Usually at the event site, if the on-site 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 excessive microphone input signal, which distorts the emitted sound and causes howling.

Acoustic feedback is an abnormal phenomenon that often occurs in sound reinforcement systems (P.A.). It is a unique acoustic problem of sound reinforcement systems. It can be said to be harmful to sound reproduction. People who are engaged in professional audio, especially those who specialize in on-site sound reinforcement, really hate speaker howling, because the trouble caused by howling is endless. The majority of professional audio workers have almost racked their brains in order to eliminate it. However, it is still impossible to completely eliminate the howling. Acoustic feedback howling is a howling phenomenon caused by a part of the sound energy being transmitted to the microphone through sound transmission. In the critical state where there is no howling, a ringing tone will appear. At this time, it is generally considered that there is a howling phenomenon. After attenuation of 6dB, it is defined as no howling phenomenon occurs.

When a microphone is used to pick up sound in a sound reinforcement system, Because it is impossible to take sound isolation measures between the pickup area of the microphone and the playback area of the speaker. The sound from the speaker can easily pass through the space to the microphone and cause howling. Generally speaking, only the sound reinforcement system has the problem of howling, and there is no condition for howling at all in the recording and restoration system. For example, there are only monitor speakers in the recording system, the use area of the microphone in the recording studio and the playback area of the monitor speakers are isolated from each other, and there is no condition for sound feedback. In the film sound reproduction system, microphones are almost not used, even if When using a microphone, it is also used for close-up voice pickup in the projection room. The projection speaker is far away from the microphone, so there is no possibility of howling.

Possible reasons for howling:

1. Use the microphone and speakers at the same time;

2. The sound from the speaker 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 cannot be adjusted very much. The howling will be very serious after it is turned up, which will cause extremely bad effects on the live performance, or the sound ringing phenomenon occurs after the microphone is turned on loudly (that is, when the microphone is turned on The tail phenomenon of the microphone sound at the critical point of howling), the sound has a sense of reverberation, which destroys the sound quality; In severe cases, the speaker or power amplifier will be burnt due to excessive signal, making the performance unable to proceed normally, causing huge economic loss and reputation loss. From the perspective of audio accident level, silence and howling are the biggest accidents, so the speaker engineer should take the greatest possibility to avoid the howling phenomenon to ensure the normal progress of the on-site sound reinforcement.

Ways to effectively avoid howling:

Keep the microphone away from the speakers;

Reduce the volume of the microphone ;

Use the pointing characteristics of speakers and microphones to avoid their respective pointing areas;

Use frequency shifter;

Use equalizer and feedback suppressor;

Use speakers and microphones reasonably.

It is the responsibility of sound workers to fight unremittingly with speaker howling. With the continuous development of sound technology, there will be more and more methods to eliminate and suppress howling. However, theoretically speaking, It is not very realistic for the sound reinforcement system to eliminate the howling phenomenon at all, , so we can only take necessary measures to avoid the howling in normal system use.