Posted by: "jpbeale"
> Not sure where to post this, would it go better on the micbuilders list?
I'd suggest rec.audio.pro or a similar group.
> I would like to measure the self-noise of some of my microphones. I
> have a very rigid airtight enclosure which I suspect has high enough
> attenuation to be useful, but the interior space is fairly small.
>
> My question: should I expect the noise output from a microphone that
> is closely wrapped in felt to be the same as the noise when there is
> more open airspace around the mic, assuming in both cases negligible
> external acoustic noise? The only difference I can think of is
> thermal convection currents, which I hope are too small to measure.
> Are there any exotic effects I might be missing?
You could listen to the quality of the self noise this way, and it is
important to compare that. But to measure the self noise you need to do
so against a standard sound level. Normally a precise 94dB (or 94dBA)
sound source is used. You set the metering to zero that sound level,
then turn off the sound and the reading you get will give you the self
noise. You will not be able to do that measurement with a wrapped mic.
If you are not familiar with the Microphone Data website you should be.
This is a website supported by all the mic manufacturers, and hosted by
Rycote. It has the latest data on all current mics. Or at least tries to
be that complete. Probably won't be good on cheap low quality consumer mics=
.
http://www.microphone-data.com/default.asp
The site is free, though you do have to register for access.
It also has a library of articles several of which should be read by
everybody, particularly those thinking they can casually set up test
systems that will give better data than is available. Here's a few I'd
suggest for starters:
Microphones, preamps and impedance (pdf)
The interpretation of the microphone data sheets (pdf)
Choosing the right microphone (pdf)
Getting techno-physical (pdf)
Microphone powering (pdf)
Shields, grounds and microphone cables (pdf)
How to reduce wind noise and vibration (pdf)
None of these were written with outdoor nature recording in mind, but
are generally useful. Mostly they are a light brush on each subject.
Walt
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