Susan of DT's comments are very good. I've been playing hammered dulcimer for three years and am absolutely enthralled with it. My instrument is a 12/11 with 52 strings in 23 courses over two bridges. That seems to be the most common size, but there are both smaller and larger ones, with one or more bridges. Some folks even play fully chromatic ones. The 12/11, however, in standard tuning, lets you play probably 95% of the trad and folk out there. More tunes than I could ever hope to remember anyway.