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Noise problems in professional audio systems
May 16, 2018

In sound systems such as recording and live sound reinforcement, the noise problem is a common and very vexing problem. Usually the more sound systems are formed, or the longer the transmission distance, the greater the background noise of the system, and even make the sound The system cannot perform normal recording or amplification work. The mechanism of noise formation in the sound system is more complicated. Xiao Bian makes an analysis on the main causes and solutions of noise in these sound systems.

 

1. Causes of noise

Environmental spurious electromagnetic radiation interference, such as mobile phones. Interphones and other communications equipment, high-frequency electromagnetic radiation interference, the surrounding environment of the elevator. Air conditioning. Automobile ignition. Welding and other electric pulse radiation, studio lighting control, SCR control equipment The generated radiation will be directly mixed into the transmission signal through the audio transmission line to form noise, or through the housing of the device with poor shielding to interfere with the internal circuit of the machine. The practice shows that in some special occasions, such as the use of SCR The studios of optical equipment, if they have not taken reliable shielding and grounding measures, will be very noisy.

 

2. Power interference noise

External interference of audio equipment, in addition to electromagnetic radiation, the introduction of interference noise in the power supply part will be the main reason for another noise, urban power grid due to a variety of lighting equipment. Power equipment. Control equipment access, forming a very serious Source of interference. For example, lighting control equipment connected to the same power grid, air conditioners, motors, etc., will generate a blade front pulse on the power supply line. Inrush currents, ripple voltages of different frequencies, and power supply lines that enter the audio equipment through the power line, will always Some interference noises cannot be effectively filtered out through the power circuit of the audio equipment and will inevitably form noise inside the equipment. In particular, high-power equipment whose electromagnetic compatibility in the same power grid does not meet the requirements is the main cause of interference with audio equipment. .

 

3. Ground loop noise

In the sound system, the entire system must be well grounded, and the grounding resistance must be less than 4 ohms. Otherwise, the inductive charge generated by the equipment in the sound system due to various radiation and electromagnetic induction will not be able to flow into the earth, thus forming a noise voltage superimposed on Audio signal.

If there is a difference in ground potential due to the difference in grounding resistance between grounds of different devices, or if there is a loop in the interior of the system, ground noise may be caused. When two different audio systems are interconnected, noise may also be generated. The noise is directly caused by the ground lines of the two systems.

 

4. Circuit noise inside the device

Audio equipment has an indicator signal to noise ratio. Due to the electrical noise generated by the internal electronic components, the required specifications can be achieved when a device is operated alone, but the noise will increase cumulatively when multiple devices are connected. In practical applications, some low-grade civil audio equipment may not filter well because of the internal power supply, making the communicative sound of the equipment itself very loud, and sometimes causing serious noise in the sound system.


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