Acoustic Engineering Investigation at Cape Bridgewater Wind Facility

Acoustic Engineering Investigation into Airborne and Ground-Borne Pressure Pulses from Pacific Hydro’s Wind Turbines at Cape Bridgewater

Waubra Foundation Definitive Document
1 February, 2015

A Simplified Explanation of the Findings, Previous Research, and the Consequences

1. Background

  • Turbines create “waste energy” in the form of airborne pressure waves (sound) and ground-borne pressure waves (vibration).
  • Noise is that part of the sound frequency spectrum which is audible, but “noise” is also defined by psychoacousticians as “unwanted sound”.
  • The strength (sometimes expressed as a loudness in the case of noise) of the sound is measured in decibels (“dB”).
  • The wavelength of individual sound waves is a measure of the distance between the peaks of the pressure waves. The speed of sound divided by the wavelength gives the frequency of the sound and is expressed in hertz (Hz).
  • Where the frequency of the sound waves is below 20 Hz, the distance between the waves is relatively long, and the general term for this portion of the frequency spectrum is known as infrasound. Infrasound is only audible at very high levels (dB). However it can be damaging to the human body at levels well below audibility.
  • Impulsive infrasound from a variety of industrial sources has long been known to have the potential to be harmful to humans, especially with chronic exposure. For example, human and animal studies have shown infrasound directly causes both physiological stress, and collagen thickening in a variety of tissues including cardiac valves, arteries, and pericardium which themselves lead to a variety of cardiovascular diseases.
  • Infrasound persists for much greater distances than audible sound and, unlike audible sound, penetrates well insulated building structures (including double glazing) with ease; and often increases the impact by resonating within the house, like a drum. This occurs, regardless of the source of sound & vibration energy. Penetration of buildings and amplification via resonance can also occur from sound and vibration from natural sources such as earthquakes and thunder.
  • Standards for wind turbine noise pollution in Australia are set in audible decibels (“dBA”) outside houses. Use of dBA excludes accurate measurement of frequencies below 200 Hz, including both infrasound (0 – 20 Hz) and low frequency noise (20 – 200 Hz). These Standards do not require infrasound (either within or outside homes) to be predicted in planning submissions nor to be measured in the required compliance testing to the planning permit noise conditions. Most jurisdictions do not require wind turbine generated low frequency noise to be predicted or measured either (unlike other sources of industrial noise). In fact most noise measuring instruments and microphones are unable to measure accurately in the infrasound range, especially below 8 Hz., and some Standards explicitly specify the use of equipment which cannot measure infrasound.

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