By William K.G. Palmer, P. Eng.
7th international conference on Wind Turbine Noise – May 2-5, 2017 – Rotterdam
A rigorous and repeatable method is proposed to monitor and assess wind turbine noise. The method had to consider that an effective monitoring system must take into account more than just averaging sound power levels over a long term.
The method recognizes that humans are bothered by the changes and annoying characteristics that occur, as well as long term averages. Others describe this as the need to determine how the special characteristics of sound quality may impact quality of life. To verify this approach, assessments were conducted using the method at two wind power developments.
Use of this rigorous method permitted gathering evidence of the presence of characteristics described as annoying by residents. The evidence produced by this method is clear: the method itself is repeatable and it considers the requirements of a more comprehensive system.
In contrast, compliance methods currently in use have not demonstrated the capability of verifying non-conformance of the same wind power developments, even though in one case the monitoring has been in progress for eight years.
Use of the proposed method will permit others to gather quality evidence in a similar manner.
This paper has demonstrated a method for rigorous monitoring of wind turbine sound. The goal of the method was to establish evidence for the condition noted by Karl D. Kryter: “The most direct, and perhaps most valid, insight into the possible presence and magnitude of stress reactions in general living environments is probably that which has been obtained from attitude surveys and real-life behaviour of people.” Behaviours such as walking away from an unsold loved home to live at the home of a family member, or when normal people become activists in trying to communicate their concerns provide such valid insights. The rigorous method had to consider the present acceptance criterion for wind turbines, in light of the insight given by those who study the quality of noise and its relation to annoyance. Those who study the subject identify that, “Current acceptance criterion relying on sound pressure levels averaged over long time periods and suppressing all aspects of quality cannot identify the specific properties of environmental noise situations.”
A repeatable and transparent method of predicting the expected sound pressure level was presented. A rigorous method of monitoring the actual sound conditions was described. This was used to conduct assessments at two different wind power developments with two different turbine types. Using the method it was possible to generate reproducible evidence of some of the special acoustical properties that are affecting quality of life. Thus it could verify that conditions identified by residents as troublesome do exist, when the current acceptance criterion was unable to detect problems.
The paper outlines a method of preparing reproducible sounds to permit a “jury-test” at the poster session in a repeatable manner of special acoustical qualities such as modulated cyclical sound, or tonality. The demonstration will show evidence that two sounds with the same A-weighting, in the absence of consideration of the special characteristics of the sound, are not equal in annoyance.