Abstract
Annoyance ratings for artificially created noises, resembling the main
characteristics of temporal wind turbine noise, were studied by means of a
listening experiment involving 21 participants with normal hearing. Three
types of stimuli were examined: broadband noise (−4 dB/octave), noise
generated by moving cars, and narrowband noise. All stimuli had the sound
level fluctuations typical for wind turbine noise. The magnitude of the
sound level fluctuations was measured in a quantitative way, by using the
characteristics of amplitude modulated sound: modulation rate and
modulation depth. Our aim was to examine how the modulation rate and the
modulation depth influence the noise annoyance assessment of broadband and
narrowband amplitude modulated noises. Three different modulation rates,
1, 2 and 4 Hz, and sound level fluctuations (a measure of the modulation
depth), 3, 6, 9 dB, were applied to each type of stimuli (with exception
of noise generated by the moving cars) and investigated. The participants
in the listening experiment were presented with sound stimuli in
laboratory conditions and asked to rate their annoyance on a numerical
scale. The results have shown a significant difference between the
investigated conditions. The effect was particularly strong between the
annoyance judgments of different types of noise (narrow and broadband),
and modulated versus unmodulated noises. Temporal fluctuations occurring
in wind turbine noise are very pertinent to the perception of annoyance
and could be responsible for its being a relatively annoying noise source.
The obtained results were discussed and compared to the typical modulation
rates and level changes that occur in recordings of real wind turbine
noise.
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