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Acoustic Feedback - Cause of acoustic feedback and preventing measures-

An acoustic feedback, an undesirable prolonged howling sound will be produced in a loudspeaker when it is located close to a microphone.

Acoustic feedback mechanism

When a microphone is located near a loudspeaker within a limited or enclosed space such as hall or auditorium, portion of sound from the loudspeaker can be picked up by the microphone. The sound is reamplified and the higher acoustic power is output through the speaker. Repetition of this process through the feedback loop causes the speaker to produce annoying screeching or low-frequency booming noises.


[1] The sound picked up by the microphone is fed back at a high enough level, in phase, to the amplifier.
[2] The boosted sound is radiated into air through the loudspeaker.
[3] Portion of the sound from the speaker is picked up by the microphone and fed to the amplifier as described in [1]

acoustic feedback mechanism

Frequency response of acoustic feedback loop

Each space has unique acoustic characteristics depending on its conditions such as its dimensions and geometry, materials of ceiling and wall, and location and orientation of loudspeaker and microphone.
This characteristics curve, called the frequency response curve can be graphically expressed as shown below.
The frequency response curve contains peaks and troughs. A sound component at a peak frequency tends to produce a howling. As the sound picked up by the microphone is amplified, the energy of sound components at peak frequency is sharply increased, causing the speaker to howl. When the frequency of feedback is high, it is called “screeching” and “booming” when low.

Frequency response

Cause of trouble

Acoustic feedback is offensive sound to ear of many people. It can destroy events such as speech, lecture and concert.
Feedback associated with excessive acoustical vibration and electrical energy will cause damage to the loudspeaker and amplifier.

How to decrease possibility of feedback

Right selection, layout, arrangement and setup of system components will decrease or eliminate possibility of feedback.
The gain of the amplifier at a particular frequency where feedback will take place can be turned down by using a graphic equalizer.
Feedback Suppressor (FBS) will prevent any feedback including accidental ones.