IEC Acoustic Standard IEC 61400-11

Recommendations

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7 Measurements and Measurement Positions A-weighted sound pressure level At least 30 1-minute averaged measurements with wind speed when the turbine is operating (AWEA mod:10-sec) At least 3 measurements per wind speed bin. (For statistical purposes/good practice if using 10-second averages then 10 points per wind speed bin) At least 30 minutes of background (turbine not operating) covering the same as turbine measurements A-weighted one-third octave levels At least 3 spectra measured over 1-minute for each integer wind speed and covering centre frequencies of 50Hz-10kHz (same as above modify for 10-second averages) Background covers the same requirements A-weighted narrowband At least 2 minutes closest to the integer wind speed NATIONAL RENEWABLE ENERGY LABORATORY 16
7 Measurements and Measurement Positions Non-acoustic measurements: wind direction Method 1: determination of wind speed from the electric output and the power curve (not covering since not applicable to all small wind turbines) Method 2: determination of wind speed with an anemometer (AWEA mod) Adjust wind speed to 10m height and reference roughness length (covered in section 8) Measurement by anemometer at a height between 10m and hub height Wind speed data collected and arithmetically averaged over the same period as the acoustic measurements NATIONAL RENEWABLE ENERGY LABORATORY 17
Page 1 and 2: Part I Acoustic Testing Stepping Th
Page 3 and 4: 1 Scope General description and pur
Page 5 and 6: 3 Definitions and 4 Symbols and Uni
Page 7 and 8: 6 Instrumentation Required acoustic
Page 9 and 10: 6 Instrumentation Acoustical calibr
Page 11 and 12: 6 Instrumentation Traceable Calibra
Page 13 and 14: 7 Measurements and Measurement Posi
Page 15: 7 Measurements and Measurement Posi
Page 19 and 20: 8 Data Reduction Procedures Wind sp
Page 21 and 22: 8 Data Reduction Procedures Apparen
Page 23 and 24: Look at NoiseLab Setup Calibration
Page 25 and 26: Filtering for Valid Data - Listen f
Page 27 and 28: Binning and Averaging After binning
Page 29 and 30: Background Correction Calculate the
Page 31 and 32: NATIONAL RENEWABLE ENERGY LABORATOR
Page 33 and 34: One-Third Octave Levels Sound press
Page 35 and 36: Tonality To begin - Two minutes of
Page 37 and 38: Determine Critical Bandwidth Calcul
Page 39 and 40: Classify ‘Masking’ A line is cl
Page 41 and 42: Determination of Tone Level The sou
Page 43 and 44: Determination of Masking Level Calc
Page 45 and 46: Determination of Tonality The diffe
Page 47: Tonality can be complicated and the

IEC Acoustic Standard IEC 61400-11

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