Ranft, Richard wrote:
> Dear Pratap
>
> The relationship between sound wavelength and parabola diameter is probab=
ly
> more important than parabola focal length, in that parabolas simply won't
> reflect sounds whose wavelength is greater than the parabola diameter. I=
n
> effect, the parabola has a severe bass cut below a frequency determined b=
y
> its diameter.
Then perhaps you will explain how my Telinga (20") reflects sound down
all the way to 50 hz? The Telinga is directional and has better than
unity gain all the way down.
It would be really nice if parabolas act as low cut filters with a sharp
cutoff, but they don't. No matter what physics thinks happens. I have to
apply a cutoff filter separately. Just below the lowest frequency frogs.
What happens is the gain falls off at low frequencies, it's not cut off
sharply.
> The parabola is better for recording the
> higher-pitched sounds especially those that are far away, and is more
> directional, but I use a gun mike when recording larger birds or mammals
> because its frequency response extends into the lower frequencies. Many
> times when recording in remote places I find I have taken the 'wrong' mik=
e
> out on a recording session and the more appropriate one I left back at ca=
mp!
A shotgun mic is ok for closer stuff, but it's very hard to get a lot of
reach out of one without self noise. Even at low frequencies.
I use the Telinga on Bullfrogs, Pig frogs, River frogs, Gopher frogs,
Green frogs, and Barking treefrogs (as well as lots of other, higher
frequency species). All those have their major call energy in
frequencies way below the theoretical 650hz of the dish. I have recorded
Barking treefrogs from distances measured later as greater than a mile.
Some of the others nearly as far. And that's with the DAT Stereo mic
element.
As you say, it's tricky to always have the right mic. But if I could
take only one mic for call recording, it would be the Telinga. My
MKH-816's would be down the list a ways.
Oh, and I have recorded owls incidental to my frog recordings. Often
quite distant calls. The bird survey folks seemed happy with the
recordings. Not enough people recording night birds.
Walt
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