5 string dulcimer
General mountain dulcimer or music discussions
I have a Bill Berg 5-string hourglass that measures 27-1/2" from nut to bridge. Bill recommended these string sizes:
.24-.09-.13-.11-.11
The wound bass string is on the outside. For the inner string on the bass course I often use a .10 instead of a .09 and it works fine. You can try .11 if you want, but I don't think string size is your problem. Bill knows how to set up a dulcimer and I am certain your MD did not leave his workshop with string interference.
Ken's right that changing strings is the first thing to try, since it's easy. But I'm wondering: does your MD have the original nut and bridge? Have they been damaged? If somebody took a file to the bass slots (perhaps to install a second wound string instead of a thin octave string) then they could have messed up the string spacing. The .09 string should fit snugly in its slot. If you can, post a close-up photo of the nut and bridge.
Rarely do I pass up an opportunity to suggest that people learn how to strum with a lighter touch, but unless you're strumming like a gorilla that isn't your problem; it's the dulcimer's problem. :-)