Hi Paula, the first Dulcimer I had made back in the mid 70's had a cedar top, since then I've made 4 with cedar tops and a few with spruce. My personal choice is cedar I love it's lightness and mellow sound.
Hey Paula. Traditionally, dulcimers were usually made entirely of local hardwoods and there was no difference between the sides, bottom, and the top. A lot of people still prefer dulcimers made entirely of walnut or other woods. But more modern makers began using soft tone woods such as spruce, cedar, and redwood on the top to produce a softer, more guitar-like sound.
Most guitars have a spruce top. Spruce is a little harder than cedar and resists scratches and nicks a little better. But cedar produces a similar sound and usually much quicker. What I mean by that is that it sometimes takes a while for spruce to fully open up, which is a main reason guitars getter better with age. Cedar usually gets that sound much earlier in an instrument's life.
I have dulcimers with spruce, redwood, and cedar tops and they are all great. The sound differences between them are due more to other aspects of instrument design. Don't shy away from a cedar top if the rest of the dulcimer has what you're looking for. It's a highly respected tonewood.
Dusty T., Northern California
As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie
updated by @dusty: 10/26/21 05:46:03PM
Depends on to whom you are talking. I have heard some describe it as a sweet sound and others a bit trebly. Cedar is lighter wood than spruce or almost any hardwood (balsa is a hardwood.) The instrument should be lighter. It is also a little weaker than other woods, so might get damaged more easily.