A more detailed downloadable comparison document is attached below.
Assistive Listening Systems - These systems transmit amplified sound to the user via hearing aids, headsets or other devices. They include Audio Frequency Induction Loop systems (aka Hearing Loops), FM systems and infrared systems
Assistive Listening Devices (ALD's) - ALDs are the technical devices that form the assistive listening system that improve communication in difficult listening environments. They are used to minimize the effects of noise, echoes, and distortion encountered when a hard of hearing person listens to speakers at a distance or in a noisy place. Examples: Audio Frequency Induction Loop, FM or Infrared systems.
Audio Frequency Induction Loop (AFILS) Systems - Audio (frequency induction) loop systems consist of a wire (or thin loop pad) 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 many hearing aids, 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. The loop is available in three formats 1) A hard-wired system built into the walls of a meeting room 2) A portable system that can be moved from room to room as required and 3) A smaller fixed or portable version used at customer service counters. Immediately useful wherever it's installed by simply setting your own hearing aid to the 't-coil' position.
Frequency Modulation (FM) Systems- FMs are assistive listening devices (ALD) that functions as a mini-radio station on a broadcast frequency that brings a speakers voice directly into the user's headset via a special receiver. The receiver is used in addition to or instead of the hearing aid. In a large or small venue, one would need to borrow a receiver from the premises and return it after use. For one on one conversations, a portable transmitter and receiver are required. Again, the receiver is used in addition to (with a neckloop) or instead of the hearing aid with borrowed headphones. The portable system can be used between rooms in the house or while walking about. Useful for group tours.
Infrared (IR) Systems - Similar to the FM System, but instead of radio frequency, IR uses a spectrum of light that is invisible to the naked eye to transmit sounds. directly into the user's headset via a special receiver. The receiver is used in addition to (with a neckloop) or instead of the hearing aid (with borrowed headphones). In a large or small venue, one would need to borrow a receiver from the premises and return it after use. It requires an unobstructed path between the source and the receiver. Since light is used to transmit sound, all "sound" is contained in the room where the transmitter is installed. Suited to large and small venues.
Some material on this page was derived from http://www.chha.ca/documents/Universal_Design_and_Barrier-Free_Access.pdf