The reason why the microphone produces howling
The sound system of the microphone pickup has the possibility of feedback howling. The risk of microphone whistling is very high, mainly in the following aspects:
1. The power amplifier will generate a large power output during self-excitation, which may exceed the bearing range of the sound reinforcement equipment and burn out the power. Amplifiers and sound-generating equipment.
2. When the feedback coefficient is close to 1, due to the comb filter effect, the superposition between the delayed sound field and the direct sound will make the amplified sound field narrower in sound than the original sound field.
3. The delay feedback of the speaker sound field will make the whole system form a continuous series of delay responses, and this type of response will aggravate the comb filter effect, resulting in a significantly distorted reverberation tail—— Just rang true.
4. The sound pressure output during whistling is very large, which seriously affects the atmosphere of various activities.
Elimination of feedback whistling should start with the premise of generating feedback whistling. As long as one of the preconditions can be broken, the goal can be achieved.
How to clear the howling of the microphone
1. Adjustment interval method
Both to avoid howling and to One of the most effective ways to increase the volume of the amplification is to place the microphone as close to the sound source as possible, and the microphone should be non-directional. It is clear here that the pickup of directional microphones (especially sharp-directional microphones) far away from the sound source has little attenuation, and the adjustment interval has little effect on increasing the amplification volume and avoiding howling. Whether the sound reinforcement system is easy to whistle has nothing to do with the flexibility of the microphone. Only the microphones that are not too active are sharp directivity, which is easy to produce howling. Shortening the distance between the sounding equipment and the audience can actually increase the loudness of the amplification. The overall gain of the system can be appropriately reduced. If supplemented by near-field speakers with wide directivity at the same time, the microphone can be slightly farther away to avoid howling.
For the direct feedback sound field of the speaker, the farther the microphone is from the speaker, the better, and the closer the speaker is to the listener, the better. The microphone should be placed on the back of the target of the speaker radiation. If the microphone is likely to be carried around, the speaker should be placed in a place where the microphone cannot get close.
2. Frequency equalization method (broadband notch method)
Because the frequency curve of the microphone pickup and sound-emitting device is not an ideally flat straight line (especially Some poor-quality playback equipment), and the acoustic resonance of the hall sound field, so that the frequency response fluctuates greatly. The frequency equalizer can be used to compensate the sound reinforcement curve, and the frequency response of the system can be adjusted to an approximate straight line, so that the gain of each frequency band is basically the same, and the sound transmission gain of the system can be improved.
Equalizers with more than 21 bands should be used, and parametric equalizers should be built in places with higher requirements. When the requirements are higher, feedback suppressors can be used. In fact, when the sound reinforcement system exhibits feedback self-excitation, its frequency is only a pure tone fixed at a certain point. Therefore, as long as a notch filter with a narrow frequency band is used to cut this frequency, the howling of the system can be suppressed.
3. Feedback suppressor method (narrow-band notch method)
The reason is to suppress howling through the notch. For example, Sabine’s FBX series feedback controller is a 9-segment narrow-band active voltage limiting device controlled by a microcomputer, which can better distinguish feedback self-excited signals and music signals. Respond quickly, and set a very narrow digital filter at the feedback frequency point, and its notch depth will also be automatically set, and the filter bandwidth is only 1/3 octave, such a narrow notch frequency band, almost No effect on loudness or timbre.
