MAS believe that the best way of ensuring expert consultation and advice is to constantly seek an in depth understanding of the issue(s) in question; where information is lacking, research and investigation is paramount. Too often is acoustics referred to as an inexact science; whilst this is true in some respects it should not be used as an excuse. Outside of day to day consultancy MAS are constantly striving to understand and discuss issues relating to noise from wind development.
Presentation given at the 5th International Conference on Wind Turbine Noise Denver 28-30 August 2013
MAS Environmental presented the following paper at the 5th International Conference on Wind Turbine Noise Denver 28-30 August 2013
Audible amplitude modulation - results of field measurements and investigations compared to psychoacoustical assessment and theoretical research
In the UK the cause of amplitude modulation (AM) and the ability to predict its occurrence is considered abstruse by many. Few have experienced or measured AM and yet conclusions are frequently made asserting that it is rare and that any action to counter its effects is limited by minimal knowledge surrounding its nature and cause. This paper aims to advance current knowledge and opinion of AM. Methods used to successfully investigate AM are confirmed. AM should be measured during evening (after sunset), night time or early morning periods. Meteorological effects, such as atmospheric stability, which lead to downward refraction resulting from changes in the sound speed gradient alter the character and level of AM measured.
AM is generated by all wind turbines including single turbines. Propagation conditions, mostly affected by meteorology, and the occurrence of localised heightened noise zones determine locations that will be affected. Measurements from eleven wind farms have been presented and discussed in relation to current research and theory. Findings confirm that AM occurrence is frequent and can readily be identified in the field by measuring under suitable conditions and using
appropriate equipment and settings. Audible features of AM including frequency content and periodicity vary both within and between wind farms. Noise character can differ considerably within a short time period. The constant change in AM character increases attention and cognitive appraisal and reappraisal, inhibiting acclimatisation to the sound. It is advised that those responsible for approving and enforcing wind energy development improve their understanding of the character and impact of AM. This can be achieved by attending a listening room experience which has been trialled and is discussed in this paper.
Download the paper (pdf)
Download the presentation (pdf)
View the animated graphs (flash)
Other useful papers presented:
Assessment of wind turbine noise in immission areas (pdf)
by Hideki Tachibana Chiba Institute of Technology, Hiroo Yano Chiba Institute of Technology, Akinori Fukushima NEWS Environmental Design Inc.
MAS Study of the article method versus ETSU-R-97
In 2009 an article was published in the Institute of Acoustics magazine 'Acoustics Bulletin'. The article proposed changes to the way wind farm noise was assessed primarily relating to the issue of wind shear. It was not based on research or empirical measurements and was developed following some widely stated assumptions about the effects of wind shear. This paper challenges the assumptions made by the article on the influence of wind shear on wind turbine noise and shows that use of this places the protection of nearby residents amenity at risk, allowing more noise from wind farms than would be applied using the original principles of ETSU-R-97. A brief summary of the results of the study is given below, the full article and summary can be downloaded by clicking on the links at the bottom of this page.
The table below clearly shows that across all wind speeds for both wind shear exponents assessed that there is no gain in adopting the article method. In 72-75% of cases analysed the article method actually resulted in a loss of protection to communities. Looking only at the critical wind speeds of 5-7m/s nearly all cases (91-95%) resulted in a loss of protection to communities by using the article method.