Low Frequency Noise 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.
Library filed under Zoning/Planning from Michigan
Shadow Flicker Shadow flicker is caused by the sun rising or setting behind the rotating blades of a turbine. The shadow created by the rotating blades can cause alternating light and dark shadows to be cast on roads or nearby premises, including the windows of residences, resulting in distraction and annoyance to the residents. A related phenomenon, strobe effect, is caused by the chopping of sunlight behind moving blades, similar to the effect of the setting sun behind trees when driving along a roadway in the winter. Both of these phenomena are factors in the visual impact of a wind turbine project, and some argue that they are a threat to health and safety. They could also be considered a nuisance to nearby property owners.