IOA publishes AM measurement guide

The Institute of Acoustics has published its preferred method of measuring and rating amplitude modulation (AM) in wind turbine noise.

Known as the Reference Method, it is essentially a development of the Hybrid Reconstruction Method that was described in a discussion document published by the Institute’s Amplitude Modulation Working Group (AMWG) in April 2015.

The recommendation is contained in the working group’s final report, which follows a large-scale public consultation exercise that began with the publication of the discussion document.

The document explains how the metric has been derived, and how it is to be technically implemented to derive a value for the level of AM in a wind farm noise signal.

The Institute will be writing to the Department of Business, Energy and Industrial Strategy to inform it of the IOA metric publication, with a view to encouraging its use in planning conditions designed to control AM.

The AMWG has not addressed the question of what level of AM in wind turbine noise (when measured by a specific metric) may be appropriate. Establishing and setting appropriate levels of AM were outside of the scope of this study, but the proposed metric is intended to assist with further research.

Gavin Irvine, AMWG chairman, said: “The publication of this final report marks an important milestone for the IOA, as we are releasing details of what we believe to be the ideal metric for wind turbine generated amplitude modulation (AM) noise for the very first time. This metric has been extensively tested on real, measured data, from wind farms and elsewhere, and the code is being provided so that all stakeholders involved in controlling noise from wind turbines can understand how the methodology works and evaluate their own data. This should ensure a level playing field in the area of AM, and has the potential to ensure that such noise is better controlled by wind farm operators.”

The report and the consultation responses to the discussion document are available for viewing/downloading in the publications section of the Institute’s website. Click here to access both documents. The code can be accessed by clicking here.