Re: Capturing EM interference with a microphone
- From: jh <no@xxxxxxxxxx>
- Date: Fri, 04 Nov 2005 17:03:09 -0500
Thanks for everyone for your ideas. I'll try some stuff (when I get a
chance; it might be a while) and post anything interesting. I'm hoping
to eventually (maybe after I learn more about electronics) build a
reasonably sensitive EMI-only "microphone" to use as a sort of computer
stethoscope.
Here's my idea: could a computer technician, with this tool and some
practice, hear and immediately recognize the EMI signature of a dying
power supply or other bad component, the same way an expert pilot can
instantly diagnose engine troubles just from their noises? Certainly,
many technicians can recognize the distinctive sound made by some dying
hard drives; but most components don't make any noise that we can hear
naturally.
-- Josh
In article <1131113675.779200.106750@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
hrhofmann@xxxxxxx wrote:
> Jasen Betts wrote:
> > On 2005-11-04, jh <no@xxxxxxxxxx> wrote:
> >
> > > The only problem is, all of these great interference-caused phantom
> > > sounds were almost drowned out by the actual normal sound produced by
> > > the fans, hard drive, etc. in the computer. Needless to say, the
> > > microphone was quite adept at recording these sounds.
> >
> > the reason for that is that the dynamic microphone has a voice coil (like
> > in a
> > loudspeaker) anf that coil picks up all the electromagneic interferance
> > (EMI)
> > inside your computer.
> >
> > > So my question is this: is it possible to build a device, or modify a
> > > microphone, so that it picks up ONLY the electromagnetic interference,
> > > but no actual sound?
> >
> > You'll need to shield it against EMI. while not blocking too much sound
> > that that won't be easy. basically you need to surround it with a
> > conductive
> > shell, electret mikes (like the "ctrappy lapel mike") are constructed that
> > way.
> >
> > Bye.
> > Jasen
>
>
> Jasen and OP:
>
> You want to pick up the EMI and not pick up the acoustic sound. The
> best way to do that is to replace the microphone with a plain coil of
> wire. The coil will pick up the electronic/electromagnetic
> interference and not pick up the acoustical noise. You could also do
> that by immobilizing the moving part of the microphone so that it only
> picks up the EMI and does not respond to sound. That is just the
> opposite of what most people want, but having done EMI work for many
> years, the sounds of something working are very interesting. If you
> have an old LED display pocket calculator, try using that as a noise
> source, Listen to the difference between adding two numbers and
> getting the logarithm of a number, for example. You can hear EMI noise
> also from almost anything electronic.
>
> One other possibility for just a very short time would be to stop the
> fan on your computer to stop the acoustic noise, SInce you have the
> computer out of the case already, you could probably run without a fan
> for a minute of two. Just don't stop the tiny fan on the processor
> chip if your computer has one of those.
>
> H. R.(Bob) Hofmann
>
> H. R. Hofmann
.
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