What Is a Feedback Eliminator?

Feedback Exterminator In the sound reinforcement system, if the microphone volume is greatly increased, the sound from the speaker will be transmitted to the howling caused by the microphone. This phenomenon is acoustic feedback. The existence of acoustic feedback not only destroys the sound quality, limits the extended volume of the microphone sound, and makes the sound picked up by the microphone not well reproduced; the deep acoustic feedback will also make the system signal too strong, which will burn the amplifier or speaker (generally, burned Tweeter), causing damage. Therefore, once an acoustic feedback phenomenon occurs in a sound reinforcement system, we must do everything we can to stop it, otherwise it will endless harm. ^[1]

A feedback suppressor is a device that automatically pulls feed points.

In the sound reinforcement system, if the sound output power is increased or the microphone volume is greatly increased, the sound from the speaker enters the microphone directly or indirectly, so that the entire sound reinforcement system forms positive feedback, resulting in certain frequency points. If the sound is too strong to cause howling, this phenomenon is called acoustic feedback, also called sound return.

There are many reasons for acoustic feedback. The main reason is that the design of the indoor sound reinforcement environment is unreasonable, followed by the unreasonable speaker layout, and then the poor debugging of the audio equipment and system. Specifically includes the following four aspects:

(1) The microphone is directly placed in the speaker radiation area, and its axial direction is directly aligned with the speaker.

(2) The sound reflection phenomenon in the sound reinforcement environment is serious, and the surroundings and ceiling are not decorated with sound-absorbing materials.

(3) Improper matching between audio equipment, serious signal reflection, false soldering on the connection line, and sound signal on and off when the contact point flows.

(4) Some equipment in the audio equipment is in a critical working state. When the sound signal is large, an oscillation phenomenon occurs.

Acoustic feedback is the most headache in the sound reinforcement of the hall. Whether it is in the theater, the venue or the dance hall, once the acoustic feedback will not only destroy the normal working state of the entire sound system, damage the sound quality, but also destroy the conference Performance effect. Therefore, the suppression of acoustic feedback is an extremely important issue that must be paid attention to in the process of debugging and application of sound reinforcement systems. Sound workers should understand acoustic feedback and find better methods in time to avoid or minimize howling caused by acoustic feedback. .

The howling of the audio system is caused by the positive feedback that constantly strengthens certain frequency points in the audio signal. If these frequency points are cut off or greatly attenuated, the acoustic feedback can be effectively suppressed. The feedback suppressor is designed based on this idea, and its working principle is: use computer technology to quickly scan, automatically find out howling audio signal frequencies (howling frequencies), and automatically generate a set of these howling frequencies The same narrowband filter is used to cut off the howling frequency, so as to achieve the purpose of automatically suppressing howling and eliminating acoustic feedback.

The feedback suppressor consists of an amplifier, an A / D converter, a narrowband digital filter bank,

Whether or not acoustic feedback can be eliminated is an important indicator to measure the technical level of an acoustic engineer. Before the appearance of a feedback suppressor, the acoustic engineer often used an equalizer to pull the feed point (attenuating the feedback frequency) to suppress acoustic feedback. The reason that sound reinforcement systems produce acoustic feedback is mainly because the sound at certain frequencies is too strong. Attenuating these excessively strong frequencies can solve this problem, but using the equalizer to pull down can produce the following insurmountable disadvantages:

The first is that the sound level of the sound engineer is extremely high. After the feedback, the sound engineer must judge the feedback frequency and degree in a timely and accurate manner, and immediately and accurately attenuate this frequency of the equalizer. It is difficult for a rich sound engineer.

The second is to have a certain impact on playback sound quality. The band width of the existing 31-band equalizer is 1/3 octave, and the bandwidth of some acoustic feedback that needs to be attenuated is sometimes much smaller than 1/3 octave. At this time, many useful frequency components will be removed. These frequencies can cause irreparable losses.

Third, equipment may be burned during the adjustment process. It takes a certain time to judge howling frequency with human ears. If this time is too long, the equipment should cope with damage due to being in a strong signal state for a long time. The use of a feedback suppressor can completely solve this problem, which can effectively eliminate feedback without affecting the playback sound quality, so its superiority is obvious.