Here is a gross generalization, but it helps in understanding the function of scale lengths:

smaller/shorter instruments are often tuned to higher pitches and octaves and have thinner strings. (think violins and mandolins)

larger/longer instruments are often tuned lower pitches and have thicker strings. (think 'cellos and double-basses)

There are many combinations of string gauges, tunings, and VSLs that will 'function' for various goals, but keep in mind that as you stray further and further from the ideal gauge for a given length and note, the more unsatisfactory the result will be. Extreme examples of this concept are: 1) putting thin violin strings on a cello and trying to tune it to the same violin high notes, and 2) putting thick cello strings on a violin and trying to tune it to the same low cello notes.  Hope this helps.

Thanks Dusty

For reference purposes: Blue Lion's bass dulcimer has a 27.5" scale length and they use .052w for the bass, .032w for the middle, and .024w for the melody.

More and more luthiers are making dulcimers with shorter scale lengths, even for baritone and bass dulcimers.  New Harmony is now making baritone and bass models with 25" and 26" scale lengths. You might contact Rick there and see what they use for string gauges.  To really get a bass sound I think you need pretty heavy strings.  Those recommendations Ken got from the String Calculator--always the place to start--are pretty close to what I use on my 27" Probst strung as a baritone. (34, 24, 16).

Hi Ken, 

  I caught the Prime mark on the string Calculator, TY for the info

Sorry Bill, I mis-wrote that tuning below...   A Bass Dulcimer 1-3-5 tuning is designated D'A'D or C'G'C. 

Notice the ' marks on the first D and A.   This tells us that those notes are a full octave lower than the common DAd. 

In fact, on a bass dulcimer the melody string D is the same as the bass string D on a regular dulcimer.   If you look on the Strothers Calculator that I posted below, you will find that for your very short VSL Bass Dulcimer you will need the following strings:

D' = .035
A' = .027
D = .020

You won't be able to put those strings on a regular dulcimer nut and bridge -- the slots will be too narrow.  If you're trying to make a bass dulcimer out of a regular dulcimer, you will need to open up the string slots on the nut and bridge, with a small triangular file, so the strings can sit properly. Not particularly deeper, but wider.

Most bass dulcimers that I have seen over the years have had much longer VSLs -- 28", 29" even 30".  

26.5 VSL

As always Bill, we can't help with string gauges unless you also tell us what the VSL of your dulcimer is.  Once you have that and the base tuning you want -- DAd (not DAD)  -- you can use the Strothers String Choice Calculator and plug in the numbers yourself:

Tom & Missy Strothers | String Choice

What  gage  strings are used for a bass dulcimer tuned DAD?