[rini17]

Induction loop disadvantages:

* Poor frequency response

* Only one channel

* They pick up mains 50/60Hz hum and other disturbances from power electronics

* works best when whole room is inside the wire loop, which isn't always possible. Portable "wireless" systems exist but have range at most few meters.

Advantages:

* technically very simple, reliable, not encumbered by patents

* most hearing aids have the receiver coil

...and this is why hearing aid manufacturers hate it. They prefer to sell proprietary devices. There were attempts to move to FM radio but as everyone does it differently and both transmitters and receivers are expensive, it isn't widely used. Newest hearing aids come with bluetooth, I've no idea whether it can be reliably used this way (simultaneous streaming to multiple bluetooth devices).