Noise from wind turbines The Swedish EPA provides guidance on the calculation and measurement of sound from wind turbines as well as target values. An important question relating to permits and registration for new wind turbines concerns how high the sound levels are allowed to be. svenska Share Contact Listen Much of the sound a wind turbine makes comes from the rotor blades passing through the air. This sound is usually perceived as a hissing or swishing sound. The sound can be described as a broadband noise, usually within the frequency range 63–4,000 Hz. The sound level decreases with the distance from the wind turbine. The weather and wind affect how the sound propagates. Even the type of soil or the presence of water at the wind turbine affects how much the sound decreases with distance. Generally, the ground dampens the sound much more effectively than water does. Variation in how we perceive sounds How well we hear and perceive the sound from wind turbines varies widely. This is due to variations in wind strength, the meteorological conditions and other sounds in the environment that can mask or reduce the audibility of sounds from a windfarm. How much we humans are disturbed by sound also varies – from day to day, from place to place, from individual to individual. This means that it can be difficult to measure and calculate the sound in a way that gives a representative picture of the wind turbine sound and to assess how annoying the sound will be. Studies conducted on annoyance have often assumed a calculated sound exposure at a wind speed of 8 m/sec at 10 m height at the wind turbine, in accordance with standards. This sound level can therefore be considered as a reference value for annoyance without representing the actual average exposure over a period of time. Low-frequency sounds Today, there is no evidence that the low-frequency sounds from wind farms pose any risk to local residents. But for the wind farms that have been built so far and where some research has been conducted, the value is usually less than 2–3 megawatts. The larger wind farms as planned today could deliver slightly more low-frequency sounds. See also More Information. Low-frequency sounds are important to consider Low-frequency sounds affect people more than sounds that are not dominated by low frequencies. Examples of symptoms during exposure to low-frequency sounds are fatigue, headaches and disturbed sleep. The symptoms and problems can appear even at low volume levels, just over the normal hearing threshold. Low-frequency sounds have a longer wavelength and are therefore more difficult to dampen, and they can also propagate over longer distances than other sounds. The EPA therefore believes that the major wind farms should take into account and follow up on low-frequency sounds. A rather easy way to assess whether there are low-frequency sounds is to find out the difference between A-weighted (see More Information) and C-weighted sound levels. It is likely not a problem if the A-weighted level is well below the target value at the same time as the difference between the C-weighted and A-weighted sound levels is less than approximately 20 dB. If the difference is greater, on the other hand, then a more accurate measurement should be taken. The Public Health Agency of Sweden offers general advice that includes guidelines for low-frequency noise indoors; see More Information.