> How "loud" is a 65dBA in a natural habitat?
Rob,
Exactly 65dBA. The problem is that "acceptable" levels are set by people
with no knowledge of sound. For instance a random natural noise of 65dBA, o=
r
a waterfall, or a seashore, could be argued to be acceptable.
However a single frequency noise, or a pulsing noise, or a low frequency
hum, all at 65dBA, can be exceedingly irritating to human ears. Also we hav=
e
little data on how noise affects wildlife.
The A-weighting curve does not give a true indication of how noises affect=
human perception. At 60Hz, the A-weighting curve is at around -27dB, meanin=
g
that the actual sound level is 27dB higher than indicated on a sound level=
meter, and 65dBA becomes about 92dB - which could be damagingly loud. This=
can make nonsense out of A-weighted noise meters.
The effect for us recordists would be worse, as the inverse square law only=
applies to a point source, and a transmission line is not a point source an=
d
would carry more at a distance.
What is also not measured is ultrasound, and high voltage transmission line=
s
give off ultrasound from corona discharges which can get quite noisy when
damp. This doesn't carry well with distance but it could have an adverse
effect on wildlife locally. Not only bats but some birds use ultrasound
detection. A bat detector will show this noise up.
I've also looked into an example of subjective noise disturbance with wind=
turbines. I made a submission to a Public Inquiry over induced secondary
wake noise. This is when turbulence pulses at about one a second meet a tre=
e
or a house, where locally they generate a regular swooshing sound but which=
are not measurable in free air with a meter, but which can make a house
uninhabitable.
David Brinicombe
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