Why does the microphone produce a back-losing howl?
After the microphone picks up the sound, through the mixer, peripheral equipment, power amplifier, speaker to expand the sound, this sound through direct radiation or sound reflection way into the microphone, so that the entire sound amplification system produces positive feedback, causing the acoustic signal self-motivation, the speaker then whistling, this phenomenon is called the microphone's sound feedback.
What are the harms of microphone whistling?
(1) Destroyed the atmosphere of the whole sound-amplification environment, so that the speaker or singer is very upset, so that the audience is very upset, and even produce disgust.
(2) The high-pitched speaker unit of the power amplifier or speaker has a great influence, and it is easy to overload them and burn them.
(3) Due to the presence of acoustic feedback, the transmission gain and sound power of the entire sound amplification system are limited (i.e. the volume cannot be increased).
How do I avoid microphone whistling?
(1) Avoid placing the microphone in the radiation zone of the speaker (at least not lying on the horn). First set the level of a microphone, first without the mixer microphone equalization, the mixer channel pusher placed in the 0 dB position (if the signal to the stage monitor is taken from the pusher after the auxiliary output to do so). The microphone is placed in the main position on the stage, the listening output master (AUX) is turned on and the output is gradually pushed up, and so the microphone causes a certain band to howl, fine-tune the AUX knob to stabilize the whistling at a certain volume level, and then adjust the corresponding equalizer to make this band howl Eliminate, and then continue to increase the volume, and so on another band of howling produced, and then by adjusting the equalizer elimination, and so on, such as the mixer output level pusher or AUX knob adjusted to the normal position (such as 0dB), the microphone no longer produces whistling, OK, pull down the speaker pusher. This method is used to find out the sound field easy to cause resonance of the whistling point, and then appropriately lower the level of the microphone channel, find a person on stage to speak to the microphone, and then gradually increase the microphone volume to the normal position, if there is a whistling, and then through the equalizer elimination. Key points of operation: be sure to control the level, so that the whistling can be maintained at a stable level and then adjust more accurately. The operation must be slow, otherwise as soon as you call up, you can't find the right whistling point one by one. Resonance points in the room are usually around 5-6 points, if there are too many feedback points, you need to check whether the speaker position is reasonable. After tuning the listening whistling point, and then adjust the main loudspeaker system in the same way, if the main amplifier is a two-channel system, first close a channel, push the input fader of the mixer, gradually increase the volume to find the whistling point. After tuning one channel, turn off the channel to tune the other, both sides are tuned, and then push the two channels up at the same time to check whether there are other whistling points, and then through the equalizer to eliminate.
(2) According to the actual situation to choose the right microphone, with a relatively high quality microphone as a reference, (recommended to use SHURE BETA87A), adjust the microphone input channel balance, the use of microphone tone as close as possible to the high-quality microphone used for reference, after this step, the microphone tone can generally meet the requirements of most people, and then let the user dialogue tube test sound, according to the user's requirements, the mixer channel balance to do the appropriate fine-tuning can be.
(3) Do a good job of room building acoustic design fully consider the sound absorption material and sound absorption structure of each frequency absorption (reflection) uniform problem, in order to reduce the different frequencies of sound reflection or absorption in inconsistent situations, especially in the space near the placement of the sound transmitter, should minimize acoustic reflection.
(4) the connection between the equipment is secure, to avoid the phenomenon of false welding (virtual welding or weak connection can lead to instantaneous resistance increase and attenuation, voltage instability).
(5) Debugging equipment must be unified, each device can not be in a critical working state, otherwise there will be signal instability or oscillation phenomenon.
(6) A feedback suppressor or shifter can be added to suppress the elimination of howling. After the microphone original tone adjustment, you can add reverb, with the effector to select the appropriate effect type, open the corresponding AUX output of the mixer, while adjusting the effector input level and mixer auxiliary output level, the microphone to speak, to see if the output to the effector signal is too large or too small, generally control this signal at 0 dB. The effector mixing ratio is set to 100%, and then gradually open the output level of the large effector, to detect whether the level of the output callback mixer is normal, if normal, gradually increase the knob returned by the effector, according to the user's requirements, the amount of the effector set to a suitable level. After the effect, due to the presence of artificial reverb, may produce a new whistling point, generally easy to appear in the low frequency band the first whistling point, the best effector return is connected to the mixer line input, then you can adjust the balance of this input channel to eliminate whistling.
Audio equipment in the selection, commissioning, installation, placement and so on to solve the whistling problem is very important, but to solve the tuner's own quality, to solve the equipment mixing errors, to curb the use of inferior equipment, but also to effectively solve the whistling problem is essential.
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