The standard calculation methods (ISO9613 or BS5228) calculate LAeq values, whereas ETSU R-97 advises that LA90 should be used as the noise index. However, it also advises that LA90 is about 2 dB below LAeq for a wind turbine. In other words, an acceptable approximation is that:
LA90 = LAeq - 2.
So you can calculate noise contours in terms of LAeq and when you have loaded the contours, in the NoiseMap Contour Display Parameters dialog, all you need to do is to set the 'Offset to Add' value to -2.0, and the resulting contours will be an acceptable approximation to LA90.
There isn't the same function for adding an offset to receiver levels. Instead, we suggest you export them to a spreadsheet and subtract 2 dB in the spreadsheet.
