For instruments with between 19 and 40 strings, tuning a Celtic harp can be a daunting prospect. Whether it is a steel strung Scottish clarsach or a nylon strung Irish harp, the tension in the strings is so large that the harp permanently can be damaged if tuned incorrectly. However, by applying a few principles, the harp safely can be tuned to the correct pitch without professional assistance. Tuning a harp can take up to a week, but once it has settled, it holds its pitch and tone for a long time.
Find the correct pitch the lowest string. This information is found in the documentation that came with the harp or by asking the seller. If the harp is nylon strung, the strings may be colour coded. The C string is red, and an F string is black. Contact a music store for a harp string calculation sheet if unable to determine the lowest string. Measure the length of the string, and compare it to the calculation sheet. The lowest note on a Celtic harp usually is a C or a G.
Construct a string guide. Take the piece of paper, and place it beside the strings where they meet the soundboard. Cut a little slot for each string so the paper can fit over the strings. Take the paper off the harp, and write out the pitch for each string. Celtic harps are tuned to the key of C. Start with the lowest note, for example C. From lowest to highest, this is C, D, E, F, G, A, B, C, D. Continue up the scale until you reach the last string.
Determine how much the harp is out of tune. Place the string guide beside the harp so you can see what the pitch of each string should be. Pluck each string, and use the electronic tuner to find its current pitch. Write down the pitch.
Decide the tuning stage in which you should begin. The harp takes four days to bring it up to the correct pitch when newly strung. On the first day, tune the strings three semitones below the intended note. The strings C, D, E, F, G, A, B should tune to A, B, C sharp, D, E, F sharp, G sharp at stage one; B flat, C, D, E flat, F, G, A at stage two; B, C sharp, D sharp, E, F sharp, G sharp, B flat at stage three; and C, D, E, F, G, A, B at stage four. Start on the stage where you have at least one string flatter than the target pitch.
De-tune any strings that are sharper than the final target pitch. If a number of strings are sharper than intended, start on the shortest string and work toward the longest. Fit the tuning key onto the string's tuning peg. Pluck the string, and slowly turn the key to flatten the note to its target pitch. Turn counterclockwise in most cases to flatten a string; however, this is reversed on some harps.
Tune the flat strings to the target pitch of the selected tuning stage. To keep equal tension across the harp, tune all C strings first, then all G, D, A, E, B then F strings. Do not tune any strings that are sharper than the target pitch for this stage. Let the harp's wood to settle for 24 hours.
Tune the harp to the target pitches of the next stage as outlined in Step 6. Let the harp sit for 24 hours, then repeat until the final target pitches are reached. Some fine tuning may be required during the next couple of days.
Take plenty of time to tune the harp. There is increadible tension even in the smallest harp, and overworking the strings can damage the harp. Tune the strings slowly. The strings can break if the keys are turned too quickly.