Sound level distributions on a circular ground board for wind turbine noise measurements

摘要

International standard IEC 61400-11 which describes acoustical noise measurement techniques for wind turbines requires a microphone to be mounted on a board placed on the ground. For the purpose of investigating the influences of ground and board size upon one-third octave band sound pressure level and A-weighted sound pressure level measurements, field experiments simulating wind turbine noise measurements were conducted on sod-covered and bare soil surfaces. The results revealed that while the spectrum measurements on the boards were influenced considerably by the acoustical conditions surrounding the board, the A-weighted measurements were found to be not or far less affected. In measurements taken using the board on grass-covered ground, the gaps inevitably created between the board and grass are strongly suspected to have enlarged the spectrum measurement error by enhancing the scattering or diffraction along the edge of the board. These acoustic phenomena involving measurements taken with the board on grass-covered ground likely negated any improvements that might have been expected by use of a larger board. Contrary to this, if the board was placed carefully on the bare soil so as not to create any gaps, the effects of scattering or diffraction on the measurements were reduced considerably and use of a larger board did slightly improve the spectrum measurements. (C) 2002 Institute of Noise Control Engineering. [References: 7]