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Overview of Public Broadcasting System

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Overview of Public Broadcasting System
Due to the limited energy of natural sound sources (such as speeches, singing, instrument playing, sound playback, etc.), their sound pressure level decays with increasing propagation distance. In addition, the influence of environmental noise limits the propagation distance of the sound source. Therefore, electronic technology - a sound amplification system - must be used in public event venues to amplify the sound source signal, increase the sound pressure level in the audience area, and ensure that each listener can obtain an appropriate sound pressure level.
The Public Address System (PA) is a branch of the sound reinforcement system, which is closely related to factories, schools, hotels, stations, docks, squares, venues, cinemas, sports halls, residential areas, and more.
The public broadcasting system is a systematic project that requires close cooperation between various disciplines such as electronic technology, electroacoustic technology, building sound technology, and acoustic art. The sound effect of the public broadcasting system is not only related to the comprehensive performance of the electroacoustic system, but also closely related to the propagation environment of sound, building acoustics, and on-site tuning. Therefore, the final effect of the public broadcasting system requires a correct and reasonable design and debugging of the electroacoustic system, good sound propagation conditions, and correct on-site tuning technology, which complement each other and are indispensable. In system design, it is necessary to comprehensively consider the above issues. Based on the selection of high-performance electroacoustic equipment, through careful system design, meticulous system debugging, and good sound building conditions, a pleasant and natural electroacoustic sound effect can be achieved.
 
（1） Characteristics of Public Broadcasting System
Background music (BGM for short), its main function is to mask noise and create a relaxed and harmonious atmosphere. If the listener is not attentive, they cannot distinguish the location of the sound source and the volume is low. It is a type of music that creates a relaxed and pleasant atmosphere. Therefore, background music has two effects: one is to psychologically mask environmental noise, and the other is to create an atmosphere that is suitable for the indoor environment.
The public address system includes background music and emergency broadcast functions, usually combined together. Its target is public places, and combined sound columns or dispersed speaker boxes are installed in corridors, elevator entrances, elevator cars, halls, shopping malls, restaurants, bars, banquet halls, community gardens, etc. Background music is usually played, and when an emergency occurs, it is forcibly switched to emergency broadcasting to command the evacuation of crowds.
There are many control functions in the public broadcasting system, such as selection broadcasting and full call broadcasting functions, forced switching function, and priority broadcasting function. The public broadcasting system has a large and dispersed load on speakers, and long transmission lines. To reduce transmission line losses, 70V or 100V constant voltage high impedance transmission is generally used. The sound pressure requirement is not high, and the sound quality is mainly mid to high tones. The microphone used for broadcasting in this system is generally not located in the same room as the speaker used for public broadcasting, resulting in the issue of silent feedback.
 
（2） Classification of Public Broadcasting Systems
1. Public broadcasting systems can be divided into the following categories based on transmission and signal processing methods:
1.1 Traditional Public Broadcasting System: Traditional public broadcasting systems transmit analog power signals to terminal speakers through audio cables. High level transmission is used from the power amplifier in the computer room to the speakers, usually 100V or 70V. Its advantages are low line loss and easy load connection. Simply connect the speakers with step-down transformers in parallel to the line.
1.2 Digital addressable public broadcasting system: The true digital addressable public broadcasting system has audio signals, control signals, and communication all carried out in the digital domain, with longer transmission distances and better transmission effects. Especially by concentrating audio signals and control signals on a two core twisted pair cable for transmission, it not only greatly saves installation and wiring costs, but also provides a prerequisite for future system maintenance and high reliability of system operation.
1.3 Streaming media (IP) intelligent digital broadcasting: Streaming media (IP) intelligent digital broadcasting is a pure digital network audio broadcasting system based on the Internet and local area network, which is different from the traditional broadcast systems of analog audio, FM, addressing and numerical control broadcasting. The streaming media (IP) intelligent digital broadcasting system is fully compatible with the current Internet and local area network. It uses TCP/IP protocol and can use the existing campus network or internal local area network without additional wiring; Embedded hardware terminals are capable of setting independent IP addresses, and can control the settings and playback of each terminal through multi-layer switches and hosts. They can also select the desired program content on the terminal. Due to the use of computer technology, the system is compatible with almost all audio formats. With IP technology, the program content can be played without any restrictions, and each terminal can play the desired program content at will. It can completely replace the traditional intelligent broadcast system based on analog or digital, truly realize the IP audio broadcast function based on the Internet or LAN, support broadcast, live broadcast, on-demand and other ways, and support a wide range of popular applications.
2. Public broadcasting systems can be divided into the following categories based on their usage functions and nature:
2.1 Business Broadcasting System: This is a language broadcasting system mainly focused on business and administrative management, used in office buildings, commercial buildings, offices, universities, stations, docks, airports and other places. Business broadcasting is usually managed by the competent department;
2.2 Service Broadcasting System: This is a service-oriented broadcasting system that focuses on enjoying background music and is commonly used in hotels, inns, banks, securities, parks, squares, and large public events;
2.3 Emergency Broadcasting System: This is a broadcasting system designed to meet the requirements of guiding personnel evacuation in emergency events such as fires. Usually, this broadcasting system is combined with the above two systems. When designing a combined system, the system should first be determined according to the requirements of the emergency broadcasting system;
2.4 Conference System: With the increasing domestic and international exchanges, telephone conferences, video conferences, and digital conference systems (DCN) have developed rapidly in recent years. Conference systems are widely used in conference centers, hotels, groups, and government agencies. The conference system includes a conference discussion system, a voting system, a simultaneous interpretation system, and a video conference system. It requires synchronization of audio and video (image) systems, all of which are controlled and stored by computers for conference materials.
3. Public broadcasting systems can be divided into the following categories according to their usage locations:
3.1 Outdoor Broadcasting System: The outdoor broadcasting system is mainly used in sports stadiums, stations, parks, art squares, music fountains, etc. Its characteristics are a large service area and spacious space. High background noise; Sound propagation is mainly through direct sound; The required sound pressure level is high. If there are high-rise buildings or other reflective objects around, and the layout of the speakers is not reasonable, the sound waves will be reflected multiple times to form a delay of more than 50ms, which will cause double or multiple sounds, and in severe cases, echo and other problems, affecting the clarity of the sound and the localization of the sound image. The sound effect of outdoor systems is also affected by climate conditions, wind direction, and environmental interference.
3.2 Indoor Broadcasting System: Indoor broadcasting system is a widely used system, including various cinemas, sports venues, dance halls, etc. It has strong professionalism and can be used for both non-verbal sound amplification and various cultural performances. It has high requirements for sound quality, and system design should not only consider electro acoustic technology issues, but also involve architectural acoustics issues. The shape of the room and other factors have a significant impact on sound quality.
 
（3） Composition of Public Broadcasting System
Regardless of the type of broadcasting sound system, it can be basically divided into four parts as shown in Figure 1: program source equipment, signal amplification and processing equipment, transmission lines, and speaker system.
1. Program source equipment: Program sources are usually traditional devices such as DTU-6300 digital tuner, MPT-6000/6000A multimedia player, etc; Intelligent devices such as DPC-9800 digital program control center, DPP-9300 campus radio player, DPP-9310A digital audio broadcasting control machine, DPP-9330 CNC MP3 player, etc., all have built-in digital audio sources and can control related systems. In addition, there are some equipment such as radio broadcasting, CD players, and recording booths, as well as microphones, electronic instruments, etc;
2. Signal amplifiers and processing equipment: including equalizers, preamplifiers, power amplifiers, various control devices, and audio processing equipment. The primary task of this equipment is signal amplification, followed by signal selection. The functions and positions of a mixing console and a preamplifier are similar (of course, the functions and performance indicators of a mixing console are higher). Their basic functions are to complete signal selection and preamplifier, as well as to make various adjustments and controls to volume and sound effects. Sometimes, in order to achieve better frequency balance and timbre beautification, a separate graphic equalizer is also used. This part is the "control center" of the entire broadcast audio system. The power amplifier amplifies the signal sent by the preamplifier or mixing console, and then drives the speaker to produce sound through the transmission line;
3. Transmission lines: Although transmission lines are simple, they have different requirements depending on the system and transmission method. They are generally divided into four types, such as analog audio lines, digital twisted pair lines, streaming media (IP) data network lines, and CNC fiber optic lines.  
For auditoriums, theaters, etc., due to the short distance between power amplifiers and speakers, a low impedance high current direct feeding method is generally used, and dedicated speaker lines are required for transmission lines. For public broadcasting systems, due to the wide service area and long distance, high-voltage transmission methods are often used to reduce losses caused by transmission lines. Due to the low transmission current, the requirements for transmission lines are not high, and ordinary audio lines are generally used, which belong to analog audio lines;
Digital addressable public broadcasting systems generally use digital twisted pair cables for transmission. It concentrates audio signals and control signals on a two core twisted pair cable for transmission, which not only greatly saves installation and wiring costs, but also provides a prerequisite for future system maintenance and high reliability of system operation, with longer transmission distance and better transmission effect;
At present, most schools, companies, and other public places have installed streaming media (IP) data network lines (LAN lines). For streaming media (IP) public broadcasting systems, simply add the streaming media (IP) public broadcasting system equipment on this basis, and directly use the original streaming media (IP) data network lines for transmission without the need for additional wiring;
Due to the large area and long transmission lines of public broadcasting areas in many places such as parks and residential areas, CNC fiber optic lines can be used for transmission, with a transmission distance of up to 20-200KM, thus solving the problem of traditional public broadcasting systems being unable to transmit over long distances.
4. Speaker system: The speaker system requires a matching of the entire system, and the selection of its location should also be practical. Indoor speakers generally use ceiling speakers, indoor sound columns, wall mounted speakers, or suspended speakers, while outdoor sound columns, lawn specific speakers, horns, and so on can be used outdoors.

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