By Robert W. Rand, ASA, INCE
Rand Acoustics, Boulder
January 29, 2016

Summary

Differential acoustic pressure measurements were acquired and logged at three homes in the vicinity of the Golden West Wind Facility in El Paso County, Colorado during December 2015 and January 2016. A week of data was analyzed for each of the three homes and daily spectrograms produced which are attached. Each day’s data consisted of approximately 4.3 million differential pressure samples with a week comprised of some 30.5 million samples.

Preliminary investigation confirmed the presence of recurring acoustic pressure oscillations at 0.2 to 0.85 Hz (the “blade pass frequency” or BPF) which are associated to the Golden West wind turbine rotations. At times multiple oscillation frequencies were observed, consistent with multiple turbines operating at different rotation rates. Oscillations appeared to be more pronounced when the turbines are more upwind rather than downwind. Neighbors reported they are mostly downwind due to turbine location relative to home location and for the prevailing winds in the region.

Typical BPF total acoustic power were computed for example portions of the differential pressure data sets. Crest factors (the ratio of RMS to peak levels) were also computed for segments dominated by wind turbine rotation and uncontaminated by other noise, with typical crest factors of 13-19 dB. Totalized BPF RMS levels ranged from 56 to 70 dB re 20µPA, with peak levels from 71 to 89 dB. The RMS and peak levels are similar to those found at other sites with appeals to stop the noise, legal action, and homes abandoned.

It is understood from neighbors that they have experienced disturbance since the turbines started operating whereas prior to turbine operation there was no similar disturbance. It is understood that neighbors report improvement when turbines are shut down (not rotating) or when they remove themselves physically away from the Facility a distance of several miles.

El Paso County noise regulations define “Sound” as oscillations in pressure (or other physical parameter) at any frequency, and, prohibits noise disturbance due to acoustic oscillations.

The analysis is far from complete in that numerous segments of each day at each monitoring location could be analyzed and associated to journal entries and/or medical data. The reported association of proximity to the operating facility to disturbance in health and quality of life appears supported by the acoustic data acquired for this preliminary investigation. These preliminary investigations suggest that there is a condition of noise disturbance due to very low frequency acoustic pressure oscillations in the vicinity of the Golden West Wind Facility when it is operating, with more severe impacts downwind.