What causes that howling sound in PA systems?

A public address system's speakers emit strange noises, or feedback, when sound gets re-amplified. Get a detailed explanation of how feedback occurs in this podcast from HowStuffWorks.com.A public address system's speakers emit strange noises, or feedback, when sound gets re-amplified. Get a detailed explanation of how feedback occurs in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how stuff Works dot com
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(00:25):
today's question, what causes that howling sound in p A systems?
A simple p A or public address system consists of
a microphone and amplifier and one or more speakers. Whenever
you have those three components, you have the potential for feedback.
Feedback occurs when the sound from the speakers makes it

(00:47):
back into the microphone and is re amplified and sent
through the speakers. Again. Imagine that you place the microphone
in front of a speaker. Now you tap on the microphone.
The sound of that tap is through the amplifier, comes
out the speaker, and it re enters the microphone. That
cycle repeats over and over. This loop happens so quickly

(01:09):
that it creates its own frequency, which we hear as
a howling sound. The distance between the mic and the
speaker has a lot to do with the frequency of
the howling, because that distance controls how quickly the sound
can loop through the system. If you're setting up a
sound system and you want to avoid feedback, there are
a few general rules that can help you avoid the problem. First,

(01:32):
make sure the speakers are in front of the microphone
and pointing away from the microphone. If the speakers are
behind the microphone, then feedback is nearly guaranteed. Second, use
a unidirectional microphone. Third, place the microphone close to the
person who's speaking or performing, And fourth, if you have
access to an equalizer, dampen the frequencies where feedback is occurring.

(01:57):
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M HM