An Assistive listening device (ALD) is used to provide hearing ability for people in a variety of situations. A common usage is to aid people who are hard of hearing. The ALD may be used to help people hear televisions and other audio devices and also to help people hear speech through public address

Public address

A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...

 (PA) systems such as in church or at a lecture.

The assistive listening device is usually used as a system where the audio source is broadcast wireless

Wireless

Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

ly over an FM frequency. The person who is listening may use a small FM Receiver

Receiver (radio)

A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

to tune into the signal and listen at their preferred volume.