Hi Rob,
I am not sure if this will help with your project but at any rate I found t=
his paper very interesting - and certainly a must read for anyone with inte=
rests in natural quiet and ecosystem acoustics:
The Costs of Chronic Noise Exposure for Terrestrial Organisms
Jesse R. Barber, Kevin R. Crooks, Kurt M. Fristrup
Trends in Ecology & Evolution, Volume 25, Issue 3, March 2010, Pages 180-18=
9
Abstract can be found here:
or http://tinyurl.com/6h89aqg
Full text pdf, I found online here:
http://tinyurl.com/5w8kubz
One passage (from page 7 of 10) that could pertain to your transmission noi=
se research follows:
=E2=80=9CAdventitious sounds of insects walking contain appreciable energy =
at higher frequencies (main energy ~3=E2=80"30 kHz) and are thus unlikely t=
o be fully masked by most anthropogenic noise (<2Khz) but the spectral prof=
ile near many noise sources contains significant energy at higher frequenci=
es. Foundational work with owls and bats has shown that frequencies between=
approximately three and eight kHz are crucial for passive sound localizati=
on accuracy.=E2=80=9D
It seams to me like low frequency transportation noise combined with high f=
requency transmission line noise could squeeze usable natural quiet into in=
to a relatively narrow band.
John Hartog
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