An analysis of low frequency noise from large wind turbines

As wind turbines get larger, worries have emerged, that the noise emitted by the
turbines would move down in frequency, and that the contents of low-frequency noise would be enough to cause significant annoyance for the neighbors. The sound emission from 48 wind turbines with nominal electric power between 75 kW and 3.6 MW was analyzed. The apparent sound power, LWA, increases with electric power at a rate close to 3 dB per doubling of electric power. The low-frequency proportion (10-160 Hz) increases more rapidly, and the difference in slope is statistically significant. A comparison of one-third-octave-band spectra shows that the relative noise emission is higher in the 63-250 Hz frequency range from turbines above 2 MW than from smaller turbines. The observations confirm a downward shift of the spectrum.