> I have not yet looked into the actual altitudes, but considering I
> usually record at least 200 miles from the nearest major airport,
> these flyovers must be 10 thousand feet or higher(just a guess),
John,
Jets are at a cruising height over me at about 35,000ft or about 10
kilometers. I've got a set of graphs of air absorption at various
frequencies and it comes out as around -10dbs below 200Hz but -70 dBs
down at 1KHz. That's in addition to the drop due to distance. The
distance drop from 100 metres to 10km is another 40dB, say 100
dBA -40dB -70dB at 1KHz. The audibility limit happens somewhere in
between 200 Hz and 1KHz.
That's the theory - the practice is that the jet noise is well down at
bird tweeting frequencies and cars a mile away are more of a problem
here.
I'm fortunate to be mostly under transatlantic flights, but as I said
height is crucial to jet noise.
Concordes used to go subsonic over the Bristol Channel but
occasionally caused a sonic boom which would spook all the pheasants
in the area in unison. :-)
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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