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[Nature Recordists] Odd acoustic effect

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Subject: [Nature Recordists] Odd acoustic effect
From: Avocet <>
=C2=A0
I moved my MKH416 pair the other day to near my tree-laden garden as
the dawn chorus is now hotting up. When I have time to go through the
hours of recording I'll get some up on my web page.

I had a prop plane fly past high up and as the drone dropped in
frequency, the level shot up and hit near max level at one point. I
measured an exact peak frequency - 108.6Hz. I couldn't work out what
caused this resonant point. Protective mic tent no, too soft, mic
fault perhaps? It was only on the left mic but I couldn't think of
anything that would cause such a high-Q ringing resonance and remain
stable. I went out and hummed at the mic rig at around 108'6Hz but
there was no resonance at all.

It took my old brain some time to work it out. That mic was looking
towards the house and 108Hz is equivalent to about 3 metres. There is
a single storey extension which produces two flat vertical walls about
3 meters apart. The plane sound must have produced an "echelon effect"
from the two walls. There ia no other obvious explanation.

Now I know what to listen for, the left mic does have a small bass tip
up in the general background LF noise and I can compensate for this.
However, it is an example of somtimes very noticeable effects we can
get from nearby objects.

David

David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce














"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.



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