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How professional microphone receives better human voice
It is necessary to eliminate the howling of the feedback from the necessary condition of the feedback whistle, so long as one of the conditions can be destroyed, the purpose can be achieved.
Adjustment distance method
One of the most effective ways to avoid whistling and to increase the volume of sound amplification is to pick up the microphone as close as possible to the sound source, while the microphone should use non directivity. It is clear here that directional microphones (especially the sharp directional microphones) have very small attenuation of the sound source, and the tuning distance is of little effect on the increase of the volume of sound amplification and the prevention of howling. The sound reinforcement system is easy to whistle, no direct relationship with the microphone sensitivity. Only the high sensitivity of the microphone is sharp directivity, prone to howling. The sound equipment shorten the distance with the audience, actually can enhance the loudness of amplifying sound. The total gain of the system can be reduced appropriately. If supplemented by pointing to the near field of wide speakers, microphone slightly away to avoid howling.
For the direct feedback sound field of loudspeakers, the longer the speaker is from the speaker, the better the speaker is from the listener. The microphone should be placed on the back of the speaker's radiation direction. If the microphone is likely to be moved around, the speaker should be placed close to the microphone.
Frequency equalization method (broadband notch filter)
Because the frequency curve of microphone pickup and sound producing equipment is not ideal flat line (especially some poor quality playback equipment), and the acoustic resonance effect of hall sound field, the frequency response fluctuates greatly. You can use the frequency equalizer compensation amplification curve, the linear frequency response of the system to approximate the frequency, the gain is consistent, improve the system transmission gain.
More than 21 segments of equalizer should be used. The parameter equalizer should be configured in higher requirements, and feedback suppressors may be used when higher requirements are required. In fact, when the feedback system is self excited, the frequency of the system is only pure tone fixed at a certain point, so if the frequency notch is removed by a narrow band notch, the system whistle can be suppressed.
Feedback suppressor method (narrowband notch filter)
In demanding situations, such as some live concerts where the widespread use of automatic audio feedback suppression device, the device can automatically track the feedback frequency, automatically adjust the value of bandwidth, automatic acoustic feedback cancellation and maximize the protection of the quality. Its principle is through the notch suppression howling. For example, Sabine FBX series feedback suppressor, it is a kind of microcomputer controlled by the 9 narrowband automatic pressure limit device can distinguish self feedback signal and a music signal, which appears in the system of self, to respond quickly, and set in the feedback frequency on a narrow digital filter, the notch the depth is automatically set, the filter bandwidth is only 1/3 octave band notch is so narrow, almost does not affect the loudness and tone.
Reverse phase cancellation
Phase offset prevent self excitation in high frequency amplification circuit is more common.
In two the same specifications using audio amplification circuit of the microphone are picking up the direct sound and reflected sound, the reflected sound signal into the amplifier before the phase offset by inverting circuit, which can effectively prevent the self-excited howling.
Phase modulation method
The feedback loop of the amplifying system is positive feedback. If the microphone signal is modulated by phase modulation, the self-excited phase condition will be destroyed so as to prevent the self-excited howling of the system. The data show that when the phase deviation is 140 degrees, the stability is the best; and the higher the modulation frequency is, the better the stability of the system is. In order to make the processed sound without distortion is too large, the modulation frequency of the maximum allowed value is 4Hz.
Finally, when all kinds of equipment are adjusted, never let other people tamper with, including some unfamiliar with the performance of the equipment, only open, shut down, adjust the volume of the DJ.
1. Balanced mode to suppress howling
The equalizer (here refers to the graphic equalizer panel with the actual distribution of putting the sound pressure spectrum, intuitive and clear so its name) is 20Hz~20000Hz in the voice band according to certain octave (multiple relation) by paragraph, the most common 15 segment and a 31 segment equalizer (dual channel and single channel regardless). The international conventions, 15 2/3 octave band equalizer according to the relationship between the section select the center frequency, from the low end to high end center frequency at 25Hz, 40Hz, 63Hz, 100Hz, 160Hz, 250Hz, 400Hz, 630Hz, 1KHz, 1.6KHz, 2.5KHz, 4KHz, 6.3KHz, 10KHz and 16KHz were 15 and 31; according to the relationship between the 1/3 octave band equalizer section select the center frequency, from the low end to high end center frequency at 20Hz, 25Hz, 31.5Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz, 125Hz, 160Hz, 200Hz, 250Hz, 400Hz, 500Hz, 315Hz, 630Hz, 800Hz, 1KHz, 1.25KHz, and 1.6KHz 2.5KHz, 3.15KHz, 2KHz, 4KHz, 5KHz, 6.3KHz, 8KHz, 10KHz, 12.5KHz, 1.6KHz, 20KHz, a total of 31. The frequency point of the equalizer is completely fixed, and the push rod set at each frequency point can lift or attenuate the sound pressure at the frequency point by + 15dB (i.e., 6, 7 times volume).
How does equalizer control the noise of the amplifier? We know that the equalizer segments the audio frequency in advance, and the peak of the room where the sound reinforcement whistle is triggered will always fall within a certain frequency band of the equalizer. The correct steps of using equalizer antilarsen is first to the frequency point of the equalizer ring push rod is placed in the center, ensure the equalizer response straight in the audio range; slowly increases the system volume, the system first howl point critical, through subjective judgment howl point frequency; quickly find the charge of the push rod the frequency point in the equalizer, and quickly pulled down the push rod, then the system will reduce the frequency of large discharge, howling disappeared; similarly, continue to increase the system volume, the system second howl point critical, behind the operation in such push...... Until the system is up to volume.
From the above proof process of howling equalizer, has the following characteristics: first, using the manual; two is the number of people are very familiar with the pronunciation of the ear to frequency; three, must act quickly, determine the frequency and the operation should be in place quickly, not to make mistakes, or for a long period of howling may trigger system stability and burning. It is obvious to the operator's requirements, non professional competency.
In fact, there used to suppress howling and equalizer problems are as follows:
The value of the center frequency is low. The Q ＆#118alue is the meaning of a push rod when the drop equalizer such as 1KHZ putter, 1KHz sound volume decreased at the same time, the volume under the influence of 1KHz on the adjacent sound will also affect the size of strength is decreased; with the Q ＆#118alue that the frequency range of influence is smaller the higher the value, the more influence high value is low. Obviously, we will require the equipment to eliminate harmful peaks, while the more the other frequency components retain, the more fidelity the sound is, and the fuller the sound, which means that the device has a high value. Generalized that pull push rod will affect the equalizer and its upper and lower adjacent bands. From the division of the band, when pulling the center frequency of 1KHz push, for the 15 segment equalizer, the impact will be 2/3 octave range on the inside, that is 630Hz~1.6KHz; for the 31 segment equalizer, the impact will be 1/3 octave range in the upper and lower, namely 800Hz~1.25KHz, obviously, the low Q equalizer not only let the sound become full ＆#118alue while reducing the left peak position of large range of useful sound pressure.
Low attenuation. In front of known attenuation equalizer putter in 15dB, only 10~12dB (individual equalizer can be converted to the attenuation between 4~7 times), howling for some serious room, the peak point of the range will be very high, the amount of attenuation needed between 10~20 times, obviously, when the equalizer cannot meet the attenuation peak overcome the point, it is difficult to suppress howling happened. In fact, the value and attenuation is a pair of contradictions in the practice of equalizer, to obtain a large attenuation, value will be further reduced; to obtain high value of equipment, attenuation will be discounted.
Center frequency fixed. The center frequency of the equalizer is set up in advance, and the peak point of different sound live microphone position change is different, the center frequency of the fixed peak resulting not tend to suppress the degradation, when debugging are adjacent two drop-down putt, introduced value we know from in front of two groups of push rod adjacent is pulled down the loudness effect of live sound reinforcement fullness, sound level and wider frequency range of sound in a wider frequency range, but this is partly offset by sound energy.
Obviously, a frequency equalizer and its number for the howling inhibition of its more realistic significance; some professional mixer or simple integrated machine control panel, there will always be 5, 7, 9 single and double band equalizer equalizer, this low digit is used to suppress howling is laughable. In fact, only the equalizer for howling suppression of auxiliary functions, its main function is when the sound or recording program, frequency characteristic curve up and correction effect on the sound pressure field room (equilibrium effect) or complement modification, debugging of program content and performance equipment equipment enduring tone equalizer and a lot of use and necessary reason used in the amplifying system here; and, indeed non professionals are difficult to use good equalizer, use not to, but just the opposite.
Summary: the problems and defects of the equalizer equipment restricts its development in the natural antilarsen fields and use, and with a high price to buy a professional equalizer is used in antilarsen, with its auxiliary function, and its main function is to evade the crucial point, waste The loss outweighs the gain.. With the spread of the follow-up anti whistle technology, equalizer has rarely been used to prevent howling, the use of equalizer to suppress howling is the product of a certain stage.