The issue of an updated noise guideline for wind farms in South Australia represents the third (public) attempt at the Environment Protection Authority (EPA) to address wind turbine noise and unfortunately still contains significant errors and omissions as to to fundamental requirements with respect to the protection of the amenity of residents in proximity to wind farms.
Despite complaints from residents and documentation in relation to such complaints, the EPA have not established appropriate criteria to protect the acoustic amenity of residents. …
The guidelines do not identify what level of noise, or what noise characteristics, will result in sleep disturbance. Assuming that most people will sleep indoors, then Section 2.3 identifies that sleep disturbance is likely to be considered inside as an unreasonable interference that in turn could create an adverse health impact. Section 2.3 is silent on what is a sufficient outdoor amenity to not create an adverse health impact. … There is no information to identify what wind turbine noise levels and characteristics create and adverse impact for hosts or non-hosts. … Without this material provided in the noise guidelines then there is absolutely no way that any environmental assessment can be undertaken for a wind farm and identify that there will be no adverse noise impact. … There is no material to support the limits specified in the guidelines, and in light of no dose-response data for wind turbines, the matter of not identifying the precautionary principal in creating a noise guideline in relation to wind turbines is not acceptable.
In relation to fulfilling the ethical and moral obligations of acousticians to rural communities in proximity to wind farms, research has been conducted by multiple researchers including Professor Colin Hansen, Associate Professor Con Doolan, & Dr Kristy Hansen at Adelaide University & Flinders University, Dr B Thorne, Mr L Huson and the author into what constitutes the acoustic signature of wind turbines and how it is impacting upon people. The Adelaide University researchers conducted almost all of their research at Waterloo Wind Farm in South Australia, and have published a text book as well as multiple peer reviewed published papers. There is no reference to any of that material in the bibliography to the draft guidelines … In addition to the failure of the SA EPA to establish the acoustical basis of the core objectives and how the nominated levels will protect the community for adverse noise or health impacts there a technical issues in the guidelines that question the technical capability of the SA EPA to fulfil their obligations to protect the rural community from adverse noise impacts from wind turbine installations.
There is general agreement in acoustic Standards that there is a distinct different degree of sensitivity to noise by residential receivers during the night to that in the day. There are many Acoustic Standards throughout the world in relation to industrial noise and transportation noise where there is a different weighting (for different acoustic descriptors) applied to noise events that occur in the night-time period when compared to the daytime period. …
The concept for wind turbines of using a generic criteria based upon 24-hour measurements would appear to be inconsistent with general environmental assessments, in that there is an expectation of lower background levels and therefore lower criteria for the night time periods. Background levels at night are typically lower than in the day. Yet the draft guideline does not acknowledge this fact by providing different criteria.
Generally for a wind farm application, with respect to wind data monitoring of the wind for a proposed wind farm is undertaken over a number of years. Therefore, the concept of utilising two weeks of noise data for establishing criteria for a wind farm would appear to be inadequate and not appropriately considered by the EPA.
The difference in prevailing wind for a site or receiver location for the different seasons of the year may be significant in terms of both the assessment of the background level and the predicted noise levels. Such differences are not appropriately reflected in a regression averaging technique based upon hub height wind speeds without any identification of wind direction or seasons.
In the determination of noise criteria for other noise sources such as industry for transportation, the use of dose response curves determines criteria based around 10% of the population seriously or highly affected.
One concept presented in New South Wales by the EPA and Department of Planning is to establish criteria to protect 90% of the population 90% of the time and in that regard ambient background level is expressed in terms of the lowest 10 percentile of the background levels.
It is upon that lowest 10 percentile background level upon which in NSW the background +5 dB(A) limit as a general criterion is based. …
Section 4.7 (Annoying characteristics) repeats the previous errors (in the current and original version of the guideline) in relation to infrasound and clearly an inadequate literature research that indicates that is not a problem.
The suggestion in Section 4.7 that amplitude modulation or low frequency noise is not expected to impact upon receivers during a substantial fraction of the year is incorrect. …
Amplitude modulation by definition is the variation in the level of a carrier frequency where the variation in the level of that carrier frequency (described as modulation) occurs due to a much lower frequency. …
For a wind turbine when one is utilising the correct terminology, amplitude modulation can be related to the output shaft speed of the gearbox (where that tone is the carrier, as a clear and distinct tone) that is modulated at the rate of the blade pass frequency. Depending upon the turbine model the carrier frequency may be at for example, 25.5 Hz, 26 Hz or 31.5 Hz. A narrowband frequency analysis of the signature reveals side bands (to the gearbox output shaft frequency) that clearly satisfy the definition of amplitude modulation [link ].
However, the audible noise associated with the “swish” or “thumping” noise is not amplitude modulation (by definition) but is a “modulation of the sound” as identified in the New Zealand Standard as a special audible characteristic. One would have expected the SA EPA to have understood the difference between amplitude modulation and modulation of the sound.
The use of the dB(A) level cannot, by definition be considered as a single frequency because it is a result of multiple frequencies. The dB(A) level can be seen to be modulated at the rate of the blade pass frequency. Therefore, the modulation (variation) of the dB(A) level cannot be called amplitude modulation. The periodic variation on the amplitude of the dB(A) is a modulation of the dB(A) level, where the modulation occurs at an infrasound rate. …
Additionally, it must be noted that determining “compliance” by use of a L90 average level would not account for the modulation of the acoustic signal. The time signature of a wind turbine identifies a series of pulses which occur at the blade pass frequency. The blade pass frequency is in the order of 0.86 Hz for a three bladed turbine operating at 17 rpm.
Therefore, there are questions as to whether infrasound as a concept of sound itself is generated by wind turbines [link1 ; link2 ]. As such the concept of audibility or effects from infrasound as suggested in the guideline may not be appropriate. The threshold of audibility for a tone is different to that of a pulse, especially in the infrasound region [link]. Research work and investigations undertaken by the author (by testing conducted in a chamber that could produce infrasound pure tones down to 1 Hz) identified that there is a difference in terms of the perception of infrasound for pure infrasound tones on a constant basis versus pulsations. There is also a hysteresis effect in the thresholds (for both sensitivity and hearing) when increasing the level of infrasound versus decreasing the level [link]. Additional work undertaken by the author has identified the provision of signals recorded in houses in proximity to wind farms and specifically using filters to prohibit any sound below 40 Hz into the speakers, to find that digital frequency analysis of the signal will show the presence of a signature in the infrasound region by way of the incorrect analysis of the pulsations, when in fact there is no infrasound present [link ]. …
The suggestion in Section 4.7 of the draft guideline that annoying characteristics are not fundamental to a typical well-maintained wind farm is incorrect. In the UK there have been efforts to define “excessive amplitude modulation” in light of the increase in annoyance that identifies the above SA EPA claim of annoying characteristics is incorrect. Often residents complain that they hear (generally inside the dwelling but also external to the dwelling) on a continuous basis a low frequency noise when the turbines are operating, with the description typically expressed as a plane that never lands.
The development of wind farms in South Australia has resulted in the creation of a new industrial noise source that gives rise to disturbance to rural residents.
With the benefit of hindsight, it is apparent that the guidelines introduced by the South Australian EPA were not based upon actual wind turbine noise but on criteria for other noise sources without identifying the differences between those established noise source sources and wind turbine noise. Over the ensuring period the size of wind turbines has increased and so has the impact. Therefore one questions the relevance of original work on wind turbine noise carried out in Europe on turbines with significantly lower capacity.
From the outset, the South Australian wind farm guidelines had failed to provide material that identifies how the objectives of the guidelines are satisfied, by not identifying what acoustic impacts occur or adverse health impacts that occur as a result of the operation of wind turbines.
On a statistical basis, the number of complaints from communities in proximity to wind turbines is well above the norm and as such cannot be ignored by any regulatory authority if acting to protect the amenity of residents.
The principal issue that the author has experienced in attending residential properties with respect to wind farms is that residents report sleep disturbance. There appears to be a deterioration over time for some people that are impacted. It is noted that not all people are impacted by wind turbines which is compatible with an analogy for seasickness. …
There is often an excuse provided that there are no studies to show that wind farms create health impacts, which can also be said in the reverse case that there are no studies to show there are no health impacts. Because there is a lack of studies.
Work undertaken by the author has identified that in a laboratory situation persons who have become sensitised to wind turbines can detect the presence of a wind turbine signal even though it is inaudible [link ]. I am advised by persons who have been adversely affected by wind turbines to the point of having to relocate from their properties (permanently or regularly) and who have recently participated in testing undertaken by Flinders University that in terms of the sleep study they have experienced disturbed sleep.
Further work by the author in relation to the investigation of fluctuations (that is not just restricted to wind turbine noise) reveals that the presence of excessive modulation, which occurs on a regular basis from wind turbines, gives rise to a greater level of annoyance which should be added to the A-weighted levels with respect to wind turbine noise [link ].
Download original document: “South Australia Wind Farm Guidelines Consultation ”
URL to article: https://www.wind-watch.org/documents/south-australia-wind-farm-guidelines-consultation/
URLs in this post:
 link: https://www.wind-watch.org/documents/simplified-method-for-determination-of-amplitude-modulation-of-audible-and-inaudible-wind-turbine-noise/
 link1: https://www.wind-watch.org/documents/wind-farm-infrasound-are-we-measuring-what-is-actually-there-or-something-else/
 link2: https://www.wind-watch.org/documents/use-of-synthesised-or-actual-wind-turbine-noise-for-subjective-evaluation-purposes/
 link: https://www.wind-watch.org/documents/subjective-perception-of-wind-turbine-noise-the-stereo-approach/
 South Australia Wind Farm Guidelines Consultation: https://docs.wind-watch.org/wind-farm-guidelines-consultation.pdf