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Re: sound wavelengh and parabola size

Subject: Re: sound wavelengh and parabola size
From: Walter Knapp <>
Date: Mon, 17 Feb 2003 22:45:13 -0500
Jim Morgan wrote:
> OK, I repeated the test using 11 different frequencies, 50, 60 70, 80, 20=
0
> 400,
> 800, 1500, 3000, 6000 and 12000.
>
> BUT I recorded with the low frequency mic filter off. The first test was
> with it on and that is what reduced the low frequency gain. For those of =
you
> not familiar with the Telinga it has a filter that reduces low frequency
> noise and you can record with it off or on.
>
> The gain on this second test was fairly even except for the 6000 Hz porti=
on
> which for some reason was a bit low.
>
> So according to my test the frequency gain changes very little.
>
> I know this is sort of a silly test but it was fun and gives me a little
> better understanding of what my equipment is doing.

Did you get good enough figures to know what sort of dB drop the low
frequency filter is giving you at each of those bottom frequencies? I
believe you said it looked exponential.

I record nearly always with this filter on, because it's supposed to go
into effect at frequencies lower than any of the frogs I'm interested
in. And it does get rid of a lot of low frequency noise.

Informal tests like this are always interesting. And that's why we do them.

Walt




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