background music broadcasting system

Scenic music and public broadcasting
　　Back ground musicBGM (short for BGM), 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.

control function
　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.

Classification of Public Broadcasting Systems
1. The public broadcasting system can be divided into the following categories based on transmission and signal processing methods:

Traditional Public Broadcasting System
The analog power signal is transmitted to the terminal speaker through an audio cable. The power amplifier in the computer room uses high-level transmission to the speaker, usually 100V or 70V. Its advantages are low line loss and easy load connection. Simply connect the speaker with a step-down transformer to the line.

Digital addressable public broadcasting system
The truly 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.

Streaming Media (IP) Intelligent Digital Broadcasting
It is a pure digital network audio broadcasting system based on the Internet and local area network, which is different from the traditional analog audio, FM, addressing and CNC broadcasting systems. The streaming media (IP) intelligent digital broadcasting system is fully compatible with the current Internet and local area network. TCP/IP protocol is applied, without additional wiring, and the existing campus network or internal local area network can be used; Embedded hardware terminals that can set independent IP addresses can be controlled through multi-layer switches, and the settings and playback of each terminal can be freely controlled by the host. Additionally, desired program content can be selected on the terminal; Due to the use of computer technology, the system can be compatible with almost all audio formats. With IP technology, the program content played can be unrestricted, and each terminal can play the required program content as desired. 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. The public broadcasting system can be divided into the following categories based on its usage function and nature:

Business broadcasting system
This is a language broadcast primarily focused on business and administrative management, used in office buildings, commercial buildings, government agencies, universities, stations, docks, airports, and other places. Business broadcasts are usually managed by the competent authorities;

Service Broadcasting System
This is a service-oriented broadcasting system that focuses on appreciating background music, commonly used in hotels, inns, banks, securities firms, parks, squares, and large public events;

emergency broadcast system
This is a broadcasting system designed to meet the requirements of guiding personnel evacuation in emergency situations 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;

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. The public broadcasting system can be divided into the following categories according to the place of use:

Outdoor broadcasting system
Mainly used in sports venues, 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.

Indoor broadcasting system
It is the most widely used system, including various cinemas, sports stadiums, 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.

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.

Program source equipment
Usually traditional ones 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;

Signal amplifiers and processing equipment
Including equalizers, preamplifiers, power amplifiers, various control equipment, 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; 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. However, 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.

speaker system
The matching of the entire system is required, and the selection of its location should also be practical. Indoor speakers such as ceiling speakers, indoor sound columns, wall mounted speakers or suspended speakers are generally sufficient, while outdoor sound columns, lawn specific speakers, horns, etc. can be used outdoors.