Public Address / Talk back System:
A Public Address (PA) system is a collection of audio equipment that allows broadcasts over a designated area. Often found in schools and office buildings, PA systems can be used for general announcements or emergency information, providing a simple way to get information out quickly. PA systems can be basic or advanced, and people can customize them to fit a variety of needs.
Basic PA systems are comprised of loudspeakers placed in convenient locations, an amplifier to increase the sound, and a mixer that adjusts audio levels. The user speaks into a microphone, and the sound is transmitted through connected cables, or a wireless system, out through the speakers. Some systems also include microphones or intercoms near the speaker locations, allowing the listener to reply to the central location. These responses are not broadcast to the entire system, however, but only to the main user area.