Cooper, S. Measurements at Sonia Trist’s Cape Bridgewater House 89
A series of graphs were presented at the meeting of the Pacific Hydro Community Consultative Committee at Cape Bridgewater on Monday 2nd June, 2014, where independent acoustician Mr Steven Cooper presented the preliminary results of his acoustic investigation work.
This work was commissioned by the wind developer Pacific Hydro, and is being performed in collaboration with three households in Cape Bridgewater where the families have reported serious adverse health impacts for a number of years.
Simultaneous measurements for noise and vibration both inside and outside the houses have been undertaken as part of the detailed acoustic survey, using conventional noise loggers and a more complex recording system.
House 89 turbines operating at 100% power
The first two graphs of interest compare the outside vs inside noise covering the infrasound region to show the typical acoustic signature of operating wind turbines. The peaks are more prominent inside the home. The following two graphs show the presence of an external tone and internal tones across the frequency range normally associated with low frequency noise, at around 24 Hz. The final two graphs show the vertical vibration recorded in a monitor outside the home in the ground, and another vibration recorder located inside the dwelling, on the bedroom floor.
House 89 turbines operating at 10% power
Following the same format for 100% power, the graphs reveal the infrasound and low frequency noise peaks to be more noticeable due to the lower ambient noise. However, the vibration levels are relatively similar.
House 89 turbines shutdown
The graphs represent measurements taken with a wind strength and direction the same as those with 100% power, but with the turbines shut down.
The graph of infrasound inside the home shows NO characteristic wind turbine signature present, in contrast to the infrasound graphs for when the turbines are operating at both 10% and 100% power generation.
The overall levels of infrasound during the shutdown are similar to that when the turbines are operating, but can be described as broadband noise, without the peaks seen particularly in the internal measurements when the turbines are operating. The vibration levels with the turbines not operating are similar to those when the turbines are operating.
Turbine CBW 29 – Vibration measurements
Triaxial vibration measurements were conducted on turbine CBW 29 with the turbine operating, and the turbine stationary, but other turbines nearby operating.
These measurements revealed the presence of distinct tones which have been found in other acoustic survey work at residential properties at other wind developments, but the source of these 23 Hz tones and its second harmonic (46 Hz) was unknown until now.
It was suggested by Mr Cooper that there is a possibility of noise radiating from the tower structures which can still be identified during shutdowns when the wind is blowing. In addition, the presence of this discrete frequency in vibration measurements external to dwellings may suggest there is an issue of groundbourne vibration, subject to further investigations.