A report from a Canadian company is here:- http://www.canwea.ca/images/uploads/File/CanWEA_Infrasound_Study_Final.pdf
Conclusion: Infrasounds (sub-audio) are present, but at safe levels
Merge, please, the following two phrases together:
1) After thinking about it last night,
2) Much as I don't like to throw a damper on anything that might help free us from fossil fuels,
..... I am forced to conclude that the noise produced by windmills might be more detrimental than some might think.
The ear transmits electrical signals to the brain for infrasonic frequencies as much as it does for audible frequencies. You can therefore assume that the brain experiences as much excitation and it results in just as much stress. The only difference is that you can't listen to infrasonic frequencies -- each oscillation takes so long that you've forgotten the beginning of it before it reaches the end (humans can only aggregate sensory impressions for about 50 microseconds.)
According to the study, some of the windmill installations increased the ambient infrasound levels by about 20 dB compared to just the wind. That might not look like much, but remember that it represents 99% of the sounds' power.
I don't know about you, but I find windy days kind of creepy. Maybe it's the implied threat of the wind's force, or the sound of it hitting the trees, or maybe the ions it produces, or all of the above, or perhaps it could also be the unsettling effects of the infrasound. If that's so, I wouldn't want to increase it.
Most green technologies that I can think of produce less noise than their conventional counterparts. Maybe wind turbines should only be located quite far away from residential areas.
Again, I like the idea of little mini turbine pinwheels arrayed on the surface of buildings, if that's possible. Those can be imagined to produce nothing more than a sound similar to leaves.