Harp string tuning can vary depending upon the player and/or the notes needed for a particular song. This string gauge calculator is helpful for finding the correct string gauge for the note/frequency you wish to achieve for the scale length of the string. The rule of thumb is to try and get approximately 22lbs per string for light gauge steel core – phosphor bronze wound strings.
The commonly used tuning for Larson and Knutsen instruments is diatonic, which starts the first harp string at a whole step lower than the low E on the guitar, or D, then tune each subsequent string a scale note lower than the previous string, so D2,C2,B1,A1,G1,F1 (descending).
Stephen Bennett developed a tuning for his harp guitar that starts the first harp string at a G2, then the next at D2 and descends down from there to G1, so G2,D2,C2,B1,A1,G1. Of course the performer/composer can choose whatever tuning he/she wants for the harp strings, usually to accommodate the key of whatever piece of music is being arranged/played. Re-entrant strings are those which are positioned lower than the one above it but are a higher note. They can be useful in achieving different finger picking patterns as in the tune “Because Its There” by Michael Hedges. Just make sure to use the correct gauge of string for the length so you don’t put too much tension on the instrument.
Strings sets can be purchased for the S-12 diatonic tuning at the harpguitarmusic.com website
***Disclaimer*** Please use caution if you choose to experiment with other tunings! Tuning a string up with too high of tension can damage your instrument, please calculate which gauge of string is best for the note you wish to achieve, keeping in mind you want no more than 24 lbs. of tension per string, light gauge is approximately 20 lbs.