Here's some notes from my own turbine.
This is a 3-metre (10') 1KW chinese job, with extruded fibreglass blades (no twist). The original readings were with the blades in their "as supplied" condition, the after was after I had re-shaped the tips and trailing edges, filled most of the holes and sanded, and a quick lick of epoxy paint...
Your milage may vary of course...
Some before-and-after noise measurements:
> In a significant gust, instruments put at 42.8KMh, while standing directly
> under the turbine I clocked 82.3dB(A) - although I don't know how much of
> that was wind noise itself.
>
> In a similar strength wind, 25 metres away, I measured 73.8dB(A)
>
> Inside, my instrument was showing "Under-Range" at 30dB(A) - I had to move
> out of the kitchen, as even the fridge was registering more than the turbine!
Just for comparison - after the changes to the blade profile as discussed,
the wind isn't quite as strong but very nearly (gusting to about 40)
Standing below the turbine, instrument on fast and A-weighted curve, I
thought more about methodology this time. Even though I had the wind guard
(foam) on, its clear the wind noise is still considerable, so given that
the turbine noise is constant over the reading interval, I figure that the
MINIMUM sound reading I see is probably the turbine noise and the short
duration peaks are probably the wind noise, I now claim:
57 dB(A) under the turbine
51 dB(A) about 25 metres away
