Magnetic Field Transmission
This does work. I heard back in the 70s that a museum in the US had loops in various rooms and issued a special headset to each visitor - each room they entered gave a different commentary. I suspect that they may have used modulation techniques BUT I know it works because back then I tried it. I could just about hear stuff in headphones and I built a small amp (single transistor) and it was cool.

I powered it from an audio amp with a 6 ohm current limit resistor to prevent short circuits and it seemed fine.

TL082 - there is something you can use on this site - I've seen a circuit for a tunnel transmitter that relied on capacitive connections to the receiver. It could also transmit. If I can find it i'll post a link. It used a TL082 but virtually any op-amp configured for a gain of about ten to 100 would do the job.

Link - here

The headset - due to the cable or some other coupling impedance in the headset both earpieces could become "lightly" connected and thus one acts as receiving loop and couples energy to the other.