Low frequency noise is generated at very low frequencies, generally accepted to be at levels below 100 Hz and the audible range. There is presently no commonly accepted metric or standard for measurement, although several have been proposed or used in specific situations. Low frequency noise has been associated with wind turbine developments, as well as road, rail, sea and air traffic and other industrial applications such as cooling towers. It creates a large potential for community annoyance, and it is most often experienced inside of homes and buildings where resonance amplifies the sound, which is less easily heard outside. Because the frequencies are so low, the noise is often “felt” as a vibration or a pressure sensation. Reported effects include annoyance, stress, fatigue, nausea and disturbed sleep.
Low frequency noise can be a factor at much greater distances from the noise source than audible noise. A case study in North Carolina in the 1980’s near a wind turbine installation documented low frequency noise problems at residences located over ½ mile from the turbine.2 While the phenomenon was originally believed to be associated with the older, down-wind designed turbines, the problem persists with newer wind farms. It has received particular attention in Denmark, and has been a topic considered in the UK, Scotland and Wales through a commissioned government project in 2001.