Low frequency noise from wind turbines
Wind turbine noise can contain both low and high frequency noise. Most noise is caused by the rotation of the blades and is high frequency, but low frequencies also generated noise.
The Environment Protection Agency has revised the Statutory Order on Wind Turbines to include mandatory limit values for low frequency noise.
Low and high frequency noise
Wind turbine noise covers a broad spectrum of frequencies including deep and high pitch sounds (low and high frequencies). Most noise is caused by the rotation of the blades and resembles a periodic swish. Blade noise is strongest at high frequency, but the blades' rotation also generates low frequency noise.
The turbine's machinery components (gears and generator) also emit noise, which can contain a high pitched wailing (at high frequencies) or humming or rumbling sounds (at low frequencies). Wind turbine noise does not feature stronger low frequency sounds than for instance traffic noise.
Infrasound is sound at a very low frequency
Sound at very low frequencies is called infrasound. In contrast to earlier understanding of the subject, infrasound can be heard or perceived if it is strong enough. When infrasound is discernible, it is often annoying. Infrasound that is lower than hearing or sensory limits is not discernible and cannot harm health.
Wind turbines emit infrasound from the rotation of the blades. The wind turbines we know in Denmark have blades mounted on the wind side of the tower. They emit so faint infrasound that it is not audible, even close to the turbine.
Read more about noise from wind turbines
Read also Q&A on low frequency noise from wind turbines