Primo EM172 for < 20Khz with Primo EM179 in front of the EM172 works very w=
ell for ultrasonic frequencies around 22 Khz (dog devices) - the EM179 is a=
right -expletive removed to comply with nature recordists policy- to solde=
r due to its size, an aluminium block is required to dissipate the heat dur=
ing soldering otherwise you risk damaging the diaphragm or desoldering the =
fet on the reverse side of the pcb. SNR of the EM179 isnt brilliant.
Alternatively smarter materials can be used, either as rectangles, or wrapp=
ed into cylinders which provide more omni directional response (at least in=
the horizontal plane)
http://www.urlme.net/blog/?p=3D1566#more-1566
http://www.urlme.net/blog/wp-content/uploads/2010/09/keys.jpg
Bottom line buy Raimunds products - they are designed for the job, purchase=
right once...
-M
--- In "Raimund" <> wrot=
e:
>
>
> > Raimund,
> >
> > I notice the Avisoft mics use Knowles capsules and I've tried several
> > of these with some success up to 120KHz. They need a little
> > equalisation and this brings up the hiss above 80 KHz. I've tried to
> > minimise this with a home designed impedance matching preamp but that
> > experimatation has stagnated a bit looking for the ideal op-amp.
> >
> > Several commercial bat detectors use Knowles capsules, but they also
> > tend to be hissy, but if that is not a problem Knowles may the
> > affordable solution to recording ultrasound. They use the same circuit=
> > as any other electret capsule.
>
> David,
>
> Yes, those electret microphones are a bit hissy at ultrasonic frequencies=
and the their frequency response is not really optimal. But as far as I kn=
ow, this would be the last expensive solution.
>
> Better results can be achieved with a true condenser microphone such as o=
ur CM16/CMPA model that is also available as a phantom-powered version (see=
http://www.avisoft.com/usg/cm16_cmpa.htm).
>
>
> > I can't find a freqency spec for the E-MU products and I fear that as
> > audio devices, they may well limit the bandwodth to avoid problems
> > within the audio region. The last thing you need in any audio setup is=
> > interference from a source you can't hear. Digital buses can be a
> > nightmare. 192s/sec gives a much cleaner audio top end, but not
> > necessarily a higher frequency range. If anyone knows otherwise, I'd
> > be interested for bat work.
>
> I have tested the E-MU Tracker Pre thoroughly and it works fine for this =
application. It is also being used successfully by a number of clients for =
bat monitoring applications at wind energy facilities.
>
> Its analog bandwidth is about 80 kHz and there are no digital buzzes. The=
preamplifier is however not very quiet, but this does not matter in conjun=
ction with these ultrasonic microphones.
>
> Regards,
> Raimund
>
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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