> Bill R. wrote:
> Any impression of the noise/sensitivity of the
> AT3032 above 20 kHz?
In my original measurements of my sample of the
AT3032, I found that the HF response was down about 2
dB at 20 kHz. It's definitely starting to roll off at
that frequency. On the other hand, its noise
performance is quite flat up to 20 kHz. Some
microphones have noise spectra that are tilted
spectrally, but not this one.
The real problem that I see is that even a "small
diaphragm" microphone like the 3032 is pretty
directional at 40 kHz. You would have to be pointing
the microphone right at the bats. And the bats in my
neighborhood are not very good at staying still while
you attempt to record them.
If I wanted to record bats I would try to rig
something up using the Knowles FG series capsule.
It's a hearing aid microphone, but one with very
extended HF response. It's about 3 dB up at 20 kHz,
4.5 dB down at 30 kHz, and I don't have data for 40
kHz but it appears that it would be about 10 dB down
at that point. Those numbers may not sound really
good, but there's nothing else in this price range
that has any usable response at 40 kHz.
And it's really tiny! It's 2.5 mm in diameter, which
means that it maintains polar patterns at 40 kHz which
are as good as normal microphones do at 4-5 kHz.
You can buy them for about $25 from Digikey or Newark.
These capsules aren't for the faint of heart. At
that size I require binocular magnifiers just to see
the capsule, much less solder onto the 3 tiny pads on
the back of the thing.
Since some folks don't like excessive talk about
microphones, and I've probably already gone over my
limit, feel free to contact me off-list if you have
questions about how to implement something usable with
this incredibly tiny microphone.
Eric Benjamin
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