Posted by : Paras Sharma Thursday, 10 December 2015

We all have heard the loud beep sound that is arised in public address system.
Ever Noticed, why howling sound is produced in P.A (public address) System? Here is the reason.

The howling sound is produced when mic is brought near to speaker. This process is called "Acoustic Feedback". The Science behind this effect was first discovered by Soren Absalon Larson (Danish Scientist). Hence also known as "Larson Effect".

Public address system consists of 3 main parts:

1. The microphone to capture the sound signal.
2. The amplifier to increase the power of the signal.
3.  The loudspeaker to projects the signal outwards at the desired audible frequency.

Sound-Loop (Acoustic feedback)

The main cause of this is the creation of sound loop by all the above component.
If a person taps on the microphone in front of the speakers, the reverberation travels through the mic, into the amp, and out of the speakers.  The continuous sound created by the initial resonance that ends up coming out of the speakers is then picked up by the microphone, which creates a circular audio loop that amplifies its own frequency—and creates the uncomfortable, high-pitched screech known as feedback.

Resonance is created between mic and speaker. 
This effect can be minimized very easily. Nowdays equlizer is used to avoid this nuisance sound in PA system. It can also me minimized by placing speaker far away from the microphones.The other simple way to cut down on feedback is to always position the loudspeakers in front of and pointing away from the microphone so the loop can never complete itself.

Positive side:

"The Beetles" were first to use acoustic feedback intentionaly in their concerts and now its has beocome a trend.

This sound is very irritating to our ears. but it has been intentionally used by various musicians over the years onstage or on their records. The first instance of intentional feedback on a song was in the introduction to the Beatles classic “I Feel Fine”.

Source: Wikipedia (Audio Feedback)

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