The zapper effect is frequency independent. The zapper is frequency independent because its mechanism is the positive offset. This way it will generate a current flow through the body, something the mixed offset will not do.. The square wave has many harmonic frequencies and will hit many frequencies. If you use 30kHz, then you will have harmonics at 90kHz, 150kHz, 210kHz (odd multiples) and so forth. Because no zapper generates an exact square wave, you will actually have harmonics on 60kHz, 120kHz, 180kHz (even multiples) also.
The frequency generator produces specific frequencies.
