There is no real consensus on the “ideal” sound and response for a hammered dulcimer, and instruments by different makers vary quite a bit. In general, tones range from a chiming bell-like quality through a deeply resonant piano-like sound.
Sustain, or the length of time a string continues to ring after it is struck, is an important consideration for most players. Too much sustain will quickly muddle a tune, while too little will sound stark and thumpy. Without dampers, dulcimers have no way for the player to adjust sustain or “damp” the strings, but the instrument’s bracing and construction can be designed to control the amount of sustain.