The noise problem of professional audio system

　　In professional audio systems such as live sound reinforcement, the noise problem is a widespread and very headache problem. Generally, the more the audio system is composed, or the longer the transmission distance, the greater the background noise of the system, and even the professional audio system It is impossible to perform normal recording or amplification work, and the mechanism of professional audio system noise is more complicated. Now we will analyze and discuss the main causes and solutions of these professional audio system noises.

　　1 Causes of noise

　　Environmental stray electromagnetic radiation interference, such as high-frequency electromagnetic radiation interference of communication equipment such as mobile phones, walkie-talkies, elevators, air conditioners, car burning, electric welding and other electrical pulse radiation in the surrounding environment. The radiation that occurs will be directly mixed into the transmission signal through the audio transmission line to form noise. Or pass through the casing of the poorly shielded equipment to disturb the internal circuit of the machine. The practice indicates. In some special occasions, such as many use thyristor tuning In the studio of optical equipment, if reliable shielding and grounding measures are not adopted, the noise will be severe.

　　2 Power disturbance noise

　　The external disturbance of professional audio equipment, in addition to the electromagnetic radiation method, the introduction of disturbance noise from the power supply part will be another main cause of noise. Due to the joint access of various lighting equipment, power equipment and control equipment, the urban power grid constitutes a very serious problem. Source of disturbance. For example, lighting control equipment, air conditioners, motors and other equipment connected to the same power grid will generate sword pulses, surge currents, and ripple voltages of different frequencies on the power line, which will enter the power supply of professional audio equipment through the power line. There will be a part of disturbing noise that cannot be effectively filtered out by the power circuit of professional audio equipment, and it will inevitably constitute noise inside the equipment, especially high-power equipment that does not meet the electromagnetic compatibility requirements in the same power grid, which is disturbing professional audio equipment. The main reason.

　　3 Noise from the ground loop

　　In the professional audio system, it is necessary to require a good grounding of the entire system, and the grounding resistance must be less than 4 ohms. Otherwise, the induced charges generated by the equipment in the professional audio system due to various radiation and electromagnetic induction will not be able to flow into the ground, and then constitute noise The voltage is superimposed on the audio signal.

　　If there is a ground potential difference between the ground wires of different devices due to the difference in ground resistance, perhaps there is a loop in the internal ground of the system, which will cause ground noise. When two different professional audio systems are interconnected, noise may also occur. The noise is directly caused by the ground wires of the two systems.

　　4 Circuit noise inside the device

　　Professional audio equipment has an indicator-signal-to-noise ratio. Due to the electrical noise generated by the internal electronic components, a single device can achieve the required index, but when multiple devices are connected, the noise will increase cumulatively. In practice, some low-grade civil audio equipment will have a bad internal power supply filter, which will make the communication sound of the equipment itself very loud, which sometimes constitutes very severe noise in the professional audio system.

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