Does a dulcimer get a fuller tone when broken in?
General mountain dulcimer or music discussions
In my experience, which is somewhat limited, a dulcimer's 'voice' DOES seem to change. I'm speaking from a new build standpoint, but I think it would apply to a newly purchased, new manufacture dulcimer as well. It may not always be fuller, but I do seem to detect a change in almost every one I build. Some do sound fuller. There is also the factor of your ear developing a tolerance for the new sound.
All that being said, I think several factors change the sound of our dulcimers. New strings, different gauge strings, a different key or even something as subtle as a change in humidity could make a difference.
I also seem to notice a difference when I play with fingers or a noter.
A good question and I'm sure there will be some fascinating discussion on it.