Public broadcasting (Public Address, referred to as the PA) : by using unit self-administered, in this unit is within the scope of Public service voice broadcast. For business radio, background radio and emergency broadcasting, etc.

Background music and emergency broadcast (Back ground music referred to as BGM), it is mainly used to cover up noise and create a relaxed and harmonious atmosphere, to hear people if not listening, you can't tell the source location, volume is small, it is a kind of creation relaxed and happy atmosphere environment of the music. Therefore, the effect of background music has two, one is the psychological cover environmental noise, 2 it is to create the indoor environment and adapt to the atmosphere.

Public broadcast system including background music and emergency broadcast function, usually together, its object for public places, in the corridor, at the door of the elevator, the elevator car, hall, shopping malls, restaurants, bars, the banquet hall, the village garden installed place such as combined acoustic column or distributed speaker box, usually play background music, when the event of an emergency, strong cutting for emergency broadcast, and use it to command to disperse the crowd.
Control function

Public broadcasting system control function is more, such as selection broadcast and all call broadcasting function, forced switching function and the first broadcast function, etc. Public broadcast system speaker load much and dispersion, transmission line long. To reduce the transmission line loss, generally use 70 v or 100 v rated voltage high impedance delivery. Sound pressure demand is not high, quality in alto and Alt is given priority to. This system with radio microphone and to the public broadcasting speakers generally does not place the same room, so silent feedback problems.
Public broadcast system classification

1. Public broadcast system according to the transmission, signal processing mode can be divided into the following categories:
Traditional public broadcast system

Is through the audio line simulation of the power signal transmission to terminal speaker, with room of power amplifier to the speaker is using high level transmission, general for 100 v or 70 v, its advantage is line loss less, load connection is convenient, just take step-down transformer of speakers and can meet online road.
Digital addressable public broadcast system

The real meaning of digital addressable public broadcast system it audio signals and control signals and communication in all digital domain, has further transmission distance and better transmission effects, especially the audio signal and the control signal are concentrated in a two twisted-pair on transmission, not only greatly save the installation and wiring cost, but also for future system maintenance and system of high reliability offers superior conditions of precedent.
Streaming media (IP) intelligent digital broadcasting

Is based on the Internet and LAN of pure digital network audio broadcasting system, the difference between the traditional analog audio, FM, addressing and CNC radio broadcasting system, streaming media (IP) intelligent digital broadcast system fully compatible with the existing Internet and LAN, the application of TCP/IP protocol without prior wiring, can use the existing campus network or internal LAN; Embedded hardware terminal, can set up independent IP address, but through the multilayer switches, through the host can be arbitrary control each terminal Settings and play, but also in the terminal to select the desired program content; Because of the use of computer technology, the system can include all audio formats, the IP technology, broadcast program content can without any limitation, each terminal can follow one's inclinations play need the contents of the programme. Can completely replace the traditional based on analog or digital intelligent broadcast system, the true realization based on the Internet or LAN IP audio broadcasting function, support broadcasting, live, on demand, etc, the partial products support full-duplex bi-directional interphone, terminal speech, and other functions, and support a wide range of universal application.
2. Public broadcast system according to use function and property can be divided into the following categories:
YeWuXing broadcast system

It is a business and administrative management as the language radio, used in office building, businesses and government organs, schools, railway stations, wharves, airports and other places, usually YeWuXing broadcast by the competent department management;
Service broadcasting system

This is the background music appreciation is given priority to with service character of broadcasting system, and often used in hotel, hotel, bank, securities, parks, squares and large public activity and other places;
Emergency broadcasting system

This is used to meet in the fire as an emergency evacuation guide the requirements of designed such as broadcasting system, usually the broadcasting system and the two systems use combined with the design, first of all should press emergency broadcasting system requirements to determine the system;
Conference system

With the increase of domestic and international exchange in recent years, conference call, video conference and the digital conference system (DCN) development soon, conference system is widely used in the conference center, hotel, group and government authorities. Conference system including meeting to discuss system, decision making system, simultaneous interpretation system and video conference system, request the sound, video (image) system synchronization, all adopt computer control and storage meeting material.
3. Public broadcast system according to the use place can be divided into the following categories:
Outdoor broadcast system

Mainly used in the stadium, station, park, art square, music fountain, etc. It is characteristic of the service area big, broad space. Background noise, Sound transmission to the direct sound is given priority to, Requirements of the sound pressure level is high, if surrounded by tall buildings and reflection objects, speaker layout and is not rational, acoustic by multiple reflection and the formation of more than 50 ms delay of above, can cause double sound or multiple voice, serious problems will appear echo, affect the clarity of the sound and video and acoustic positioning. Outdoor system sound effect by climatic conditions, wind direction and environmental interference and influence.
Indoor broadcasting system

Is the most widely applied system, including all kinds of cinema, stadium, singing and dancing hall, etc. Its specialization is very strong, can nonverbal sound reinforcement, and can be used for all kinds of literature and art performance is used for very tall to the requirement of quality, system design should not only consider electroacoustic technical problems, but also involves architectural acoustics question. Room form factors have great influence on quality.
Public broadcasting system composition

No matter which kind of broadcast sound system, the basic can be as shown in figure 1 shows points four parts: program equipment, signal amplification processing equipment, transmission line and the speaker system.
Program equipment

Usually the traditional such as: DTU - 6300 digital tuner, MPT - 6000/6000 a multimedia player and so on; Intelligent such as: DPC - 9800 digital program control center, DPP - 9300 campus radio player, DPP - 9310 a digital audio broadcast control machine, DPP - 9330 CNC MP3 player, IP digital broadcasting such as: AVH DB - V series IP network digital server software, etc., they are all built-in digital audio source, and can control the related system of the equipment. In addition, a few such as radio, CD player and recording holder and other equipment, in addition to microphone, electronic instruments, etc.;
Signal amplifier and processing equipment

Including equalizer, preamplifier, power amplifier and various control equipment and sound processing equipment, etc. This part of the equipment's first task is to signal amplification, the second is the choice of signal. Mixer and preamplifier function and position of similar (of course mixer function and performance index higher), their basic functions are complete signal selection and preamplifier, in addition to the volume and sound effects in all kinds of adjustment and control. Sometimes in order to better frequency balance and tone beautification, still another separate into graphic equalizer. This part is the whole broadcast sound system of "control center". Power amplifier will preamplifier or mixer delivery of the signal power amplification, again through the line to promote the speaker scream;
Transmission line

Although simple, but as the system and transmission mode of different and have different requirements, generally can be divided into four kinds, such as analog audio circuit, digital twisted-pair cable line, streaming media (IP) data network line, CNC optical fiber line.

In the hall, theater, etc., due to the power amplifier and loudspeaker distance not far, generally USES low resistance large current direct feed way, transmission line require special horn line, and to the public broadcasting system, due to the service area wide, long distance, in order to reduce the transmission line caused by the loss, often adopts high voltage transmission mode, due to the transmission current is small, so the transmission line demand is not high, generally USES ordinary audio line then, belongs to the analog audio line;

Digital addressable public broadcast system generally adopts digital twisted-pair cable for transmission, it is the audio signal and the control signal are concentrated in a two twisted-pair on transmission, not only greatly save the installation and wiring cost, but also for future system maintenance and system of high reliability provides the favourable conditions precedent, with further transmission distance and better transmission effect;

At present most of the schools, companies and other public places have been cloth has a streaming media (IP) data network line (LAN line), for streaming media (IP) public broadcast system is based on this just will flow media (IP) public broadcast system equipment add up went, apply directly to the original streaming media (IP) data network line for transmission, and it does not need to be wiring;

Since in many places such as parks, community and other public broadcasting area area is larger, transmission line is further, transmission mode, can choose CNC optical fiber line to wear lose, transmission distance can reach 20-200 km, so as to solve before public broadcast system without the disadvantages of long distance transmission.
Speaker system

For the whole system matching, and at the same time, the position choice also want to practical, indoor general use smallpox horn, indoor sound column, wall hanging speakers or mounted speaker can, outdoor can use outdoor sound column, lawn special speakers, horn, etc.