From July 1, 2007, however, measurements of sound wave frequencies inside the house, with the windows open and closed, can also be taken into account. Again, the criteria is how much additional noise can be attributed to the turbines.
The upper limit is set at seven decibels at 125 Hz and 250 Hz and five decibels at 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. Acoustic expert Frédéric Delafosse explains that these are very complex measurements which depend on how well the house is insulated, how many windows there are and if they are double-glazed, among other things.
There is also some debate as to whether the new law should apply to turbines at all because of the very specific nature of their low-frequency sound emissions. The industry is currently consulting acoustic experts to find out if the new regulations are applicable to wind turbines or if turbines need a separate regulation.