How to prevent the microphone from howling

Why does the microphone produce feedback whistle?

After the microphone is picked up, the sound is amplified by the mixer, peripheral equipment, power amplifier, and speaker. This sound enters the microphone through direct radiation or acoustic reflection, causing the entire sound reinforcement system to generate positive feedback, causing the acoustic and electrical signals to self Encourage, the loudspeaker then whistle sound, this kind of phenomenon is called the sound feedback of the microphone.

What harm will the microphone squeal cause?

(1) It destroys the atmosphere of the entire sound reinforcement environment, makes the speaker or singer very embarrassed, makes the audience very disappointed, and even produces disgust.

(2) It has a great impact on the power amplifier or the tweeter unit of the speaker, and it is easy to overload them and burn them.

(3) Due to the existence of acoustic feedback, the sound transmission gain and sound power of the entire sound reinforcement system are limited (that is, the volume cannot be increased).

How to avoid microphone whistling?

(1) Avoid placing the microphone in the radiation area of the speaker (at least not directly facing the speaker). First, adjust the level of a microphone, without adding the microphone equalization of the mixer, and place the mixer channel fader at the 0 decibel position (if the signal for the stage monitoring is taken from the auxiliary output after the fader, do so) . Place the microphone on the main position on the stage, turn on the monitor output control (AUX) and gradually increase the output. After the microphone causes howling in a certain frequency band, fine-tune the AUX knob to stabilize the howling at a certain volume level, and then adjust the corresponding balance To eliminate the howling in this frequency band, and then continue to increase the volume. After the howling in another frequency band is generated, adjust the equalizer to eliminate it, and so on. Normal position (such as 0dB), the microphone no longer produces howling, OK, pull down the mixer fader. This method is used to find out the howling points in the sound field that are likely to cause resonance, and then appropriately reduce the level of the microphone channel, find someone to talk to the microphone on stage, and then gradually increase the microphone volume to the normal position. If there is still howling, then Eliminate by equalizer. Operating points: Be sure to control the level so that it can be maintained at a stable level after the howling occurs, and then it is more accurate to adjust. The operation must be slow, otherwise, once you scream, you won’t be able to find the correct squeal point one by one. The resonance point in the room is generally around 5-6 points. If there are too many feedback points, you need to check whether the speaker placement is reasonable. After adjusting the howling point of the monitor, adjust the main sound reinforcement system in the same way. If the main sound reinforcement is a two-channel system, turn off one channel first, push the input fader of the mixer, and gradually increase the volume to find Howling point. After adjusting one channel, turn off this channel and adjust the other. After adjusting both sides, push the two channels up at the same time to check if there are other howling points, and then eliminate them through the equalizer.

(2) Choose a suitable microphone according to the actual situation, use a relatively high-quality microphone as a reference (SHURE BETA87A is recommended), adjust the balance of the microphone input channel, and use the microphone tone as close as possible to the high-quality microphone used for reference. After completing this step, the microphone tone can generally meet the requirements of most people, and then let the user test the microphone and make appropriate fine-tuning of the mixer channel balance according to the user's requirements.

(3) Do a good job in the architectural acoustic design of the room to fully consider the uniform absorption (reflection) of each frequency by the sound-absorbing materials and sound-absorbing structure, so as to reduce the reflection or inconsistent absorption of the sound of different frequencies, especially in the space near the microphone. , The acoustic reflection should be reduced as much as possible.

(4) The equipment is connected firmly to avoid the phenomenon of false welding (false welding or weak connection can cause instantaneous resistance increase and attenuation, and voltage instability).

(5) Debug the equipment for overall adjustment. Each type of equipment cannot be in a critical working state, otherwise the signal will be unstable or oscillate.

(6) Feedback suppressor or frequency shifter can be added to suppress and eliminate howling. After adjusting the original tone of the microphone, you can add reverberation, use the effector to select the appropriate effect type, turn on the corresponding AUX output of the mixer, and adjust the input level of the effector and the auxiliary output level of the mixer at the same time, and speak to the microphone , To see if the signal output to the effector is too large or too small, generally control this signal at 0 decibels. Set the effector mixing ratio to 100%, and then gradually increase the output level of the effector to check whether the level of the output callback console is normal. If it is normal, gradually increase the return knob of the effector. According to the user’s requirements, Set the amount of effector to an appropriate level. After the effect is added, due to the existence of artificial reverberation, a new howling point may be generated. Generally, the first howling point is easy to appear in the low frequency band. The microphone manufacturer recommends that the effector return is connected to the line input of the mixer. Then you can adjust the balance of this input channel to eliminate howling.

The selection, debugging, installation, placement, etc. of audio equipment are very important to solve the problem of howling. However, solving the quality of the tuner, solving the error of equipment matching, and curbing the use of inferior equipment are also necessary to effectively solve the problem of howling. Indispensable.