The Windfarm perception project shows that the sound of wind turbines causes relatively much annoyance. The sound is perceived at relatively low levels and is thought to be more annoying than equally loud air or road traffic. This may be caused by the swishing character of the sound or because at night it does not decrease in strength -which is usually the case for traffic noise. Also in this study more disturbance of sleep occurs at the highest sound levels that occurred in this study. ...In the WINDFARM perception project, supervised by Frits van den Berg, the perception was investigated of modern, tall wind turbines by Dutch residents. The study shows that sound from wind farms is an important disadvantage of wind energy which in itself is positively appreciated by a majority of the participants.