During stage performances, the most fearful thing is the noise from the stage lighting and sound! This is a very vexing problem. The noise generated by a sound system is not the same. It may come from many aspects. The sound engineer should analyze and judge the more complex situations and deal with them respectively. Generally, noise may come from three aspects: First, improper connection of the equipment; Second, the inherent noise of the equipment itself; Third, interference noise from the power supply. The specific processing methods are introduced below.
Eliminate noise caused by improper connections of devices
There are common equipment interconnection problems in Audio Systems. If the connection is improper, it will cause the system indicators to drop and generate noise. In severe cases, it may even cause the equipment to not work properly. Please do the following when connecting:
1. Impedance matching: In the stage sound system, almost all equipment adopts the crossover method, that is, the output impedance of the equipment is designed to be very small and the input impedance is very large. This is because in the system, unless the signal is transmitted over a long distance, it is generally treated as a short line. Moreover, the signal level is low, requiring the signal to be transmitted with high quality, and changes in the load basically do not affect the quality of the signal. When the signal source is designed as a constant voltage source, or the load is much 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, and the equipment interconnection adopts the crossover method. This is the impedance matching of audio equipment. When designing a sound reinforcement system, it is generally not necessary to consider impedance issues. However, when the output of one device needs to be connected to multiple devices, that is, when one signal source drives several loads, an active or passive audio source signal distributor must be used to meet the device impedance matching requirements (if it is two devices, Generally, it can be directly connected to the output end of the front-end device).
The power amplifier and speakers are connected according to the nominal output impedance and the input impedance of the speakers. The output impedance of the power amplifier is 4Ω and 8Ω. It can be connected to 4Ω speakers or 8Ω speakers. When connected to a 4Ω speaker, the output power of the power amplifier is greater than when it is connected to an 8Ω speaker. Two 8Ω speakers can be connected in parallel to the output of the power amplifier, working in 4Ω. It must be noted that when speakers are connected in parallel, the impedance will decrease, and the parallel equivalent impedance must not be less than the nominal minimum output impedance of the power amplifier, otherwise the power amplifier will be overloaded and unable to work properly. When using a 4Ω load impedance, the required transmission line impedance is twice as low as that of 8Ω.
In a high-quality audio system, the transmission impedance at 4Ω output should not exceed 0.2Ω (excluding the internal resistance of the amplifier). If the transmission is less than 100m, the cross-section is required to be not less than 9mm2. If you want to reduce its cross-section, you need to use 8Ω output instead of 4Ω output. At this time, the cable cross-sectional area can 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, I found that the noise was high. I replaced the connectors at both ends of the transmission line with better gold-plated connectors, and the noise was significantly reduced.
2. Level matching: When interconnecting stage audio equipment, level matching is equally important. If the matching is not good, there may be insufficient excitation, or overload may occur, resulting in severe distortion, which will cause the system to fail to work properly. To achieve level matching, it is necessary not only to match the rated signal signal state, but also to avoid overloading when the signal peaks. A good system crest factor should be considered at least 10dB.
3. Balanced and unbalanced: Stage audio equipment usually has two connection methods: balanced and unbalanced. When there is common mode interference, since the interference signals received on the two balanced terminals are similar in value but opposite in polarity, the interference signals can cancel each other out on the load of balanced transmission. Therefore, the balanced circuit has better anti-interference ability. In important performance activities, try to use balanced input and output.