Audio system signal transmission, what problems should be paid attention to?

　　Professional audio systems are composed of many different functional devices. After designing the audio system according to the use requirements and selecting the equipment used, these discrete devices should be connected according to the design requirements to form a complete set of audio systems that can achieve the design requirements. For a fixed installation system, the equipment should be installed in a cabinet, and all system connections should be fixedly installed in accordance with certain standards and specifications. For mobile systems, such as temporary installations such as concerts and outdoor performances, effective temporary fixing measures should be taken for equipment and cables to ensure their safety.

　　The connection and installation of the audio system involves many engineering issues, including the design and construction of the audio control room, the pipeline engineering of the audio system cable, and the power supply of the system. Here are some issues that need to be paid attention to in the transmission of audio system signals.

　　1. Impedance matching

　　The signal input port is also the load of the signal output port, and the impedance matching between them needs to be within the range to meet its requirements, which generally depends on the design requirements of the signal output device. In order to achieve the best transmission state of the audio electrical signal, the impedance of the signal input interface must meet the impedance matching requirements of the signal source output interface to its load, otherwise, it will affect the working state of the audio equipment and cause distortion of its output signal. In severe cases, there is even a risk of damaging the audio source equipment.

　　Theoretically, when the output impedance is equal to its load impedance, the transmission efficiency of the signal is the highest. However, if the output impedance is greater than the load impedance, most of the signal power will be lost on the signal output circuit, which is obviously not conducive to signal transmission. Therefore, audio equipment is usually designed so that the input impedance is greater than the output impedance.

　　The connection of general audio equipment, as long as the load impedance is greater than the impedance of the signal output end, can make it work normally. However, the input impedance of the audio equipment cannot be designed to be too high or too low. If it is too high, it will reduce the anti-interference of its feeder. If it is too low, it will cause its frequency response index to decrease.

　　2. Signal transmission level

　　The purpose of the audio system connection is to transmit signals. The optimal state of audio signal transmission requires that the level value output by the signal source must be greater than or equal to the sensitivity of the input interface. Otherwise, the signal-to-noise ratio index of the signal will deteriorate. The gain of the line input and output circuits on professional audio equipment is generally set at 0dB, that is to say, the equipment neither amplifies nor attenuates the level of the input or output signal, so that it can be maintained during the transmission process. Its level value remains unchanged, which is mainly to ensure that the adjustment of the level control unit can be numerically guaranteed.

　　In the system connection, attention should be paid to the matching of output and input levels. Otherwise, clipping distortion may be caused, or the excitation signal may be insufficient, resulting in a decrease in the signal-to-noise ratio of the entire system. Usually the connections between audio equipment (mixers, peripherals, amplifiers) are at line level to transmit signals. There are generally two line standards, one is +4dB (1.228V), and the other is 0dB (0.775V). The line level of the equipment used in the system should be unified, so that it will be more convenient to adjust and use. In addition, some sound processing equipment, especially the effector, in order to take into account the needs of electro-acoustic musical instruments and professional sound systems, the interface level conversion function is set. -10dB, -20dB several gears, when using the sound reinforcement system, you should pay attention to adjust it to +4dB gear.

　　3. Weak signal connection

　　The input and output terminals of professional audio equipment are unbalanced, transformer balanced, and differential balanced. Signals can be fed directly between balanced and balanced, unbalanced and unbalanced ports; in demanding occasions, between balanced and unbalanced ports, special converters are required to connect to each other. Converters generally include passive transformer converters, half-voltage converters and active differential amplifier converters.

　　In some occasions with low requirements, the unbalanced terminal and the balanced terminal of the signal can still be fed directly. The wiring method is: the hot terminal of the balanced terminal is connected to the signal terminal of the unbalanced terminal, and the cold terminal of the balanced terminal is connected to the unbalanced terminal. The ground terminal of the balanced terminal is connected to the shielding layer of the signal feeder.

　　In addition to the power transmission between the power amplifier and the speaker, in order to improve the anti-interference ability of the system and ensure the signal-to-noise ratio, the signal connection in the professional audio system should be transmitted in a balanced way as much as possible. Professional audio equipment generally also provides balanced input and output functions.

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