the wavelength at 48 kHz is 0.73 cm or 7.3mm, just a bit more than the
diameter of the capsules or the spacing among the center of two capsules.
This means that only ultrasounds coming frontally will sum up in phase.
As for the heterodyne detectors, I would discourage using them. They
produce an audible output signal only when the incoming signal is few kHz
around the selected frequency thus producing a highly partial and distorted
output signal. Bat detectors based on frequency division are for sure much
better. The best option remains the full bandwidth recording and then the
slow speed playback to make them longer and lower in frequency, thus well
audible by our "slow" ears.
If you plan to use the F8, then you can use multiple microphones to record
a wider space or use additional widely spaced mics to understand the flying
direction of the bats. Probably you can easily adapt the powering scheme
P48 to PIP (described in other posts) to power the EM258 from the F8 P48.
Gianni
2018-02-26 10:10 GMT+01:00 [naturerecordists] <
>:
>
>
> Good point, Gianni. At those shorter wavelengths, capsule spacing starts
> to matter a lot more. Mexican free tailed bats call between 40 and 75kHz.
> At the low end, around, 48kHz and 20C temperatures, the wavelength is onl=
y
> 7.3cm. The EM258 capsules are 6mm in diameter, so basically I'd be right =
in
> the mess of things, and it would only get worse at the higher frequencies=
..
> I'll build these using one capsule per channel.
> http://mammiferimarini.unipv.it
>
"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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