Induction loop systems consist of a thin wire that is placed around the listening area*, a special amplifier and microphone(s). Speech signals are amplified and circulated through the loop wire. The resulting magnetic energy field is detected and amplified by the "telecoil" or telephone switch circuitry common to more than 50% of hearing ids now being sold and growing, cochlear implants and induction loop receivers. The end result is a high quality amplified reproduction of the original speech signal. Intelligibility is greatly increased because the distance between the speaker and the listener(s) is bridged and background environmental noise is reduced.  

To read more go here: http://www.hearingloop.org/fq_broadcasts.htm