Most sound engineers have this experience: when using a single microphone, if the microphone howling occurs, the use of an acoustic feedback suppressor (such as the insertion method) can ideally suppress the howling noise; however, when at the same time When using multiple microphones, the howling effect received is often not ideal, and often only some of them or even a single microphone have better suppression effects. When the other microphones push the volume up, the howling sound does not Get suppressed. So, where does the problem lie? Let's talk about the causes and solutions to this problem.
As everyone knows, due to the structure and characteristics of microphones, the frequency response, impedance, sensitivity, directivity and other indicators of microphones of different brands are inconsistent. Even microphones of the same brand have different degrees of difference in these indicators, plus Objective factors such as different uses and placement positions of the above microphones in actual use cause the feedback howling frequency of each microphone does not occur at the same volume.
If we use the conventional method for frequency shifting, the microphone with the first howling will trigger the suppressor to perform point-by-point frequency shifting. As a result, the remaining microphones with no howling have not been effectively shifted. When the volume is turned up, these microphones will still howling, and the suppressor is helpless. If we use multiple acoustic feedback suppressors to interpolate the frequency of each microphone separately using the insertion method, then these many problems can be solved, but this leads to an increase in equipment costs. If a comprehensive singing and dancing party is held, this configuration will cost labor and time to install and debug, and second, it will be very impractical in terms of cost. In fact, the solution is very simple, as long as we use the correct debugging method, a feedback suppressor can completely obtain the ideal frequency shift suppression effect.
Let's take a practical example in the performance and introduce the operation method of the debugging in detail.
For example, there is a skit program in the performance, and 8 lavalier microphones are needed at the same time.
1. Program 8 lavalier microphones as a group on the mixer, adjust the EQ of each channel of high, middle and low tones and the GAIN button of each channel of gain to the midrange position, and then push the auxiliary volume of each channel The child pulled down.
2. On the stage, concentrate these 8 microphones at the place where whistling is most likely to occur, and then place them on a platform about 1m above the stage floor.
3. Connect the sound reinforcement system as usual. Use the insertion method to insert the feedback suppressor into the group INSERT interface corresponding to these 8 microphones.
4. Set all peripheral equipment (including the acoustic feedback suppressor) connected in series between the mixer and the power amplifier on the bypass, and set the input and output knobs of each equipment at 0dB, and set the power amplifier attenuation button. In the middle position.
5. Set the microphone group output fader and the main output fader on the mixer to 0dB. Through the cooperation between the gain button and the auxiliary fader, debug each channel microphone separately.
6. Slowly push up the auxiliary volume fader of one of the microphones until the stable howling sound appears. Remember the decibel position on the fader, and then pull the fader down, and then debug the second microphone, and so on, until these 8 microphones all debug a stable howling. This step is very important and requires patience and fine-tuning.
7. Pull down the main output fader on the mixer to restore the position of the sub-faders of each tube to the appearance of howling.
8. Restore the bypass key of the acoustic feedback suppressor to the working state, and select the S1 single-point filtering method, and then slowly pull up the main output fader. After the sound appears, the suppressor will suppress the howling of these 8 microphones frequency by frequency until the red filter indicator lights on the suppressor no longer flash.
9. Finally, press the STORE key, use the rotary wheel to select the storage number, and then press the STORE key to store the adjustment results.
10. After restoring each peripheral equipment to the working state, the entire commissioning work will be completed.
Through the debugging of the above ten steps, these 8 lavalier microphones can all work steadily in the best condition, thus effectively suppressing the acoustic feedback that is easy to appear in the performance.
The picture shows the MARK K800 feedback suppressor
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