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Re: Microphones

>> >A non-electronic solution would be to use a microphone which has its
>> >diaphram open to both sides.  In theory ambient noise cancles out (equal
>>                                ^^^^^^^^^
>> >pressure on the front and back of the diapram), but directional sound
>> >(e.g.  voice) does not.
>> 
>> In whose theory?  There is no such thing as nondirectional sound.
>
From: john flanagan <>
>Actually, Pratt is correct on this one, but perhaps isn't conveying it
>clearly.  Noise-cancelling microphones operate on the principle that the
>farther you get from a sound source, the quieter the sound (remember,
>1/r^2). NC mikes have two diaphrams, a small distance apart (less than
>1cm) from one another.

My point was that the proposed *single*-diaphragm solution couldn't work
as envisaged.  My comments weren't relevant to the two-diaphragm setup,
if that wasn't clear then what I said would certainly seem very unclear.

The only noise-relevant property of a mike with both sides of the
diaphragm open is its polar (gain or response) pattern, which (in plan
view) is a figure-eight.  Thus it hears louder fore-and-aft than to the
sides.  It will therefore "cancel" all sounds, near or far, coming from
the side but not from front or back.  It makes no distinction between
near and remote sounds other than the obvious one that remoter sounds
are quieter, which is true for all microphones.

Vaughan

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