The Appalachian mountain dulcimer is an American folk instrument and comes in all sizes and shapes: from a rectangular Tennessee music box to highly ornately curved violin-like shapes. People made them with whatever local materials that were readily available to them and traced the shapes that were pleasing to them. The oldest known dulcimers were found in Virginia, and were lozenge-shaped ovals. Later on, the hourglass shape emerged in North Carolina, West Virginia, and Kentucky. The shapes differed with some narrow shouldered, others rounder at the top, and varying degrees of curvature. For the most part, mountain dulcimers seemed to have settled on two main shapes: the teardrop/elliptical and the hourglass.
Unlike instruments such as the violin, where the measurements, angles and acceptable dimensions are highly standardized, a mountain dulcimer maker is free to bend and curve to whatever dimensions that pleases him. This allows for a high degree of creativity, experimentation and customization.
The two most important dimensions on a mountain dulcimer are the fretboard scale length (also known as the VSL: Vibrating String Length), and the overall volume in cubic inches. The VSL roughly determines the overall length of the fretboard, which then in turn determines the overall length of the body. The afterlength (distance from bridge to string pins) is determined by making sure there is at least a 15 degree break angle over the bridge. Most dulcimers with a 25-26" VSL end up with bodies around 28" long.
The overall cubic volume of the dulcimer is determined by length, width and height of the body. In general, a larger body volume would give a deeper boomier sound. Whereas a smaller volume gives a more crisp, focused sound. The height of the sides vary from 1-1/2" to over 2-3". Older traditional dulcimers tended to have 1-1/2" sides, with short afterlength, the bridge right up at the end of the fretboard, giving them a brighter plaintive tone. These dulcimers were made before the introduction of the guitar to America around the turn of the 19th to 20th century. Contemporary dulcimers, those made after the Folk Revival of the 1960's-70's, tend to have taller sides, 2" or more, and a longer afterlength, allowing a more sustained mellower more guitar-like sound. Of course, these are broad sweeping generalizations, and there are more and many factors that are believed to affect the sound: wood choices, body shape, soundhole size/shape, bracing material, string gauge, and even pick choice.
Dulcimer tops, backs and sides are made of thin slabs of wood, 1/10" to 1/8" thick. The usual width of the top and back is between 6-1/2" to 8" at the widest.
Most older dulcimers have a scroll similar to a violin or cello. The pegbox is closed like a violin, with wooden carved pegs that are tapered. The pegs fit into the pegbox with holes reamed to the same taper. The ordering of the strings on the pegs is exactly the same as on a violin, in terms of position. The outer two strings in the lower peg on each side respectively, and the middle two strings on the higher peg.
After the Folk Revival, some dulcimer makers began using the guitar style peghead to attach the dulcimer strings. People who are used to stringing the guitar found it easier to work with than the traditional wooden tuning pegs. Modern makers of scrolls now use mechanical tuners in place of the wooden pegs for ease and convenience to the modern player.
The exact design of the scroll/peghead is as individual as the maker. The only guidance is to allow for a 15 degree angle down from the nut to the pegs. This gives sufficient downward pressure to keep the strings tautly in place.