> [this type of low frequencies produces
> discomfort.] Often the receiver is not aware of what is happening, he only
> feels bad (e.g. nausea). This sometimes happen close to wind farms, but
> very few studies focus on infra sounds and the beats of multiple infrasound
> sources. I recently attended a conference session on the measure of wind
> farm noises (on land, not marine) and all studies presented were made with
> phonometers with the "A" weighting curve. Some hearing test were made with
> headphones, completely forgetting the ability to perceive infra sounds
> with the body.
Gianni,
A few years ago I wrote a submission for a wind farm protest group. The
noise data quoted by the wind farm lobby used "standard" B&K noise meters
with A-weighting but there are other disturbing noises which were not being
discussed.
One of these is secondary wake noise. A spiral wake travels downwind from a
large turbine for a kilometre or more, but this doesn't itself make much
noise as in consists of stable toroids of turbulence energy. This is very
similar to the wake of an aircraft which should not be a surprise as
aerodynamic turbine blades move at light aircraft speeds.
However when this turbulence hits trees or a house, they release the energy
as pulses of whooshing at one second intervals which is very difficult to
sleep through. A-weighted measurements are meaningless in this case.
My pet hate is when one car window is opened and a low frequency
reverberation sets up. As you say, you "hear" this with your whole body.
David Brinicombe
"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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