Acoustic performances of a vertical board for wind turbine noise immission measurements

概要

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In many measurement situations of wind turbine noise immission, the effects of background noise and reflected sound waves from building facades on the measurements are a major problem in addition to the wind-induced noise on the microphone, resulting in a low signal-to-noise ratio of measurements. The use of a vertical board mounted with a microphone was suggested in the document of IEA recommended practices in case of such a problem. Acoustic tests of the board had been carried out on two types of ground to investigate whether performances of the board outdoors are as expected. Results of the tests revealed that one-third octave band measurements were affected by the diffraction of sound waves incident on the board and agreed well with the previous results for a lower to mid frequency range, while the measurements were found to have irregularities as large as ±2dB for higher frequencies. The A-weighted measurements were found to be within +6dB ±0.5dB compared to that of the free-standing microphone. The shielding effect of the board turned out to depend both on the angle of incidence to the board and microphone position and was found to be as large as 10dBA.
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