tone than a flat-fretboard dulcimer of the same size and wood.
A 6½ fret is an extra fret added between the 6th and 7th. On a dulcimer tuned DAD it gives you the note that lets you play in the Ionian mode, which is ordinary major-key music, without retuning. Without it you are limited to Mixolydian from DAD tuning, which rules out a large share of common songs.
If you are buying one dulcimer and want it to handle the widest range of music, buy one with both.
Why the fretboard sits above the soundboard
On most fretted instruments, the fretboard is on the neck and the neck is separate from the body. A mountain dulcimer is different. The fretboard runs the whole length of the instrument and sits directly on top of the soundboard.
That creates a problem. The soundboard is the part that makes the sound. Anything pressed against it damps its motion. A flat fretboard bonded along the full length of the top is a long stiff bar sitting on the exact surface you want to move freely.
A vaulted fretboard is arched, hollowed underneath, so it contacts the soundboard only at intervals. The top is left free to vibrate across most of its area. The difference is audible: more volume for the same effort, longer sustain, and a fuller low end.
Flat fretboards are not a defect. They are simpler to build and they hold tuning well. But when two dulcimers are otherwise similar and one is vaulted, the vaulted one will be the louder and rounder instrument. Every dulcimer in our mountain dulcimer collection uses a vaulted fretboard.
The 6½ fret, explained without theory
Mountain dulcimers are diatonic. Where a guitar has a fret for every half step, a traditional dulcimer has frets only for the notes of one scale. That is what makes the instrument so approachable: almost anything you play sounds right, because the wrong notes are simply not there.
It is also the limitation. In standard DAD tuning, the traditional fret layout gives you the Mixolydian mode. Mixolydian is the major scale with a flatted seventh. It is beautiful, it is all over old-time and modal Appalachian music, and it is wrong for a huge number of songs people actually want to play. Try "Amazing Grace" or most hymns and popular melodies from DAD on a dulcimer with no 6½ fret and you will hit a note that sits a half step below where your ear expects it.
The 6½ fret supplies that missing note. With it, DAD tuning gives you the Ionian mode, which is the plain major scale, and the Mixolydian is still available by using the 6 fret instead. You gain the second option without losing the first.
Many dulcimers with a 6½ also carry a 13½, which is the same note an octave up, so the option holds when you play higher on the fretboard.
Do you need it?
- Playing traditional modal tunes and old-time repertoire: you can live without it. Plenty of players do, deliberately.
- Playing hymns, folk songs, popular melodies, or anything from a general songbook: you want it. This is the majority of what beginners bring to the instrument.
- Playing with other people: you want it. Retuning between tunes to reach a key you could have fretted is slow, and it puts you out of step with the group.
The Grace Mountain Dulcimer carries 18 frets including the 6½ and 13½, on a 25.5 inch scale. It is also built in walnut, which gives a slightly brighter and drier voice than rosewood.
Three strings or four
The other question that stalls dulcimer purchases, and it has a simple answer.
A traditional dulcimer has three strings: one melody, one middle, one bass drone. A four-string dulcimer doubles the melody string into a pair tuned in unison. You still fret them as one string. Your left hand does exactly the same work.
What changes is volume and texture. The doubled melody string is louder and has a shimmer to it, similar to a 12-string guitar, which helps the melody carry over the drones and in a group. The tradeoff is one more string to tune and slightly more finger pressure to press two courses cleanly.
Four strings is the common modern choice and what we would suggest to most beginners. Three is lighter, simpler, and truer to the older sound. A three-string trail dulcimer is also the practical choice if you want something to take camping.
Five-string dulcimers double both the melody and the middle string. The five-string Grace is a fuller sound for players who already know they want it, not a first instrument.
Scale length, briefly
Scale length is the vibrating distance from nut to bridge. It sets fret spacing. A 25.5 inch scale is standard for a full-size dulcimer and is what most instructional material and tablature assumes. Shorter scales pack the frets closer together, which suits smaller hands and children, and gives a slightly tighter tone.
Unless you have a specific reason, standard scale is the right choice. Body shape is a separate matter: hourglass, teardrop, and the round-hole specialty shapes all sound slightly different and none of them is better.
What to expect when it arrives
Your dulcimer arrives strung and set up, and it arrives out of tune. Strings shift under changing temperature and humidity in transit on every fretted instrument that exists. Tune it to DAD before you play, and expect to retune for the first week or two while new strings finish stretching.
DAD means the bass string is D, the middle is A, and the melody strings are D. Your open strings already spell a D chord, so strumming across all of them produces music before you have fretted anything. Most people find a simple melody within the first fifteen minutes.
Where to go from here
If you want a vaulted fretboard with the 6½ and 13½ frets in the standard configuration, that is the core dulcimer collection. If you are weighing the dulcimer against other folk instruments, our guide to choosing a first folk instrument covers the honest tradeoffs. A capo is the cheapest way to add keys once you are playing, and every dulcimer includes an owner's guide covering tuning, restringing, and care.