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How screen electret mic beside cellphone?
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| Fred McKenzie 2006-05-22, 4:21 pm |
| In article <Xns97CBF290D53971F3M4@127.0.0.1>, Alex Coleman
<no@no-email.com> wrote:
> I have an electret mic which I want to use close up to a cellphone to be
> able to hear the sound in the earpiece.
>
> How do I screen it to avoid interference?
Alex-
Have you tried a magnetic pickup coil instead of the electret microphone?
If the phone is hearing-aid compatible, there should be sufficient
magnetic energy present. With this approach, there would be no direct
acoustical sound picked up.
Even if you could completely shield the pickup or electret microphone, you
must also shield the cellphone's microphone. A percentage of transmitted
audio is fed back to the earpiece to give the user confidence that they
are talking loud enough, and that the phone is working. That percentage
is called "side tone". The side tone would contain any background noise,
and would be coupled to your pickup or electret microphone along with the
received audio.
Fred
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| realradioham 2006-05-22, 6:21 pm |
| Try a small ceramic surface mount cap directly across the microphone
terminals, if you are feeding the mic into a cheap recorder you may also
find the problem is with breakthrough in the recorder itself. A few small
ferrite beads on the cable will help.
hth
rrh
"Alex Coleman" <no@no-email.com> wrote in message
news:Xns97CBF290D53971F3M4@127.0.0.1...
>I have an electret mic which I want to use close up to a cellphone to be
> able to hear the sound in the earpiece.
>
> How do I screen it to avoid interference?
>
> I know companies like Olympus can manage it because they have an in-ear
> mic to record mobiles.
>
> http://www.teknikmagasinet.se/prod/stor_bild/290080.jpg
>
> http://www.ndeva.co.uk/index.php?10...103&begin_at=20
> &tt_products=422
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"Alex Coleman" <no@no-email.com> wrote in message
news:Xns97CBF290D53971F3M4@127.0.0.1...
>I have an electret mic which I want to use close up to a cellphone to be
> able to hear the sound in the earpiece.
>
> How do I screen it to avoid interference?
Put it into a small metal enclosure, with some very small holes in it to let
the audio in. The metal enclosure needs to be connected to the ground braid
on the audio cable.
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