When I first began playing hammered dulcimer around 1975 the most common instruments had 12 courses over the treble or center bridge and 11 courses over the bass or left bridge. Hammered dulcimers are often described by the number of courses over the various bridges. The dulcimer described previously would be referred to as a 12/11.
I first learned on a 12/11 and it proved to be a versatile and intuitive instrument. The lowest note was G below middle C and it played easily in D, G, C, F, A and all the modes and relative minor keys based on those scales. The various scales offered enough notes that could be borrowed to get most of the accidentals I needed and in a pinch I could retune one or two courses to give me a note outside the usual pattern.
I played a number of 12/11 dulcimers through the mid 1980’s. During this time most other professional players were playing dulcimers that were 15/14, 17/16 and the various chromatic dulcimers that often had a few extra bridges.
I began to follow the trend and played a wonderful Cloud Nine 15/14 for a few years. Then Michael Allen of Cloud Nine made me a fully chromatic dulcimer that went down to G an octave below middle C. I loved the extra bass notes and these instruments inspired new directions in my playing.
Over the years I have developed some back problems that are aggravated by playing the hammered dulcimer. In my search for ways to overcome this I occasionally would play a smaller dulcimer, usually a 13/12.
The lack of lower range caused me to be more creative with harmony and chord voicing. There is an intimacy I feel with the instrument that escaped me when playing a large dulcimer; there is less distance, in a manner of speaking, between myself and the instrument.
I also appreciate having less strings to keep in tune and less weight to haul around.