Many newer Hammered Dulcimers have a D# as the top bass bridge note. Why you would want one is another topic, but having it opens up the possibility of a nice B or B7 chord to add colour to your arrangements, for instance.
With smaller dulcimers (12/12’s and 15/14’s) this can be at the expense of the C, in larger dulcimers 16/15’s and above this is normally above the C. Some may have even higher notes on the bass bridge, I am sure as I am writing this some maker somewhere is adding more strings and notes!
So, can I just tune my old C to and D#? Well, that depends on your nerve and if you fancy having a go at changing strings! But seriously the top strings are pretty near breaking strain and moving to thinner strings just means it doesn’t make you jump as much as when the thicker ones snap. The maths suggests using thinner strings doesn’t reduce the breaking strain. It will, of course, change the tension, and in practice will reduce the strings desire to pull through the eye of the tuning pin, but lets just look at breaking strain. Using a thinner string may give you a little more latitude but not much.
Just to be clear, the length of the string I will refer to is the “sounding length” so is the part of the string you strike that goes from the top of the bass bridge to the side bridge.
For my instrument the maths said my top C string at 38cm long is at about 47% breaking strain, tune that to D# and it goes to 67%,. A whopping 20% increase and somewhere, I would suggest, you don’t want to go. Out of interest a gauge 6 string goes from 16kg tension to over 22kg, again, not somewhere we really want to go.
Hammered Dulcimer string design is all around the Goldilocks principle, the bottom strings are too short, the top strings are too long but the middle strings are about right. So we have to go for a compromise. Ideally the shape of the dulcimer would be the same as the harp or piano, but then it wouldn’t be a dulcimer. So we end up with the top strings being longer than we would really like and nearer their breaking strain that we would like.
The solution, or certainly a solution, is to fit a small bridge, or “bridgelet”. I experimented with one and if I left my top C string tuned to C and fitted a small extra side bridge about 5cm from the original side bridge I can get a D#. So not much extra tension on the string and no change in breaking strain. Looking good.
However I found it a bit hollow and banjo style, which is due to the string not “breaking” on the new bridge, so some of the energy was going to “the other side” of the bridge and sounding. So I pushed the bridgelet a little closer to the original side bridge, to about 3 1/2 cm, here is sounded a D. I did the maths and to tune a 34cm string to D# took it to 53% breaking strain. So, I was happy with that.
I would add my usual “Caveat Actor”, let the doer beware! Always wear eye protection when experimenting with strings. I needed them just once, luckily I was wearing them and it made me jump but no hospital visit required.
I made the bridge around 15mm long which worked well my 12mm long Delrin bridge tops.