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Significance of the results from the EARS project on wind turbines

11.08.2015

To understand the influence of infrasound on humans it is necessary to study the perception mechanisms of infrasound. For this reason, the project EARS combined physiological with psychoacoustic methods. All measurements were made in a laboratory setting using synthetically generated sound and a normal population of subjects. The acoustic stimulation was not derived from and not related to wind turbine sound. The mathematical model to generate the acoustic stimuli was not based on wind turbine acoustics. The sound was delivered to the ear canal only and there was no vibrational coupling to the human body other than the ear canal.

To have a controlled acoustic stimulation for all subjects, the hearing threshold and the loudness scale was determined for each subject individually. These psychoacoustic results show statistically significantly, that sound is perceived with the ear down to 2.5 Hz if the sound pressure level is high enough. The hearing thresholds and the loudness scales are consistent with literature data and can be found in a project report.

Subsequent physiological measurements using repetitive acoustic stimulation at sound pressure levels high enough for easy perception showed a significant activation of the auditory cortex down to 8 Hz in fMRI and down to 20 Hz in MEG. No activation was found in the auditory cortex for sound pressure levels below the individual hearing threshold. This means that below the hearing threshold no activation occurs in the auditory cortex for short duration stimulation in the range of seconds. This combination of physiological and psychoacoustic parameters from individual subjects is completely novel. A follow-up experiment in the fMRI used a 200 s acoustic stimulation at levels in the vicinity of the hearing threshold. It was found that brain areas related to emotion processing are activated. This does not imply any quality of the emotion, neither positive nor negative, neither fear nor joy, for example. Any conclusion that wind turbine noise triggers a specific emotion cannot be drawn at all from our results.

The acoustic exposure in our study was not derived from real sound fields occuring in the vicinity of wind turbines and therefore absolutely no conclusions in relation to wind turbines can be drawn. To draw conclusions in this direction, the experiments would need to be repeated using real sounds for stimulation, but the present results are the basis for being able to interpret future experiments using real sounds.

If a person indicates annoyance possibly due to an acoustic source (not necessarily a wind turbine), a quantitative audiological assessment of that person is needed, as was done in our controlled study. General conclusions cannot be drawn at the moment. Independent of individual perception, new work is being done using statistical methods to define thresholds adapted to particularly sensitive persons. Here “sensitive person” refers to a person with a still-to-be-defined low perception threshold for infrasound. If their threshold is determined, it is statistically certain that annoyance will be avoided.

The results from the present study indicate future directions of research: Not only are objective hearing thresholds important, but individual annoyance needs to be quantified in a reproducible manner. This approach might yield new thresholds.

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Opens window for sending emailChristian Koch, Opens window for sending emailTilmann Sander-Thömmes