Brief introduction of public broadcasting and daily maintenance of equipment

As a system problem, public broadcasting must consider the above issues in the system design. Based on the selection of electro-acoustic equipment with good performance, through careful system design, careful system debugging and good sound-building conditions, the sound of the phone is pleasant and natural.

1. Classification of broadcasting system:

The generalized broadcasting system includes two types of sound reinforcement system and sound reproduction system:
1. Sound reinforcement system: The speaker and microphone are in the same sound field, and there are howling, distortion and oscillation caused by acoustic feedback and room resonance. To ensure the stability and normal operation of the system, the highest available system gain is 6dB lower than the critical gain of acoustic feedback self-excitation.
2. Sound reproduction system: There are only sound sources such as tape drives and CD players in the system, no microphones, no possibility of sound feedback, and the sound feedback coefficient is 0, which is a special case of the broadcasting system.

The public address system can be divided into the following categories according to usage:
1) Outdoor broadcasting system The outdoor broadcasting system is mainly used in stadiums, stations, parks, art squares, musical fountains, etc. It is characterized by a large service area and wide space. The background noise is large; the sound propagation is mainly direct sound; the required sound pressure level is high. If there are reflective objects such as high-rise buildings around, and the layout of the speaker is not reasonable, the sound wave will be delayed by more than 50ms after multiple reflections, which will cause Double sounds or multiple sounds, in serious cases, there will be problems such as echo, which affects the clarity of the sound and the positioning of the sound image. The sound effects of outdoor systems are also affected by climatic conditions, wind direction and environmental interference.

2) Indoor broadcasting system Indoor broadcasting system is the most widely used system, including various theaters, stadiums, dance halls, etc. It is very professional, it can be used for non-verbal sound reinforcement, and can also be used for various literary and artistic performances. It has high requirements for sound quality. The system design must not only consider electro-acoustic technical issues, but also involve architectural acoustics. Factors such as the shape of the room have a great influence on the sound quality.

3) Public broadcasting system The public broadcasting system provides background music and radio programs for hotels, commercial buildings, ports, airports, subways, and schools. In recent years, the public address system has also doubled as an emergency broadcast, which can be linked with the fire alarm system. The public broadcasting system has many control functions. Such as constituency broadcasting and all-call broadcasting functions, forced power exchange functions and priority broadcasting rights functions. Loudspeaker loads are heavy and scattered, and transmission lines are long. In order to reduce the transmission line loss, 70V or 100V constant voltage high impedance transmission is generally adopted. The sound pressure requirement is not high, and the sound quality is mainly midrange and midrange and high pitch.

4) Conference system With the increase of domestic and international exchanges, teleconference, video conference and digital conference system (DCN) have developed rapidly in recent years. The conference system is widely used in conference centers, hotels, groups and government agencies. The conference system includes conference discussion system, voting system, simultaneous interpretation system and video conference system. The audio and video (image) systems are required to be synchronized, and all computers are used to control and store meeting materials.

2. Features of public broadcasting

The background music is abbreviated as BGM, which is the abbreviation of Back ground music. Its main function is to cover up the noise and create a relaxed and harmonious atmosphere. If the listener does not listen intently, he cannot distinguish the position of the sound source. This kind of music creates a relaxed and pleasant atmosphere. Therefore, there are two effects of background music, one is to cover up the environmental noise psychologically, and the other is to create an atmosphere suitable for the indoor environment. It is widely used in hotels, hotels, restaurants, shopping malls, hospitals, office buildings and so on.

3. Composition of public broadcasting

No matter what kind of broadcast sound system, basically can be divided into four parts: program equipment, signal amplification processing equipment, transmission line and speaker system.

Program source equipment: Program sources are usually provided for radio broadcasting, CD players and recording decks, in addition to microphones, electronic musical instruments, etc.

Signal amplifiers and processing equipment: including equalizers, preamplifiers, power amplifiers, various controllers, and audio processing equipment. The primary task of this part of the equipment is signal amplification, followed by signal selection. The function and status of the mixer and preamplifier are similar (of course, the function and performance index of the mixer is higher), their basic function is to complete the signal selection and preamplification, in addition, they are responsible for various adjustments of volume and sound effects. And control. Sometimes, in order to better perform frequency equalization and timbre beautification, a graphic equalizer is additionally separately invested. This part is the "control center" of the entire broadcast audio system. The power amplifier amplifies the signal sent from the pre-amplifier or mixer, and then pushes the speaker to play sound through the transmission line.

Transmission line: Although the transmission line is simple, it has different requirements with different systems and transmission methods. For auditoriums, theaters, etc., because the distance between the power amplifier and the speaker is not far away, a low-impedance, high-current direct feeding method is generally used. The transmission line requires a dedicated speaker line. The loss caused by the transmission line is often a high-voltage transmission method. Because the transmission current is small, the requirements on the transmission line are not high.

Loudspeaker system: The loudspeaker system requires the matching of the entire system, and the choice of its position should also be practical. The sound of auditoriums, theaters, dance halls, and speakers generally use high-power speakers; and public broadcasting systems, because of its low sound quality, generally use 3W-6W in ceiling speakers.

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Simple maintenance of public address system equipment

1. The normal working temperature of broadcasting equipment should be generally 18 ℃ ～ 45 ℃. If the temperature is too low, the sensitivity of some machines will be reduced; if it is too high, the components will be easily burned out, or the components will be prematurely aged. Special attention should be paid to cooling and maintaining air circulation in summer.

2. Avoid direct sunlight on broadcasting equipment, and avoid close to heat sources, such as heaters.

3. After the broadcasting equipment is used up, each function key should be reset. If the function key is not reset for a long time, its pulling button spring is under a long-term stress state, it is easy to cause malfunction.

4. Turn the volume potentiometer of the power amplifier to the minimum before switching on or off the power of the equipment. This is one of the most effective protection methods for the power amplifier and the speaker. At this time, the power amplification of the power amplifier is almost zero, at least when it is misused, it will not cause harm to the speaker.

5. When starting from front to back, turn on the CD player first, and then turn on the pre-stage and post-stage. Turn the volume potentiometer of the power amplifier to the minimum when turning on. Turn off the power amplifier first when turning off, so that the amplifier's amplification function is completely turned off. When you turn off the front-end equipment at this time, no matter how big the inrush current is, it will not affect the amplifier and the speaker. When closing the screen, turn the volume potentiometer of the power amplifier to the minimum. Turn it off or turn it on and then turn it off before turning it off.

6. The machine should be used frequently. Commonly used can extend the life of the machine, such as some parts with a motor (recording base, CD player, laser