sound produced by loudspeaker

January 14, 2011 at 03:08:49
Specs: Windows XP

Why the sound produced by loudspeaker not picked up by the mic in a cellphone???

If the cellphone is on loudspeaker mode, then the sound received from the loudspeaker should go to the mic and it should be received from the loudspeaker again. however it doesnot happen..why ?

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January 14, 2011 at 04:29:52

If what you are describing where allowed to happen you would get what is known as acoustic feedback which results in an screeching noise with an ever increasing in volume. Try plugging a microphone in to a hi-fi and turn the volume up and you will see what I mean.

There are circuits in mobile phones to prevent this from happening.


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January 14, 2011 at 06:56:31

Mic pics up all the surrounding sounds...nearer to mic and even those which are far away from the mic...then why not it picks up that produced from loudspeaker....though in a cellphone loudspeaker is closer to mic only....anyways..i just want to know how it is prevented and what kind of software is used internally to prevent it...and how it functions?

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January 14, 2011 at 07:12:20

It isn't done in software, it is done in hardware. There are filters that can recognise the difference between random noise and the repeating noise going round in circles from speaker to mike.

If you really want to know how it works read this then take it from there.


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January 14, 2011 at 09:53:26

Quite helpful. Thanks !

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