The public address system called PA system (Public Address) is widely used in railway stations, airports, hotels, commercial buildings, hospitals and various buildings to provide background music and radio programs, public broadcasting system in recent years and also serves as an emergency broadcast. Its main purpose is to promote its business and affairs policy broadcasting, emergency broadcasting public broadcasting background music and radio paging, fire accidents and unexpected incidents.
　　Today's public broadcasting emergency broadcast set to play background music, propaganda, paging, radio and fire accidents as a whole. This is a highly versatile broadcasting system, this versatile public address system must have the functional and technical requirements of the following:
1, play background music and paging player
　　Background music Acronym BGM (Back Ground Music), its role is to cover up the ambient noise in public places, to create a relaxed atmosphere. Background music average sound pressure at around 60 to 70db. Paging broadcast in the background while playing music, it should be provided or bells buzz tone to alert the public.
2, emergency broadcast
　　Emergency broadcast system combines past and fire alarm systems together, as a stand-alone system, but later found that the emergency broadcast system, the culmination of the long-term reliability problems often do not have it usually do not have a problem during the test, but in official use has become mute, so now regard the fire alarm system integration and background music systems together to form a highly versatile public address system.
3, the priority right to broadcast function
　　In case of fire, fire radio signal with the highest level of priority broadcasting rights, namely the use of fire radio signal can be automatically interrupts the background music and paging someone of broadcast.
4, broadcast function selection
　　When the fire alarm building, in order to prevent confusion, only the fire zone and adjacent regional broadcasting, directing and organizing the evacuation help matters. Two artificial constituency and functional constituency that should be automatic selection, to ensure reliable execution of instructions.
5, forced switching function
　　Enter the state of play background music of each speaker load is usually not the same, some in small volume status. Others are in the closed state, but in an emergency broadcast, the input status of each speaker will be converted to full volume the largest state in which the volume of mandatory instruction by remote control switch.
6, fire duty must have
　　Emergency broadcast console, this sub-control station should be able to boot the remote public address system, shut down, sub-console microphone broadcast rights have priority, sub-control switch with strong rights and broadcast rights and other constituencies.