Setbacks for wind turbines have been established in many jurisdictions to address potential health concerns associated with audible noise. However, in recent years, it has been suggested that infrasound (IS) and low-frequency noise (LFN) could be responsible for the onset of adverse health effects self-reported by some individuals living in proximity to wind turbines, even when audible noise limits are met. The purpose of this paper was to investigate whether current audible noise-based guidelines for wind turbines account for the protection of human health, given the levels of IS and LFN typically produced by wind turbines. New field measurements of indoor IS and outdoor LFN at locations between 400 and 900 m from the nearest turbine, which were previously underrepresented in the scientific literature, are reported and put into context with existing published works. Our analysis showed that indoor IS levels were below auditory threshold levels while LFN levels at distances >500 m were similar to background LFN levels. A clear contribution to LFN due to wind turbine operation (i.e., measured with turbines on in comparison to with turbines off) was noted at a distance of 480 m. However, this corresponded to an increase in overall audible sound measures as reported in dB(A), supporting the hypothesis that controlling audible sound produced by normally operating wind turbines will also control for LFN. Overall, the available data from this and other studies suggest that health-based audible noise wind turbine siting guidelines provide an effective means to evaluate, monitor, and protect potential receptors from audible noise as well as IS and LFN.

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Non-rational uniform B-splines (NURBs) are liberating acoustic design. Geometrical acoustics is no longer limited to flat surfaces. For decades, curved surfaces in computer models had to be broken down into a series of contiguous flat surfaces; a procedure prone to inaccuracy. With NURBs this is no longer the case. A new software tool has been developed by the authors, called NRAT, intended to facilitate acoustic design in NURB based geometries. Two parameters have been developed to quantify the efficiency of reflectors as they are being designed. They are called Reflector Efficiency (RFE) and Receiver Coverage (RCC). The two are quoted together, much like a blood pressure reading might be. The two parameters are required for reasons that became apparent to the authors as the NRAT tool was being developed. A small reflector, perhaps one that might be part of an array, may have a very high percentage of its surface area effectively casting reflections to the audience (perhaps 85%) but those reflections may only cover a small proportion of the audience area (say, 12%). Conversely, a large reflector, for example the side wall of a shoe box shaped concert hall, may only have a small area casting reflections to the audiencein our experience, in the range of 6%. But this small zone efficiently casts reflections across the expanse of the audience, sometimes as much as 90% or more. The quantification of the two RFE/RCC scenarios presented above would be, respectively, "85 over 12" and "6 over 90". Two case studies are presented.

Of interest is the spectral character of wind turbine noise at typical residential set-back distances. In this paper, a spectral statistical analysis has been applied to immission measurements conducted at three locations. This method provides discrete probability density functions for the Turbine ONLY component of the measured noise. This analysis is completed for one-third octave sound levels, at integer wind speeds, and is compared to existing metrics for measuring acoustic comfort as well as previous discussions on low-frequency noise sources.