Noise and Pressure Pulsations
The acoustic energy from the wind turbine was found to be:
1) Greater than or uniquely distinguishable from the ambient background levels, and
2) Capable of exceeding human detection thresholds.
This research revealed dynamically modulated low frequency and infrasonic energy from the nearby wind turbine occurring at the blade pass rate; energy which was found to be amplified indoors below 10 Hz. These dynamic infrasonic modulations were absent when the wind turbine was off. The wind turbine has tonal energy at 22.9 and 129 Hz. The wind turbine acoustic emissions were strongly coupled to the indoor environment at very low infrasonic pulsations and at the 22.9 and 129 Hz tones.
The dBA levels were inversely correlated to adverse health effects experienced; effects were more severe indoors where dBA levels were much lower (around 20 dBA). However the dBL (un-weighted) and dBG (infrasonic-weighting) levels were more strongly modulated indoors.
This increase in modulation indoors was consistent with the stronger adverse health effects indoors. The increase in total sound pressure indoors appears related to a "whole-house" cavity response; the outside pressure pulsations exciting the interior acoustic pressure much like a stick hitting a drum. Especially, the degree of negative pressure increased significantly indoors compared to outdoors.
Adverse Health Effects
This research revealed that persons without a pre-existing sleep deprivation condition, not tied to the location nor invested in the property, can experience within a few minutes the same debilitating health effects described and testified to by neighbors living near the wind turbines.
The debilitating health effects were judged to be visceral (proceeding from instinct, not intellect) and related to as yet unidentified discordant physical inputs or stimulation to the vestibular system. The dBG levels indoors were dynamically modulated at the blade pass rate and tonal frequencies and exceeded the vestibular physiological threshold guideline of 60 dBG provided by Dr. Salt.
Health effects moderated when dBG levels fell well below the 60 dBG guideline when the wind turbine was OFF. Wind turbine tonal energy at 22.9 Hz lies in the brain's "Beta" range which is associated with alert mental activity and anxiety; antithetical to sleep. The dynamic 0.7 Hz modulations of inflow turbulence and tonal energy lie in the deep Delta range associated with deep sleep. Clinical evidence of frequency following response (FFR) in the brain suggests that entrainment with wind turbine modulations, pulsations and tones may pose conflict for the brain's natural rhythms,
leading to stress when the conflicting signals (the wind turbine) cannot be turned off.
Other physiological mechanisms may be in play. Medical epidemiological field and laboratory investigation is needed. The study confirms that large industrial wind turbines can produce real and adverse health impacts and suggests that this is due to acoustic pressure pulsations, not related to the audible frequency spectrum, by affecting the vestibular system especially at low ambient sound levels.
The study results emphasize the need for epidemiological and laboratory research by medical health professionals and acousticians concerned with public health and well-being. This study underscores the need for more effective and precautionary setback distances for industrial wind turbines. It is especially important to include a margin of safety sufficient to prevent inaudible low-frequency wind turbine noise from being detected by the human vestibular system.