Usually at the event site, if the field staff does not handle it properly, the microphone will make a harsh sound when it is close to the speaker. This harsh sound is called “ howling †or “ feedback gain †. This process is due to the microphone input signal being too large, causing the sound of the released sound to cause howling.
Acoustic feedback is not a normal phenomenon sound system (PA) that often appear, he is sound reinforcement system unique acoustic problems, for sound reproduction, it turns out to be a hundred more harm than good. People who are engaged in professional audio, especially those who are professional in the field of sound reinforcement, are really abhorrent to the speaker whistling, because the troubles caused by the whistling are innumerable, and the majority of professional audio workers have almost racked their brains to eliminate it. However, it is still impossible to completely eliminate the whistle. Acoustic feedback howling is a howling phenomenon caused by the sound energy transmitted to the microphone through the way of sound propagation. In the critical state where there is no howling, a ringing tone will occur. At this time, it is generally considered that there is a howling phenomenon. After attenuation of 6dB , it is defined as no howling occurs.
When using the microphone to pick up the sound in the sound reinforcement system, since the sound pickup area of ​​the microphone and the sound emitting area of ​​the sound box cannot be acoustically isolated, the sound emitted by the sound box can easily be transmitted to the microphone through the space and cause howling. In general, there is a howling problem only in the sound reinforcement system, and there is no condition for generating a howling in the recording and restoration system. For example, if there is only a monitor speaker in the recording system, the use area of ​​the flower tube in the recording studio is isolated from the sound playback area of ​​the monitor speaker, and there is no condition for sound feedback; in the movie sound system, almost no microphone is used, even if it is encountered With the microphone, the voice is also heard in the projection room, and the speaker is far away from the microphone, so it is impossible to whistle.
Reasons for howling may occur:
1. Simultaneous use of microphone and speaker;
2 , the sound of the audio delivery can be transmitted to the microphone through the space;
3. The sound energy emitted by the speaker is large enough, and the pickup sensitivity of the microphone is high enough.
Once the howling phenomenon occurs, the volume of the microphone channel cannot be adjusted greatly. After the adjustment, the howling is very serious, which will have a very bad effect on the live performance, or the sound ringing will occur after the microphone sounds louder. When the whistle is called the critical point, the sound of the microphone sounds. The sound has a sense of reverberation and destroys the sound quality. If the speaker or power amplifier is burnt due to excessive signal, the performance cannot be performed normally, resulting in huge economic loss and reputation loss. Judging from the level of sound accidents, all silent and howling is the biggest accident, so the speaker should enter the maximum possibility to avoid the occurrence of howling, so as to ensure the normal operation of the sound reinforcement.
A method that can effectively avoid howling:
Keep the microphone away from the speaker;
Reduce the volume of the microphone channel;
Use the pointing characteristics of the speaker and microphone to avoid the respective pointing areas;
Using a frequency shifter;
Using an equalizer and feedback suppressor;
Reasonable selection of speakers and microphones.
It is the responsibility of the sound workers to talk to the speaker and the unremitting struggle. With the continuous development of sound technology, there will be more and more means to eliminate and suppress howling, but in theory, the sound reinforcement system will eliminate the noise. The phenomenon of calling is also not very realistic, so it is only necessary to take necessary measures to avoid the occurrence of howling in the normal system use.
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