Microphone anti-howling method

Why does the microphone produce a whistle?

After the microphone is picked up, the sound is amplified by the mixer, peripheral devices, power amplifiers, and speakers. This sound enters the microphone through direct radiation or acoustic reflection, causing the entire sound reinforcement system to generate positive feedback, causing the acoustic signal self. The excitation, the speaker immediately whistling, this phenomenon is called the sound feedback of the microphone.

What harm does the microphone whistle?

(1) Destroying the atmosphere of the entire sound-enhancing environment, making the speaker or singer very embarrassed, making the audience very disappointing and even averse.
(2) It has a great influence on the tweeter unit of the power amplifier or the speaker, and it is easy to overload and burn them.
(3) Due to the existence of acoustic feedback, the sound transmission gain and sound emission power of the entire sound reinforcement system are limited (that is, the volume cannot be increased).

How to avoid the microphone whistling?

(1) Avoid placing the microphone in the radiation area of ​​the speaker (at least not facing the speaker). First adjust the level of a microphone, first without the mixer's microphone equalization, the mixer channel fader is placed at 0 dB (if the signal for the stage monitor is taken from the fader, the auxiliary output will do so) . Put the microphone on the main position on the stage, turn on the monitor output master control (AUX) and gradually push up the output. After the microphone causes a certain frequency band howling, fine-tune the AUX knob to stabilize the howling at a certain volume level, and then adjust the corresponding equalization. To eliminate the howling in this band, continue to increase the volume, wait for the other party's howling to be generated, then adjust the equalizer to eliminate it, and so on, adjust the mixer output level fader or AUX knob to In the normal position (such as 0dB), the microphone no longer produces howling, OK, pull down the mixer fader. This method is used to find the howling point in the sound field that easily causes resonance, and then appropriately lower the level of the microphone channel, find a person to speak on the microphone, and then gradually increase the volume of the microphone to the normal position, if there is a howling, then Eliminated by the equalizer. Operation points: It is necessary to control the level so that the whistle can be maintained at a stable level and then adjusted. The operation must be slow, or if you call it, there is no way to find the correct howling point one by one. The resonance point in the room is usually around 5-6 points. If there are too many feedback points, it is necessary to check whether the speaker position is reasonable. After adjusting the whistle of the monitor, adjust the main sound reinforcement system in the same way. If the main sound reinforcement is a two-channel system, first close a channel, push the input fader of the mixer, and gradually increase the volume to find Howling. After adjusting one channel, turn off the channel and adjust the other. After both sides are adjusted, push the two channels at the same time and check if there are other howling points, and then eliminate them by the equalizer.
(2) Select the appropriate microphone according to the actual situation, use a high-quality microphone as a reference, (Recommended SHURE BETA87A), adjust the balance of the microphone input channel, use the microphone sound as close as possible to the high-quality microphone used for reference. After this step, the microphone sound can generally meet the requirements of most people, and then let the user audition the microphone, according to the user's request, the appropriate fine-tuning of the mixer channel equalization.
(3) Do a good job in the acoustic design of the room building. Fully consider the problem of uniform absorption (reflection) of the sound absorption material and sound absorption structure to reduce the inconsistency of sound reflection or absorption at different frequencies, especially in the space near the microphone. Sound reflection should be minimized.
(4) The connection between the devices is reliable, avoiding the phenomenon of soldering (the solder joint or the weak connection may cause the transient resistance to increase and decay, and the voltage is unstable).

(5) The debugging equipment must be adjusted. Each device cannot be in a critical working state. Otherwise, the signal may be unstable or oscillating.
(6) A feedback suppressor or a frequency shifter can be added to suppress the cancellation of howling. After the original tone of the microphone is adjusted, you can add the reverb, use the effect 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 to speak to the microphone. To see if the signal output to the effect is too large or too small, this signal is generally controlled at 0 dB. Set the effect mixing ratio to 100%, then gradually turn on the output level of the effect, and check if the level of the output echo stage is normal. If it is normal, gradually increase the knob returned by the effect, according to the user's request. Set the amount of the effect to the appropriate level. After the effect is added, due to the existence of artificial reverberation, a new howling point may be generated, and it is generally easy to have the first howling point in the low frequency band. Preferably, the effect return is the line input to the mixing console. The balance of this input channel can be adjusted to eliminate howling.
The selection, debugging, installation, placement, etc. of the audio equipment are very important for solving the whistle problem, but solving the tuner's own quality, solving the mismatch of the equipment, and curbing the use of inferior equipment are also effective in solving the whistling problem. Indispensable.