Erik,
what do you mean by loops?

A few decades ago I worked for Califone, which makes (or made) language labs, and I ran across a loop product which was a loop of wire that went around the perimeter of a room and acted like the primary of a transformer. Presumably there were several "turns" to this primary.

The headphones of this system acted as the secondaries, having just a coil that would pick up the varying magnetic field of the primary.

This was a real product! I have zero idea how they kept it from picking up 60Hz hum... is this what you're talking about?