1, Classification of broadcasting systems
The broad broadcasting system includes two categories: amplification system and playback system:
① Sound reinforcement system
The speaker and microphone are in the same sound field, and there are howling, distortion, and oscillation phenomena caused by sound feedback and room resonance. To ensure system stability and normal operation, the maximum available system gain is 6dB lower than the critical gain for acoustic feedback self-excitation.
② Sound system
In the system, there are only sound sources such as magnetic tape drives and optical disc players, without microphones, and there is no possibility of sound feedback. The sound feedback coefficient is 0, which is a special case of the broadcasting system.
2, Public broadcasting systems can be divided into the following categories based on their purpose
① Outdoor broadcasting system
The outdoor broadcasting system is mainly used in sports venues, stations, parks, art squares, music fountains, etc. Its characteristics are a large service area and wide space. High background noise; Sound propagation is mainly through direct sound; The required sound pressure level is high. If there are reflective objects such as high-rise buildings around, and the speaker layout is not entirely reasonable, the sound wave will form a delay of more than 50ms after multiple reflections, which can cause double or multiple sounds. In severe cases, echo and other problems may occur, affecting the clarity and image positioning of the sound. The sound effect of outdoor systems is also affected by climate conditions, wind direction, and environmental interference.
② Indoor broadcasting system
Indoor broadcasting system is the most widely used system, including various cinemas, sports venues, dance halls, etc. It has strong professionalism and can be used for both nonverbal sound reinforcement and various artistic performances. The requirements for sound quality are high, and the system design not only needs to consider electroacoustic technology issues, but also involves architectural acoustics issues. The shape of a room and other factors have a significant impact on sound quality.
③ Public Broadcasting System
The public broadcasting system provides background music and radio programs for hotels, shopping malls, ports, airports, subways, and schools. In recent years, the public broadcasting system has also been used for emergency broadcasting and can be linked with the fire alarm system. The public broadcasting system has many control functions. Such as the functions of selective broadcasting and full call broadcasting, mandatory power exchange, and priority broadcasting rights. The speaker has a large and scattered load, and a long transmission line. To reduce transmission line losses, high impedance transmission with a fixed voltage of 70V or 100V is generally adopted. The sound pressure requirement is not high, and the sound quality is mainly in the middle and high notes.
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.The conference system is 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. Require synchronization of audio and video (image) systems, all controlled and stored by computers for conference materials.
3, The characteristics of broadcasting systems
Background music, abbreviated as BGM, is an abbreviation for Back ground music. 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. It is widely used in hotels, hotels, restaurants, shopping malls, hospitals, office buildings, and other areas.
4, Composition of Broadcasting Sound System
Regardless of the type of broadcasting sound system, it can be basically divided into four parts: program equipment, signal amplification and processing equipment, transmission lines, and speaker system.
① Program source equipment
The program source is usually provided by devices such as radio broadcasting, CD players, and recording cartridges, as well as microphones, electronic instruments, and so on.
② Signal amplifiers and processing equipment
Including equalizers, preamplifiers, power amplifiers, various controllers, and audio processing equipment. The primary task of this equipment is signal amplification, followed by signal selection. The function and status of a mixing console and a preamplifier are similar (of course, the function and performance indicators of a mixing console are higher). Their basic function is to complete signal selection and preamplification, in addition to being responsible for various adjustments and controls of volume and sound effects. Sometimes, in order to achieve better frequency balancing and timbre beautification, a separate graphic equalizer is also added. This part is the "control center" of the entire broadcasting audio system. The power amplifier amplifies the signal sent by the preamplifier or mixing console, and then drives the speaker to play sound through the transmission line.
③ Transmission line
Although the transmission line is simple, it has different requirements depending on the system and transmission method. For auditoriums, theaters, etc., due to the short distance between power amplifiers and speakers, low resistance and high current direct feeding methods are generally used. The transmission line requires dedicated speaker 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 small transmission current, the requirements for transmission lines are not high.
④ Speaker system
The speaker system requires the matching of the entire system, and the selection of its position should also be practical. Auditoriums, theaters, and dance halls typically use high-power speakers for sound quality, while public broadcasting systems typically use 3W-6W ceiling speakers due to their low sensitivity to sound quality.
5, Design process of public broadcasting engineering system
The design of public broadcasting systems usually starts from the sound field (i.e. the placement of speakers), and then progresses backwards to power amplifiers, sound processing systems, mixing consoles, microphones, and other sound sources. This gradual backward design step is very inevitable. Because sound field design is the foundation for meeting system functions and sound effects, it involves the selection of speaker systems, sound supply schemes, and signal pathways. Only by determining the speaker system can the calculation of power amplifier driving power and the determination of driving signal path be carried out, and then the signal processing scheme and selection of mixing console can be further determined based on the distribution scheme of driving power.