The harmonic frequencies are integer multiples (2, 3, 4, …) of the fundamental frequency. For example, the 2nd harmonic on a 60 Hz system is 2 x 60 or 120 Hz. At 50Hz, the second harmonic is 2 x 50 or 100Hz. 300Hz is the 5th harmonic in a 60 Hz system, or the 6th harmonic in a 50 Hz system. What this all means and has to do with faithful reproduction … watch this episode of Tech Talk to find out !