Did you read the information, Install Telecoil or Not in your hearing aids?
To add to the above post:
The “loop” (whether a neck loop, room loop, table loop) uses magnetic induction technology. (Remember your high school science class winding wire around a magnet?) It sends the sound from the loop to your hearing aid. To get the sound from the sound source to the loop, I use an audio cord (so it is not bluetooth for me) from the sound source (head phone jack) to the head phone jack in the neck loop. Auditoriums can send the sound from their sound board to that black receiver box, which ushers hand out (and which connects to your neck loop) via FM Radio waves. (or there is Infared Technology --instead of FM Radio-- for some auditoriums). That is all the technology I know.