broadcast audio signal

That's a huge bandwidth, about nine octaves. You can do it over short ranges with magnetic coupling, but if you want more than a few feet of range, upconverting to RF or modulated light is the only way to go.

...... Phil

Yes, It's done for hearing aids, it's called an inductive loop and has only a short range.

Bye. Jasen

Induction loop. That'll cover a modest area.

Graham

If you actually want this to be an RF signal (in the Extremely Low Frequency range) you will need the mother of all antennas. IIRC, the US military (used to?) use this range for communications with submerged submarines. For a while they planned to use the entire Upper Penninsula of Michigan as the transmitting antenna, by virtue of its extensive iron and copper deposits. The system was intended for transmitting (at incredibly low bit rate) simple nuclear missile launch instructions. There was a big flap over it at the time (1980s maybe?), then we never heard any more about it. Hopefully it died with the cold war. But then again, one might have said that about the Star Wars projects as well, and they seem to still be with us....

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Worldwide system

Michigan ELF

"Submarine Communications Master Plan (December 1995)"

It is easier to find out US nuclear secrets, than what Karl Rove is up to.

They use induction loop systems for the hearing impaired in auditoriums - big loop in the floor is modulated with the audio signal and individual receivers pick up and amplify the signal. Better than a hearing aid, because you don't amplify the ambient noise just the program material.

Some folks used to put them in their houses for music and there might be some info on the web how to go about it on a small scale.

How about a loudspeaker?