Today's public broadcasts broadcast background music, publicity, paging broadcasts, and emergency broadcasts of fire accidents. This is a highly versatile broadcast system that must have the following features and technical requirements:
     1. Play background music and play paging
     Background music is abbreviated as BGM (BackGroundMusic), which is used to cover the environmental noise of public places and create a relaxed and pleasant atmosphere. The average sound pressure of background music is around 60 to 70 db.
     When playing a paging broadcast in background music, a beep or a bell should be provided to remind the public.
     2. Emergency broadcast
     In the past, the emergency broadcast system was combined with the fire alarm system as a stand-alone system, but it was later found that because the emergency broadcast system did not have to be highly reliable for a long time, it was often no problem when it was tested normally, but it became dumb when it was officially used. The fire alarm system is now integrated with the background music system to form a highly versatile public address system.
     3. When the priority broadcast right function occurs, the fire broadcast signal has the highest priority broadcast right, that is, the fire broadcast signal can automatically interrupt the background music and paging to find people and other broadcasts.
     4. Constituency broadcast function When a fire alarm occurs in the building, in order to prevent confusion, only broadcast to the fire zone and its adjacent areas, command evacuation and organize for help. This selection function should have both automatic selection and manual selection to ensure reliable execution of instructions.
     5, forced switching function When playing background music, the input status of each speaker load is usually different, and some are in a small volume state. Some are in the off state, but in the emergency broadcast, the input state of each speaker will be changed to the maximum full volume state, that is, the volume is forcibly switched by the remote command.
     6. The fire duty room must have an emergency broadcast console. This sub-control station should be able to remotely control the startup and shutdown of the public address system. The sub-console microphone has priority playing rights, and the sub-control has strong switching rights and selection broadcasting rights.
Application of public address system
     1. Campus public broadcasting system The campus broadcasting system is widely used and a broadcasting system. Campus broadcasting is a tool for school information dissemination. It has gone through decades of history. With the development of science and technology, from electronic tubes to Integrated circuits, from phonographs to CDs, have undergone several revolutions, but their technical level and grades are uneven. Basically, they are based on constant voltage amplifiers plus terminal speakers or tweeters, and single-channel audio signal transmission. There are many shortcomings in actual use and work. With the continuous maturity of FM technology in campus broadcasting in recent years, it has unparalleled advantages over traditional broadcasting methods, and its functions are constantly improving. It has gradually replaced traditional broadcasting methods and has become the main realization of current campus broadcasting. the way. The new campus broadcasting system provides intelligent centralized management and control of various peripherals (such as recorders, CDs, MDs, transceivers, and digital audio hard disks). The program content and program length can be edited according to the requirements of the school. The setting time is set in advance, and the PC on duty computer can automatically manage the whole process of broadcasting, and automatically broadcast according to the set program to ensure the integrity, accuracy and punctuality of the program, thereby preventing the phenomenon of interrupting the broadcast for no reason. Conventional radio programs, such as radio gymnastics, songs, music ringing, etc., can be broadcast unattended. The system has very high reliability, the system transmission network signal noise is low, there is no power matching and voltage matching requirements in the system network, the failure of a single speaker does not affect the whole system work, and the whole machine automatically turns off when there is no signal. The speaker automatically turns on when the start signal is received or when the power-on command is received. Unattended.
     2. Hotel, hotel public address system For a hotel, hotel public address system, room broadcast system is essential. The room broadcast system usually has to set up multiple broadcast signals for the guests to choose to listen to. For star-rated hotels and hotel room broadcast systems, there are 2 sets of broadcast signals and 4 sets of broadcast signals. There are several ways to implement room broadcasts:
     (1) In the machine room, a set of broadcast program signals is amplified by a power amplifier, and multiple sets of broadcast program signals are transmitted by the multi-core cable; at the terminal, the guest selects to listen to the broadcast program through the control panel of the room bedside cabinet.
     (2) In the computer room, multiple sets of broadcast program signals are mixed and amplified by multiple RF modulators, and one RF cable is used for signal transmission; at the terminal, the guest selects to listen to the broadcast program through the FM receiver installed in the control panel of the bedside table of the guest room. .
     (3) In the computer room, multiple sets of broadcast program signals are mixed and amplified by multiple radio frequency modulators, incorporated into the cable TV redundant channel, and transmitted with the cable television cable; at the terminal, the guest selects to listen to the broadcast program through the television.
     (4) In the computer room, multiple sets of broadcast program signals are mixed and amplified by multiple radio frequency modulators, preset address codes, and signals are transmitted by using one RF cable; at the terminal, the guests receive FM transmission through the control panel of the bedside cabinet of the guest room. The machine selects the address code to listen to the broadcast program.
     3. Hospital Broadcasting System The hospital's broadcasting system is a publicity, education and entertainment stage with many listeners and great influence. How to effectively manage and effectively apply is a problem that needs to be solved. Usually, hospital-level broadcasts must have special personnel on duty management equipment and playback work, as well as maintenance of outdoor lines. The workload is large, and it is not convenient for the unified management of superior authorities.
Modern hospital broadcasts may require different programs to be broadcast at different times in different areas of the broadcast network. The unified production and reasonable management of each broadcast network program source have different levels of demand. For example, if different programs (health care common sense) and individuals want to listen to different programs in different wards, rooms or beds, they can play separate controls as needed.
     4. Metro Public Broadcasting System The subway broadcasting system is a special subsystem in the subway communication system. It plays an important role in subway organization, passenger transportation services, disaster prevention and rescue, and equipment maintenance. In different areas of the subway station, different service terms and related precautions are broadcast for ticket sales, ticket checking, pit stop, waiting, boarding, boarding, transfer, etc., in order to provide various services, maintain the order of the station, and effectively guide passengers. By car, first and then, the train stop time is shortened, the train is punctual, the conditions are created, and other job broadcasts can be provided for the station staff; the dispatching command and the yard shunting are carried out in the subway work sites such as the depot and the tunnel section. Providing safety notices and notifications, etc. for vehicle commissioning, equipment maintenance, line maintenance, power supply rails, power outages, equipment delivery, etc.; when major events, assemblies, events, festivals, etc. cause sudden changes in subway passenger flow, as an emergency The important means of passenger transport organization provides guarantee for ensuring the safety of large passenger flow operation organizations and passengers; when emergencies such as accidents and disasters, it is an important tool for emergency evacuation and command disaster relief.
Providing functionally advanced and advanced working tools for metro passenger transport, traffic, disaster prevention, equipment maintenance and other departments, improving the quality of metro passenger transport services and handling emergencies.
     5. Public broadcasting systems for large shopping malls and supermarkets In general, public broadcasting systems in large shopping malls and supermarkets should also have the function of fire emergency broadcasting system. Under normal circumstances, the public broadcasting system not only has the function of playing the background music broadcasting system such as background music and broadcast notification, but also can realize the emergency broadcast of the manual selection in the accident area when encountering the fire alarm.
In the public broadcasting system of large shopping malls and supermarkets, the program source is usually set to three: CD player, dual card recording station and broadcast microphone. The CD player uses a multi-disc CD player, and multiple CDs are pre-loaded. All the tracks can be played in advance for playing background music. The recording deck uses a dual-card recording dock. The dual-card can work cyclically, playing background music tapes, and can also be used for broadcast notifications for temporary recording.
The broadcast microphone uses a desktop gooseneck microphone, which is easy to operate, and has a built-in bell generator. It can emit a crisp bell before speaking to remind the audience, mainly for broadcast notification. Many large shopping malls and supermarkets are single-storey buildings. According to the requirements of China's fire protection system, multiple fire shutters must be installed in the inner area. When designing large-scale shopping malls and supermarket public broadcasting systems, they must also follow the relevant regulations for broadcasting zones according to internal fire prevention areas. .