Old dulcimer tuning dissatisfaction
I've explained this before and got blank stares so...
Get bridge properly set for octave at 7th fret.
In DAA for example. If your melody string doesn't ring sweetly with the drones, like unisons fifths and octaves, you may not have a DAA compatible dulcimer.
Don't give up on it. I have one. Frets have been set by ear or some given table not equal temperament.
Try different tunings. I compensate by tuning DGd or DGC b/c they do ring true with unison octaves fifths on my dulcimer.
If you have an old dulcimer not being played b/c of tuning dissatisfaction try a different tuning. It might ring like a bell.