Acoustic Field Surveys
Relevant information from field studies/surveys is in three distinct groups. The aim of the acoustic surveys is to find out what dose of sound energy in the different frequencies people are exposed to, and over what distance and how often the adverse effects are occuring, particularly sleep disturbance at night. These then are used to develop “dose – response” curves which are then used for planning and noise pollution regulation purposes.
Recommended levels for infrasound and low frequency noise exposure to prevent community “annoyance” symptoms were established nearly 30 years ago from a major US government funded research initiative, led by Neil Kelley, and involving the cooperation and assistance of a number of American research institutes and universities, including NASA, and MIT.
These recommendations have never been implemented in wind turbine noise pollution regulations anywhere in the world, indeed the regulations have been formulated to exclude measurement of these frequencies, and to exclude internal home measurement. The wind industry and its acousticians have assisted with the development of these regulations.
Rick James, an American acoustician, has taken a keen interest in the history of the reported problems resulting from exposure to infrasound and low frequency noise from a variety of sources – his detailed review article, published in the Bulletin of Science and Technology is attached to Professor Colin Hansen’s submission to the second Australian Federal Senate inquiry in November, 2012.
United States research 1980s downwind bladed single wind turbine
The first relevant acoustic field survey relates to an intensive investigation into the noise impact in about a dozen homes 3km from a single downwind bladed wind turbine in the USA. The field research was commissioned by the US Department of Energy in 1981, to investigate the cause of some unanticipated complaints from the nearby residents. It was conducted with participants from multiple US universities, research institutions such as NASA, and companies such as General Electric.
The results were reported in 1985 – the researchers found the symptoms of annoyance were caused directly by the infrasound and low frequency noise emissions from the turbines which penetrated inside, and resonated within, the building where the residents reported the “annoyance” symptoms. The researchers determined the acoustic exposure levels outside the buildings which they judged were necessary to protect the residents, on the basis of the field data they had collected (from p 225):
“the joint radiation levels (expressed in terms of acoustic intensity and measured external to a structure) in the 8, 16, 31.5 and 63 Hz standard (ISO) octaves should not exceed band intensity threshold limits of 60, 50, 40 and 40 dB (re 1 pWm -2) more than 20% of the time. These figures compare favourably with a summary of low-frequency annoyance situations by Hubbard .”
The field research built on previous work on the perception of noise, sound and vibration energy inside homes by Harvey Hubbard, a researcher with NASA (reference 32 in the quote above) and the field survey findings were consistent with this previous work.
The researchers also specifically acknowledged the problem of sensitisation which they called “conditioning”. They stated the following in section 8.0 at page 199:
“It is clear from our discussion in the previous sections that the only acceptable method of curtailing complaints from residents in the vicinity of an operating MOD-1 turbine is to eliminate, or at least reduce, the impulsive character of the disturbing acoustic radiation to below perceptible levels. The task was made more difficult by the level of conditioning and resulting sensitivity of a few of the families involved, particularly the residents of #2, #7, #8 (and their immediate neighbours).”
This field research published in 1985 was subsequently followed by laboratory research published in 1987, which investigated the impact of different sources of noise, reproduced in a specially constructed building to assess infrasound and low frequency noise with respect to building resonance and annoyance.
The laboratory research results were presented at the 1987 Windpower conference, organised by the American Wind Energy Association, the United States Government Department of Energy, and the Solar Energy Research Institute.
Other research by William Willshire (NASA 1985) found that infrasound from wind turbine emissions was measured 10km from the wind turbine. The bibliography within this document details of much of the research performed over this period of time.
The significance of the body of research by Neil Kelley and his team cannot be overstated. It is the best information we currently have about what levels of infrasound and low frequency noise may be sufficient to protect most of the community from harm. However there are concerns that the new large upwind turbines such as the VESTAS V 90 and V 112’s at Waterloo and Macarthur respectively, may require more protective operating parameters, because of the greater proportion of their sound energy down in the lower frequencies.
Scandinavian research on smaller upwind wind turbines
Numerous research projects in Europe were conducted in the early 2000s, and details of some of the peer reviewed published papers which resulted can be found listed in the Canadian Literature Review by Drs Arra and Lynn.
There is also a useful summary of some of the research by Jim Cummings of Acoustic Ecology in the 2011 (page 42) report on wind turbine noise. Cummings makes the very important point that the data from the individual large European studies shows that rural residents living in quiet background noise environments are more annoyed by the wind turbine noise than those living in more urban noisier environments. Aggregating the data from the studies from different locations hides this effect.
Dr Frits Van Den Berg identified in 2006 that the modern upwind bladed wind turbines also emitted a significant part of their sound energy as infrasound and low frequency noise, even though it was less than the infrasound emissions for downwind bladed turbines such as the MOD-1 wind turbine used in the 1985 Kelley research.
Dr Nina Pierpont critiqued some of the Scandinavian acoustic research with respect to the conclusions drawn about the health and medical problems in these studies in her report for clinicians.
Dr Chris Hanning has also critiqued some of this acoustic research with respect to comments and conclusions about the extent and severity of reported sleep deprivation. At 3.1.2 in his court evidence for the proposed Straboy wind development in Ireland, he states:
“Unfortunately all government and industry sponsored research in this area has used reported awakenings from sleep as an index of the effects of turbine noise and tend to dismiss the subjective symptoms. Because most of the sleep disturbance is not recalled, this approach seriously underestimates the effects of wind turbine noise on sleep.”
Field research from larger upwind bladed turbines
There is emerging field research on larger upwind bladed wind turbines which is providing valuable information about the acoustic exposures impacting on the residents, especially in the infrasound and low frequency noise ranges. There is also old research recently rediscovered, again conducted by Neil Kelley, on upwind bladed wind turbines. Kelley has confirmed that they too produced infrasound and low frequency noise, and would also be capable of inducing the reported annoyance symptoms.
American acoustician Rick James collected some useful acoustic data in 2009 from the Michigan wind project at Ubly in the USA. The data showed that the infrasound synchronised with the blade passage frequency of 1 Hz and sound pressure levels were measured up to 90dB at a distance of approximately 1500 ft, in the infrasonic range.
Professor Salt’s work using animal models has established a threshold of vestibular response in mammals at 60dBG, which is significantly lower than the threshold for auditory rather than perception response which Professor Leventhall and the wind industry have claimed is safe, specifically 85 dbG. Incidentally, this assertion of Professor Leventhall’s was shown to be incorrect by the 1985 US acoustic field research by Kelley et al where people clearly perceived the sound and vibration energy and were annoyed by it well before they could hear it.
James and Bray presented the information from Ubly at the 2011 Noise Conference, and showed that A, C, and G weighting filters discarded the very low frequencies generated by wind turbines and were therefore not appropriate to use. They showed that the bulk of the wind turbine infrasound is below 5 Hz, and as much as 90 % is below 10 Hz. They also showed that averaging techniques will destroy information about the peaks of sound energy, and it is the peaks which people will perceive, sometimes as pulsations. They also discussed how the wind turbine acoustic spectrum is heavily weighted down into the infrasound and low frequency range.
Psychoacoustician Dr Bob Thorne conducted numerous acoustic measurements at wind developments in Australia and New Zealand, as part of a longstanding research program, including the Dean report in July 2010, commissioned by Noel Dean, a resident at Waubra driven out of his home by the effect of the wind turbines on his health. A recent review of the body of work by Thorne includes the most recent case series from two Victorian wind developments which was also submitted to the second Australian Federal Senate inquiry involving wind turbine noise. The results of this case series at two Victorian wind developments confirmed the sleep and adverse mental health effects and impaired quality of life also found in residents living near wind turbine developments by Shepherd et al in New Zealand, and by Nissenbaum et al in Maine and Vinalhaven, USA.
The work in 2010 for Noel Dean at Waubra by Dr Thorne was followed by the Falmouth acoustic field study by Rand and Ambrose, named after the benefactor who funded it, the late Bruce McPherson. Robert Rand and Stephen Ambrose measured the full spectrum inside and outside a home at Falmouth, where the resident had become extremely unwell. They found the acoustic environment inside the home was markedly different to that outside, with a much higher proportion of the sound energy down in the lower frequencies inside, and they specifically mentioned the acoustic resonance issues.
Unbeknownst to Rand and Ambrose at the time, acoustic resonance from wind turbine sound emissions had been studied and measured by Kelley et al nearly thirty years earlier, and found to be the direct cause of the reported symptoms. Unexpectedly Rand and Ambrose both became ill with the characteristic symptoms themselves whilst conducting their measurements.
Steven Cooper, Les Huson and Adelaide University researchers such as Professor Colin Hansen and his research team are some of the Australian acousticians who have been collecting full spectrum acoustic data from the homes of affected residents at locations in New South Wales, Victoria and South Australia, and results will be published when available. The resources section contains some of the work by these acousticians, which includes some of their field data from Australian wind developments.
Professor Con Doolan, Danielle Moreau and Ben Nobbs from Adelaide University, Department of Mechanical Engineering, collected field data down to 10 Hz from a couple of residents living near Waterloo wind development, which clearly showed their annoyance symptoms were directly correlating with the measured low frequency noise at certain doses inside their homes. The results also showed the beginnings of a dose response relationship for those residents. Unfortunately it was not possible to definitively show the noise emissions were coming from the wind turbines, because of the lack of co-operation from the wind developer.
In December 2012, a group of acousticians working in the United States for wind developers and residents together conducted a joint acoustic survey at the Shirley Wisconsin wind project. The four acousticians issued a joint report, as well as individual appendices. The acousticians were Dr Paul Schomer (Dr Schomer’s report is available in the above link), director of Acoustics Standards in the USA, Bruce Walker, George and David Hessler, and Robert Rand (Mr Rand’s report is also available in the above link. The acousticians had almost all worked for both residents and the wind developers previously. The four acousticians made an important statement in their joint report:
“The four investigating firms are of the opinion that enough evidence and hypotheses have been given herein to classify LFN and infrasound as a serious issue, possibly affecting the future of the industry. It should be addressed beyond the present practice of showing that wind turbine levels are magnitudes below the threshold of hearing at low frequencies”
Acoustic impact population survey data
There are three surveys in Australia which have collected useful population data out to between 5 and 10km from wind developments in New South Wales and South Australia, with turbines 2MW and above.
The first was conducted by Adelaide University Master’s student Zhenhua “Frank” Wang, which found that of the households out to 5km from Waterloo wind development, fifty percent of those who responded reported they were moderately to severely impacted by the noise. Mr Wang received his Masters degree from the University, but the research findings were never provided to each of the participants and the thesis has not been made available.
Mary Morris repeated Frank Wang’s survey out to 10km, with similar findings to Mr Wang, but extended out to a greater distance. Waterloo wind developments turbines are VESTAS 3MW V 90 wind turbines.
Patina Schneider collected data from residents living within 10km of the Origin Energy wind development at Cullerin in New South Wales, and found that approximately three quarters of the households who responded had problems with the noise overnight. Cullerin wind development’s turbines are REPOWER 2MW wind turbines.