when we were children, there used to be a lot of 'table fans' around. one e=
ntertainment was to sing loudly into the fan, while it is spinning. at some=
distances, it would break the voice up in very interesting ways. i think t=
his is a similar effect, happening at very low frequencies and probably at =
high amplitudes.
umashankar
i have published my poems. you can read (or buy) at http://stores.lulu.com/=
umashankar
----- Original Message ----
From: Mark Fischer <>
To:
Sent: Sunday, October 7, 2007 9:00:24 AM
Subject: [Nature Recordists] An un-recordable sound, re-visited
Dear Nature Recordists,
A while back I posted about an un-recordable sound I had heard, a
mile+ downwind of some of the largest windmills in the world... doing
the math lead to numbers that did not make much sense, as far as prop
rates, and the resultant frequencies of any generated waves... and,
yet, there was a sound, coming from these windmills...
Well, today, I was downwind, maybe a quarter mile, of a single, much
smaller windmill (not a whole field of giants, with the possibilities
of harmonics, constructive and destructive interference, and so on)
and watched the sound being made.
No kidding.
It appears to be an interaction between the blades and the tower. As
each blade passes in front of the tower, in interferes with the
windflow. On/off, On/off, what results is a wave of pulses downstream
from the tower. The blades do not make it, by themselves. The tower,
by itself, makes no sound. Put the two together, in a steady breeze...
Of course, I did not have my recorder with me. But now I know what
conditions bring this about. I bet there is some function
(relationship) of the distance between the blades and the tower, and
the wavelengths of the resulting sound.
Stay tuned...
Mark
~~~~
"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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