Scale length
General mountain dulcimer or music discussions
Adding to what Dusty said, tone can also be greatly effected by the wood thickness... not simply by the size of the sound box and its scale length.
And also, having the correct amount of tension to complement the thickness of the box. Thicker wood can need more string energy to get excited, so an instrument intended for high tension can sound more hollow with low tension. Kind of like when you put nylon strings on a steel string instrument.
