Analysis and treatment of whistling in microphone sound system.The bar needs sound equipment

　　1. The cause of howling

　　Once the sound system whistle occurs, it will cause the volume of the microphone channel to be unable to be turned up. After turning up the volume, the howling is very serious, which will have a bad impact on the live performance. When the critical point of howling is reached, the microphone will sound louder The sound of ringing phenomenon has a sense of reverberation, which destroys the sound quality; in severe cases, the speaker or power amplifier is burned out due to the strong signal.

　　It is not uncommon for the tweeter of the speaker to be burnt due to whistling, because in the whistling state, the strong signal will cause the power amplifier to clip (top-cut) distortion and generate a large number of high-frequency harmonics. If the tweeter cannot withstand such a Powerful high-frequency signals will cause the voice coil to be burned; in addition, in the howling state, if the output of the power amplifier is overloaded, it may also be burned.

　　Howling problem exists only in the sound reinforcement system, which is an abnormal phenomenon that often occurs in the sound reinforcement system. When using a microphone to pick up sound in a sound reinforcement system, since it is impossible to take sound isolation measures between the pickup area of the microphone and the sound reproduction area of the speaker, the sound of certain frequencies is too strong to cause self-excited oscillation of the acoustic and electrical signals, resulting in howling. . For howling to occur, three conditions must be met:

　　1. The microphone and the speaker are used at the same time;

　　2. The sound of the audio broadcast can be transmitted to the microphone through the space;

　　3. The sound energy from the speaker is large enough and the pickup sensitivity of the microphone is high enough.

　　2. How to suppress howling

　　Howling is an acoustic problem unique to the sound reinforcement system and cannot be completely eliminated. In practice, audio experts have summed up many methods to suppress the howling of the audio system. By taking effective measures and using some electro-acoustic equipment, the purpose of suppressing, reducing and eliminating howling can be achieved. The idea is to avoid There are three conditions for the sound system to whistle at the same time.

　　1. Make the sound of the speaker not easily transmitted to the microphone

　　a. The microphone is far away from the speaker.

　　b. Decrease the volume of the microphone. If the volume of the microphone is too high, the probability of ringing will increase, so reduce the volume in time to avoid howling. In addition, if you want to hold or wear the microphone through the speaker, you should also pay attention to controlling the volume, otherwise it will cause serious howling due to the distance.

　　c. Make reasonable use of the directional characteristics of speakers and microphones

　　Both the microphone and the speaker are directional. If the use position of the microphone is not in the radiation area of the speaker, the sound of the speaker will not be easily transmitted to the microphone. Similarly, if the speaker is not in the pickup area of the microphone, it will be difficult for the microphone to pick up the sound of the speaker. sound. Therefore, by properly adjusting the angle of the speaker, keeping it away from the sound-emitting area of the speaker when using the microphone, or keeping the sound radiation area of the speaker from overlapping with the area where the microphone is used, howling can be suppressed.

　　2. Use electro-acoustic equipment to suppress howling

　　a. Frequency shifter.

　　Changing the sound frequency by a frequency shifter can destroy the conditions for howling, thereby suppressing howling. However, the device has certain limitations and is not suitable for use in singing and musical instruments. It can increase the sound signal by 5Hz, and it works well in speech reinforcement, because the frequency range of speech is between 130 and 350Hz, and 5Hz The change of frequency will not make people have a clear sense of pitch increase; while the lower limit frequency of vocal and instrumental music is about 20Hz, and the pitch change of 5Hz has a clear sense of pitch change.

　　b. Equalizer and Feedback Suppressor

　　The reason why howling occurs is because the signal of some frequencies in the system is too strong, and the howling can be suppressed by weakening this part of the signal. Suppress howling. The difference is that the equalizer requires the sound engineer to manually pull the feed point down according to the frequency of the whistle; the feedback suppressor can automatically find the whistling frequency and attenuate it, which hardly affects the music, and also makes the microphone pick up. The voice becomes nice, more suitable for Xiaobai.

　　c. Compressor

　　The limiter can automatically change the output signal amplification (gain) according to the strength of the input signal, so when the volume is so loud that howling is about to occur, the sound signal strength will exceed the threshold through the compressor, so that no whistling will occur. . The fly in the ointment is that the use of a compressor to suppress howling will bring about a loss of sound dynamics.

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