What if the microphone screams? Five Methods for Eliminating Microphone Feedback Whispering

Release time:

2021-06-24

Sound systems that pick up sound from microphones may have feedback squealing. The harm of microphone squealing is significant, mainly manifested in the following aspects:
1. When self-excited, the power amplifier will produce a large power output, which may exceed the withstand range of the sound reinforcement equipment, and burn out the power amplifier and sound generating equipment.
2. When the feedback coefficient is close to 1, due to the comb filtering effect, the superposition between the delayed sound field and the direct sound field will make the amplified sound field narrower in sound sense than the original sound field.
3. The delayed feedback of the speaker sound field will cause a series of delayed echoes to form throughout the system, and this echo will accentuate the comb filtering effect, resulting in significantly distorted reverberation, trailing, and reverberation distortion.
4. The output sound pressure during whistling is very high, which seriously affects the atmosphere of various activities.
Eliminating feedback squealing requires starting with the necessary conditions for generating feedback squealing. As long as one of these conditions can be broken, the goal can be achieved. The following are the top 5 methods for eliminating microphone feedback squealing recommended by CCTV.
1. Eliminating microphone feedback squealing using inverse cancellation
Anti phase cancellation to prevent self excitation is common in high-frequency amplification circuits. Two microphones of the same specification can be used in the audio amplification circuit to respectively pick up direct sound and reflected sound. The inverted circuit can cancel out the phase of the reflected sound signal before entering the power amplifier, effectively preventing howling self-excitation.
2. Eliminating microphone feedback squealing by adjusting distance
One of the most effective ways to avoid whistling and increase the sound amplification volume is to place the microphone as close to the sound source as possible, and use a non directional microphone. To be clear, directional microphones (especially sharp directional microphones) have very small pickup attenuation from distant sound sources, and adjusting the distance has little effect on improving the sound amplification volume and preventing whistling. Whether a sound reinforcement system is prone to howling is not directly related to the sensitivity of the microphone. It's just that highly sensitive microphones are highly directional and prone to squealing. Reducing the distance between the sound producing device and the audience can actually improve the loudness of the sound reinforcement. The total gain of the system can be appropriately reduced. If accompanied by a near field speaker with wide directivity, the microphone can be avoided by being slightly distant.
For the direct feedback sound field of speakers, the farther the microphone is from the speaker, the better. The closer the speaker is to the audience, the better. The microphone should be placed on the back of the radiation direction of the speaker. If the microphone is likely to be carried around, the speaker should be placed where the microphone cannot be brought very close.
3. Eliminating microphone feedback squealing using phase modulation
The feedback loop of self-excited whistling in a public address system is positive feedback. If the microphone signal is phase modulated, the phase condition of self-excited whistling will be destroyed, thereby preventing self-excited whistling in the system. Some data indicate that when the phase deviation value is 140 °, the stability is the best; Moreover, the higher the modulation frequency, the better the stability of the system. In order to avoid too much distortion in the processed sound quality, the maximum allowable value of its phase modulation frequency is 4 Hz.
Finally, after adjusting various devices, never let others move around, including DJs who are unfamiliar with the performance of the device and only know how to turn it on, off, and adjust the volume.
4. Feedback suppressor method (narrowband notch method) to eliminate microphone feedback squealing
In highly demanding situations, such as some live singing places, audio frequency feedback automatic suppression devices are commonly used. This device can automatically track the frequency of feedback points, automatically adjust the Q value bandwidth, automatically eliminate acoustic feedback, and maximize the protection of sound quality. The principle is to suppress whistling by trapping waves.

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