Public Address System (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals.
PA SYSTEM BASICS
PA systems usually consist of two loudspeaker cabinets, each of which usually contains one large speaker and a smaller “tweeter” speaker or horn for higher frequencies. They’re typically passive speakers, which means they require amplification. This is why most systems include a power amp so that everything receives the power it needs.
PA systems also include a powered mixer, which is like the central nervous system of your PA (similar to a receiver in a stereo system). It will have between four and 24 inputs or channels, and controls for tone, volume, and maybe some echo effects.
Those channels take in and process electrical audio signals from various microphones, instruments, or audio devices before amplifying them to wattage strong enough to drive speakers.