How to prevent sound system whistling

　　Howling of the audio system refers to the positive feedback of sound between the pickup and the speaker. This positive feedback goes through an infinite loop, thus forming the phenomenon of self-excitation and feedback. The pickup distance of the microphone is inseparably related to the on-site acoustic environment and the isolation between the microphone and the speaker. Combined, we call the "sound transmission gain" of the system. Under reasonable system configuration, equipment placement and acoustic environment conditions, the sound transmission gain will be improved.

　　Reasons for audio whistling: overloaded level output, too many environmental reflections, too close the distance between the microphone and the speaker, relative pointing angles, uneven frequency response curve of the device, etc.

　　Hazards from whistling:

　　1. Damage the power amplifier and other electro-acoustic equipment.

　　2. Affect the sound reinforcement quality.

　　3. Destroy the atmosphere of the event site.

　　To put it simply, the conditions for howling to occur must meet the following three points:

　　1. Use both the microphone and the speaker at the same time.

　　2. The sound reproduced by the audio system 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.

　　Solution:

　　Eliminating feedback whistling starts with the necessary conditions for generating feedback whistling. As long as one of the conditions can be destroyed, the goal can be achieved.

　　1. Adjust the distance method

　　One of the most effective ways to avoid howling and increase the volume of the amplification is to place the microphone as close to the sound source as possible.

　　2. Shortening the distance between the sounding equipment and the audience can actually increase the loudness of the sound reinforcement.

　　3. The farther the microphone is from the speaker, the better. The microphone should be placed on the back of the speaker's radiation direction, or not in the front of the speaker.

　　4. Broadband notch method, since the frequency curve of the microphone pickup and sound-generating equipment is not an ideal flat straight line, the frequency response of the system can be adjusted to an approximate straight line through the EQ of the audio processor, so that the gain of each frequency band is basically the same, which can be Relatively improve the sound transmission gain of the system.

　　5. The feedback suppressor method, also known as the narrow-band notch method, uses an automatic audio feedback suppression device, which can automatically track the frequency of the feedback point, automatically adjust the Q value bandwidth, and automatically eliminate the acoustic feedback while maximizing the protection of the sound quality. . The principle is to suppress howling through a narrow notch, while maximizing the protection of the sound from being affected.

　　6. Inverse cancellation method to prevent self-excitation is common in high-frequency amplifier circuits.

　　In the audio amplifier circuit, two microphones of the same specification can be used to pick up the direct sound and the reflected sound respectively, and the reflected sound signal can be canceled out of phase before entering the power amplifier through the inverting circuit, which can effectively prevent the self-excitation of howling.

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