--- In Marty Michener <>
wrote:
> If I recall from my grad work days 1962 at Harvard, Professor
Donald
> Griffin used more like a cone - a funnel -- as a reflector for bat
> detectors and bat recorders. These he said "gathered" the sound,
rather
> than focused it so accurately. This may serve better to provide
some gain
> when the aim cannot be so precise as required for a full parabola.
>
> Also, the various species of bat emit the sound quite
directionally, a
> characteristic as you know of very high frequencies. As the bat
turns
> toward you the volume is likely to increase 30 dB or more. I
would be
> tempted to use a fast-acting AGC on some of the recordings because
of the
> very variable loudness at microphone. Trying to calibrate the
sound levels
> would truly be "schrecklich".
>
> my best regards,
>
> Marty Michener
Marty,
Yes, such a funnel or tube seems be more appropriate. Very often it
is not necessary to get much additional gain, because most bats are
calling very loud (they need that high volume in order to get enough
reflected energy back to their ears) and fortunately it is often
possible to approach them very close. Therefore, one might be
surprised by the high quality of time-expanded bat calls, that were
recorded with relatively poor electret microphones. A larger dynamic
range of the recorder (12 or 16 bit instead of 8 bit) may also help
to manage the large dynamic range caused by the directional sound
emission.
Regards,
Raimund
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