Yup, on the order of below 100 Hz usually https://en.wikipedia.org/wiki/Extremely_low_frequency .
Below a certain point do you suppose my headphone jack can double as a transmitter?
Technically, yes. Also a lot of people in the amateur radio community use the microphone in as a receiver for VLF transmissions.
Below a certain point do you suppose my headphone jack can double as a transmitter?
Technically, yes. Also a lot of people in the amateur radio community use the microphone in as a receiver for VLF transmissions.