Posted by: "Jim Morgan"
> A parabola can work for this but keep in mind that the distant sounds you=
record will likely have a distant sound quality to them. I believe this is=
primarily due to the attenuation of the higher frequency sounds caused by =
the distance. The porabola will compensate for this, to a degree, by amplif=
ying the higher frequency sounds more that the lower frequency. In fact the=
lower frequency, if low enough won't be amplified by the parabola at all.
The lowest frequency for gain from a parabola is not far from the lowest
frequency of our hearing. Though this is a often misunderstood area. For
low frequency work with a parabola you should really have one with the
focal length well shorter than the dish depth. This avoids interference
from the standing wave that set's up from the reflections off the
parabola. And as gain is small at low frequency a larger dish does help
a little.
The gain of a parabola does vary with frequency and does approximately
compensate for high frequency loss with distance. At least for some
distance ranges. The Telinga site has a white paper discussing this. To
find out if you like the sound your best bet is to try it.
So it all depends on what you really want. You can get a clear
recording of something 200 feet away but it will have a distant quality
that one 50 feet will not have. If you are a wiz at sound editing you
might be able to correct this.
Any mic setup other than a parabola will have a far greater distance
effect. And for soft sounds will need a lot more gain. So it will have
to be a much more sensitive mic with much lower self noise to give as
clear a recording as the parabola. For most mics you must be close.
Note to avoid the parabola picking up sounds from beyond your point of
interest have it up high pointed at a downward angle at your sound
source. It's narrow pickup will then be focused on the area of interest
and little else. If you point it horizontal you can have interference of
other sounds from as much as a mile or more away.
Walt
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