Very interesting. It's going to be difficult to track down, but could be co=
ming from the nearest village which is 6 miles away to the south where ther=
e is a paper factory. I used to live next to that factory and spent months =
working with them to dampen the sound of a new air circulation system they =
had installed that was really obnoxious. A generator is also possible becau=
se many folks around here are off the grid, but I wouldn't expect that to b=
e so constant. I'm amazed.
It's also curious that my "tinnitus" is exactly one octave above this rumbl=
e. It's a very different quality of sound, much more focused, and I can't h=
ear it in my recordings, so probably unrelated, but curious nonetheless.
John
--- In "Avocet" wrote:
>
> >I wonder if it is an acoustic feature of the valley. My next
> > experiment will be to get out of this valley and see if I still
> > record this rumble.
> >
> > Any thoughts?
>
> John,
>
> If it is a constant frequency the odds are that it is man-made as Dan
> suggests. It could be a resonsnt effect - which I have at the back of
> my house when a plane flies past at one particular direction. At 45Hz
> you would be looking at dimensions around 7.5metres or 25 feet. It
> could be catching a roof cavity or just spaced walls. (A low frequency
> grating filter)
>
> If it is wind energised, the level would fluctuate, but a more
> constant sound would indicate a mechanical source. Land topography and
> wind shear could focus a distant source. Air absorption at these
> frequencies is very low but could mask more recognisable engine
> noises. The source could be miles away.
>
> It sounds an interesting puzzle and recordings elsewhere in the valley
> and on the edge could give clues. I live in a valley and it is
> normally very quiet, but under some atmospheric conditions I can hear
> village noises well over a mile away at the foot of the valley.
>
> David
>
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce
>
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