HI Raimund:
At 08:51 AM 4/8/2003 +0000, you wrote:
>As we have seen recently, a parabolic dish should work satisfying at
>higher frequencies, especially in the ultrasonic domain (where the
>dish could be smaller). Reflections and resonance within the
>microphone capsule are responsible for the distortions of the
>frequency response at the upper edge.
>
>A problem in recording fast-flying bats could be the strong
>directionality of a parabolic microphone. Several bat species (those
>feeding close to vegetation) have zigzag-shaped flight paths, where
>it would be extremely difficult to track a single bat (especially at
>total darkness). But it might be possible for species flying more
>straight ahead at higher altitudes at dusk.
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
MIST Software Associates PO Box 269, Hollis, NH 03049
EnjoyBirds.com - Software that migrates with you. http://www.EnjoyBirds.com
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