Group Assistive Listening Devices

If there are several people with hearing loss in a group, a system that "broadcasts" what is being said is preferable to a single user device. There are several kinds of systems that do this. The primary advantage is that multiple people can benefit from these systems; the main disadvantage is that they are expensive and are not as portable as the single user devices. The main varieties include infrared, loop, and FM.

All of these systems include a single or multiple microphones that connect to some sort of central unit. The central unit controls the system and transmits the sound signal much like a radio station. Each user has a receiver that picks up the signal and sends it either to a pair of headphones, or to a hearing aid or CI. If a person with a telecoil-equipped hearing aid is using a loop system, no external receiver is required.

Infrared systems depend on a clear line of sight between the transmitter and the receiver. If someone walks between them, or if a clear line of sight is not available, the infrared systems don't work.

FM and loop systems don't require a line of sight, because the signals they use are able to "bend around" intervening objects. In this sense, they are more versatile.
FM and infrared systems are somewhat portable (often in the same way that a cello is portable), while the loop system are generally permanently installed in a particular room.
Because of these features and limitations, the FM systems tend to be the most versatile.