In this paper, researchers Eja Pedersen and Frits van den Berg examine why wind turbine noise is not masked by the sound of vehicular traffic in a community. The abstract and discussion sections of the paper are provided below. The full report can be accessed by clicking the link(s) on this page.
In this paper, researchers Eja Pedersen and Frits van den Berg examine why wind turbine noise is not masked by the sound of vehicular traffic in a community. The abstract and discussion sections of the paper are provided below. The full report can be accessed by clicking the link(s) on this page.
Abstract
The possibility of road traffic noise masking noise from wind turbines was explored among residents living close to wind turbines in the Netherlands (n = 725) with different levels of road traffic noise present. No general masking effect was found, except when levels of wind turbine sound were moderate (35 – 40 dB(A) Lden) and road traffic sound level exceeded that level with at least 20 dB(A). This low masking capacity may be due to the different time patterns of these noise sources, both on a small time scale (car passages/regular blade passing) and a larger time scale (diurnal and weekly patterns). Also, wind turbine sound is relatively easy audible and may be heard upwind more often than road traffic.
Discussion
Most respondents in the WINDFARMperception survey thought the sound from one or more modern, tall wind turbines at night is louder than or not very different from the sound in daytime, which is consistent with the actual average sound levels of these turbines. Also, most respondents thought the sound is louder in strong winds and when the wind is blowing towards their dwelling, which is consistent with the wind dependent sound power level and the directivity of the sound (higher at the downwind side).
Comparing equal Lden levels of road traffic and wind turbine sound gives no information on the levels or the relative audibility of each sound at specific times. In fact, at equal Lden values wind turbine sound levels will be higher at night than road traffic sound levels because of the different diurnal patterns, the different spectral distributions and the modulation present in wind turbine sound. It can be estimated that the Lden due to modern, tall wind turbines must be 6 dB (diurnal variation) + 8 dB (spectral differences) + 5 dB (amplitude modulation) = 19 dB lower then the Lden due to road traffic in order to obtain equal hourly levels at the least busiest traffic hours at night. If the road is a provincial road and not a very busy motorway, there may be shorter or longer periods of time, especially at night, when no road traffic at all can be heard. In that case the Lden due to that road traffic is in fact irrelevant when determining the audibility of a wind turbine.
It is not clear whether the greater distance of the sound shadow to a source is important in relation to annoyance. An upwind receiver may be in the sound shadow of a road but not in the sound shadow of a wind turbine along that road, but the receiver is in that case also at the front side of the turbine which emits less sound than the rear side.
