How to eliminate the noise caused by improper connection of audio equipment

　　From the perspective of a R&D engineer and a system engineer, we can judge from the following points:

　　1. Impedance matching: In the audio system, almost all devices adopt the jumper mode, that is, the output impedance of the device is designed to be very small, while the input impedance is large. This is because in the system, unless the signal is transmitted remotely, it is generally treated as a short line. Moreover, the signal level is low, which requires that the signal can be transmitted with high quality, and the change of load basically does not affect the signal quality. When the signal source is designed as a constant voltage source, or the load is far greater than the internal impedance of the signal source, the above requirements can be met. In fact, the impedance of professional audio equipment is designed according to the above principles. The equipment interconnection adopts the jumper mode, which is the impedance matching of audio equipment. When designing the sound reinforcement system, that is, when one signal source drives several loads, active or passive sound signal distributor must be used to meet the requirements of equipment impedance matching (if two devices are used, they can generally be directly connected to the output end of the preceding equipment). The power amplifier and the speaker are connected according to the nominal output impedance and the input impedance of the speaker. The output impedance of the power amplifier is 4 Ω and 8 Ω, which can be connected to either a 4 Ω speaker or an 8 Ω speaker. When connected to a 4 Ω speaker, the output power of the power amplifier is greater than that of the 8 Ω speaker. Two 8 Ω loudspeakers can be connected to the output end of the power amplifier in a 4 Ω working state. It must be noted that when speakers are connected in parallel, the impedance will be reduced and the parallel equivalent impedance will not be less than the nominal minimum output impedance of the power amplifier, otherwise the power amplifier will be overloaded and cannot work normally. When 4 Ω load impedance is used, the required transmission line impedance is twice lower than that of 8 Ω. In a high-quality audio system, the transmission impedance at 4 Ω output should not exceed 0.2 Ω (excluding the internal resistance of the amplifier). If the transmission is less than 100m, the cross-sectional area should be halved. It is also required that the contact resistance at both ends of the transmission line is small. When preparing the sound system for a performance, it was found that the noise was high and the connectors at both ends of the transmission line were replaced with better connectors, which significantly reduced the noise.

　　How to eliminate the noise caused by improper connection of audio equipment

　　2. Level matching: When audio equipment is interconnected, level matching is equally important. If the matching is not good, or the excitation is insufficient, or overloading will occur and cause serious distortion, the system will not work properly. To achieve level matching, it is necessary not only to match under the rated signal state, but also not to overload when the signal peaks. The peak factor of high-quality system shall be considered as 10dB at least. Modern audio equipment is designed according to the standard, so only pay attention to the discount selection and system tuning, can meet the level matching requirements.

　　3. Balance and imbalance: audio equipment usually has two connection modes: balance and imbalance. When there is common mode interference, the interference signals received by the two balance terminals have the same value but opposite polarity, so the interference signals can cancel each other on the load of balanced transmission. Therefore, the balanced circuit has good anti-interference ability. Try to use balanced input and output in important performance activities.

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