A bell is unlike any other instrument because it actually produces multiple notes, called partials. Tuning a bell is a time-consuming process that requires the bellfounder to be proficient with both a simple tuning fork and high-end digital tuning equipment.
Using a lathe, metal is shaved from inside the bell at various points until the proper tuning is achieved. The bellfounder must tune the five lowest partials, at a minimum, to the standard of A3=440 vibrations per second.
From the lowest partial to the highest, the notes are:
- The hum (an octave below the prime or “strike” note)
- The prime (an octave above the Hum)
- The minor third (of the Prime)
- The fifth (of the Prime)
- The octave (of the Prime)
While the prime tone is the most important note of the bell, the hum tone, the minor third and the octave must be tuned with the same accuracy. Of particular interest is the minor third, which is unusual in a musical instrument.
Although the profile and tuning process works to intensify the prime while subduing the minor third, it is the minor third that gives bells their beautiful, melancholy, plaintive and compelling sounds.