How is the 3rd harmonic defined in relation to the 2nd harmonic?

The 3rd harmonic is defined as occurring a fourth above the 2nd harmonic because of the way harmonics are structured in a simple musical context. In a harmonic series, each harmonic is an integer multiple of the fundamental frequency (1st harmonic).

When you analyze the harmonics, the 1st harmonic is the fundamental tone itself, the 2nd harmonic is the first overtone and is effectively an octave above the 1st harmonic. Thus, the 2nd harmonic is at twice the frequency of the 1st harmonic. The 3rd harmonic, being the next step in the harmonic series, is at three times the frequency of the 1st. The frequency difference between the 2nd and 3rd harmonics can be calculated as follows:

• 2nd harmonic: 2 times the fundamental frequency.

• 3rd harmonic: 3 times the fundamental frequency.

To find the interval between the 2nd and 3rd harmonic, note that the ratio of their frequencies is 3/2, which corresponds to a perfect fourth in musical terms. Therefore, the 3rd harmonic is indeed situated a fourth above the 2nd harmonic, making this choice the accurate definition within the