> 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 know, this
would be the last expensive solution.
Better results can be achieved with a true condenser microphone such as our
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 conjunction
with these ultrasonic microphones.
Regards,
Raimund
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