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Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Acoustic Noise Test Report for 

the Viryd CS8 Wind Turbine

J. Roadman and A. Huskey

National Renewable Energy Laboratory

Technical Report

NREL/TP-5000-58565

July 2013
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Acoustic Noise Test Report for 

the Viryd CS8 Wind Turbine 

J. Roadman and A. Huskey

National Renewable Energy Laboratory

Prepared under Task No. WE11.0206

Technical Report

NREL/TP-5000-58565

July 2013
NOTICE

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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

 Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. 
Viryd IEC Acoustic Noise Report 130319 Page 4 of 51

Acoustic Noise Test Report 

for the

Viryd CS8 Wind Turbine

at the 

National Wind Technology Center 

in Boulder, CO

Conducted for

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

Conducted by

National Wind Technology Center 

National Renewable Energy Laboratory 

15013 Denver West Parkway 

Golden, Colorado 80401

Jason Roadman

Arlinda Huskey

19 March 2013

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 5 of 51

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 6 of 51

Table of Contents

List of Tables ............................................................................................................................................... 6

List of Figures ............................................................................................................................................. 6

1 Background........................................................................................................................................... 8

2 Test Summary....................................................................................................................................... 8

3 Test Turbine Configuration ................................................................................................................. 9

4 Test Site Description.......................................................................................................................... 11

5 Test Equipment................................................................................................................................... 13

5.1 Equipment Descriptions................................................................................................................. 13

5.2 Instrument Locations ..................................................................................................................... 13

6 Results................................................................................................................................................. 14

6.1 Test Conditions.............................................................................................................................. 14

6.2 Standardized Wind Speed Calculation........................................................................................... 14

6.3 Apparent Sound Power Level ........................................................................................................ 15

6.4 One-Third Octave Analysis ........................................................................................................... 17

6.5 Tonality.......................................................................................................................................... 19

6.6 Uncertainty..................................................................................................................................... 35

7 Exceptions........................................................................................................................................... 36

7.1 Exceptions to the Standard............................................................................................................. 36

7.2 Exceptions to the Quality Assurance System ................................................................................ 36

References................................................................................................................................................. 37

Appendix A. Pictures................................................................................................................................ 38

Appendix B. Calibration Sheets .............................................................................................................. 41

List of Tables

Table 1. Test Results Summary................................................................................................................. 8

Table 2. Viryd Wind Turbine General Data ............................................................................................... 9

Table 3. Measured Blade Pitch Angle Relative to the Hub Plate............................................................ 9

Table 4. Sources of Noise Near the Turbine........................................................................................... 12

Table 5. Equipment List for Acoustic Test ............................................................................................. 13

Table 6. Reference Microphone Positions for the Turbine and Background Measurements 

Collected on 05 December 2012........................................................................................................ 14

Table 7. Test Parameters Used in Calculations ..................................................................................... 14

Table 8. Sound Pressure and Power Levels for Standardized Integer Wind Speeds (5 m/s Through 

12 m/s) ................................................................................................................................................. 16

Table 9. One-Third Octave Analysis for Wind Speed Bins 5 Through 8 m/s ...................................... 17

Table 10. One-Third Octave Analysis for Wind Speed Bins 9 Through 12 m/s .................................. 18

Table 11. Tonality Results (In dBA)......................................................................................................... 20

Table 12. Tonality Results (In dBA)......................................................................................................... 20

Table 13. Tonality Results (In dBA)......................................................................................................... 21

Table 14. Tonality Results (In dBA)......................................................................................................... 21

Table 15. Type B Uncertainty Components for Sound Power Levels and Tonality ........................... 35

List of Figures

Figure 1. Viryd CS8 test turbine at the NWTC........................................................................................ 10

Figure 2. Map of the test site.................................................................................................................... 11

Figure 3. Measured and binned sound pressure levels as a function of the standardized wind 

speed ................................................................................................................................................... 15

Figure 4. Sound power levels as a function of the standardized wind speed.................................... 16

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 7 of 51

Figure 5. One-third octave levels ............................................................................................................ 19

Figure 6. Classification of spectral lines for the 1,032 Hz tone (typical in the 5 m/s bin) ................. 22

Figure 7. Classification of spectral lines for the 1,293 Hz tone (typical in the 5 m/s bin) ................. 22

Figure 8. Classification of spectral lines for the 1,041 Hz tone (typical in the 6 m/s bin) ................. 23

Figure 9. Classification of spectral lines for the 1,311 Hz tone (typical in the 6 m/s bin) ................. 23

Figure 10. Classification of spectral lines for the 1,047 Hz tone (typical in the 7 m/s bin) ............... 24

Figure 11. Classification of spectral lines for the 1,173 Hz tone (typical in the 7 m/s bin) ............... 24

Figure 12. Classification of spectral lines for the 1,311 Hz tone (typical in the 7 m/s bin) ............... 25

Figure 13. Classification of spectral lines for the 1,047 Hz tone (typical in the 8 m/s bin) ............... 25

Figure 14. Classification of spectral lines for the 1,170 Hz tone (typical in the 8 m/s bin) ............... 26

Figure 15. Classification of spectral lines for the 1,326 Hz tone (typical in the 8 m/s bin) ............... 26

Figure 16. Classification of spectral lines for the 246 Hz tone (typical in the 9 m/s bin) .................. 27

Figure 17. Classification of spectral lines for the 1,047 Hz tone (typical in the 9 m/s bin) ............... 27

Figure 18. Classification of spectral lines for the 1,173 Hz tone (typical in the 9 m/s bin) ............... 28

Figure 19. Classification of spectral lines for the 1,338 Hz tone (typical in the 9 m/s bin) ............... 28

Figure 20. Classification of spectral lines for the 246 Hz tone (typical in the 10 m/s bin) ................ 29

Figure 21. Classification of spectral lines for the 1,050 Hz tone (typical in the 10 m/s bin) ............. 29

Figure 22. Classification of spectral lines for the 1,170 Hz tone (typical in the 10 m/s bin) ............. 30

Figure 23. Classification of spectral lines for the 1,329 Hz tone (typical in the 10 m/s bin) ............. 30

Figure 24. Classification of spectral lines for the 1,053 Hz tone (typical in the 11 m/s bin) ............. 31

Figure 25. Classification of spectral lines for the 1,173 Hz tone (typical in the 11 m/s bin) ............. 31

Figure 26. Classification of spectral lines for the 1,341 Hz tone (typical in the 11 m/s bin) ............. 32

Figure 27. Classification of spectral lines for the 3,174 Hz tone (typical in the 11 m/s bin) ............. 32

Figure 28. Classification of spectral lines for the 1,044 Hz tone (typical in the 12 m/s bin) ............. 33

Figure 29. Classification of spectral lines for the 1,173 Hz tone (typical in the 12 m/s bin) ............. 33

Figure 30. Classification of spectral lines for the 1,326 Hz tone (typical in the 12 m/s bin) ............. 34

Figure A1. The sound board during the test .......................................................................................... 38

Figure A2. Test turbine, as viewed from the reference microphone position .................................... 39

Figure A3. Test turbine, as viewed from the meteorological mast...................................................... 40

Figure B1. Calibration sheet for the microphone 2406812 ................................................................... 41

Figure B2. Calibration sheet for the sound level meter........................................................................ 42

Figure B3. Calibration sheet for the acoustic calibrator....................................................................... 43

Figure B4. Calibration sheet for the primary anemometer................................................................... 44

Figure B5. Page 1 of the power transducer calibration sheet.............................................................. 45

Figure B6. Calibration sheet for the pressure transducer.................................................................... 46

Figure B7. Calibration sheet for the temperature sensor..................................................................... 47

Figure B8. Calibration sheet for the wind vane ..................................................................................... 48

Figure B9. Calibration sheet for the 9205 signal conditioning module 14DA726............................... 49

Figure B10. Calibration sheet for the 9217 signal conditioning module 12BFEE2 ............................ 50

Figure B11. Calibration sheet for the 9229 signal conditioning module 12A2037 ............................. 51

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 8 of 51

1 Background

This test was conducted as part of the U.S. Department of Energy’s (DOE) Independent Testing 

project. This project was established to help reduce the barriers of wind energy expansion by 

providing independent testing results for small turbines. Several turbines were selected for 

testing at the National Renewable Energy Laboratory’s (NREL) National Wind Technology 

Center (NWTC) as a part of the Small Wind Turbine Independent Testing project. Acoustic 

noise testing is one of up to five tests that may be performed on the turbines. Other tests include 

duration, safety and function, power performance, and power quality. Viryd Technologies, Inc. 

of Austin, Texas, was the recipient of the DOE grant and provided the turbine for testing.

The primary goal of this test was to characterize the acoustic emissions of the Viryd CS8 wind 

turbine in accordance with the International Electrotechnical Commission’s (IEC) standard, 

Wind Turbine Generator Systems - Part 11: Acoustic Noise Measurement Techniques, IEC 

61400-11, Edition 2.1, 2006-11; hereafter referred to as the “Standard.” This test report 

documents the measurement techniques, turbine configuration, test site, test equipment, and 

results for the following quantities at integer wind speeds from 5 to 12 m/s:

• Apparent sound power level 

• One-third octave band levels 

• Tonality. 

Engineers at the NWTC conducted this test in accordance with its quality system procedures to 

ensure that this final test report meets the full requirements accreditation by A2LA. NREL’s 

quality system requires that the test meet all applicable requirements specified by A2LA and 

ISO/IEC 17025 (or to note any exceptions in the test report). 

2 Test Summary

The turbine was tested in accordance with the Standard. Turbine acoustic emissions and 

meteorological data were collected on 05 December 2012. Standardized wind speed (at 10 

meters) was derived from wind speed measured at hub height (24.9 m). Table 1 gives a summary 

of the test results.

Table 1. Test Results Summary

Standardized wind speed at 10 m height, Vs [m/s] 5 6 7 8 9 10 11 12

Electrical power output calculated from power curve 0.0 0.4 1.8 3.3 4.8 5.8 6.5 6.3

Measured pitch angle [°] Fixed Fixed Fixed Fixed Fixed Fixed Fixed Fixed

Apparent sound power level [dBA] 89.8 90.0 91.5 93.3 94.2 94.5 94.8 95.6

Combined uncertainty in the sound power level, UC 1.0 1.2 1.5 1.2 1.1 1.0 0.9 1.0

Frequency of the most prevalent tone [Hz] 1,03 1,04 1,04 1,04 1,04 1,05 1,05 1,04

Tonality, ΔLk [dBA] 0.62 3.41 5.86 7.00 6.78 6.69 5.80 5.63

Tonal audibility, ΔLa,k [dBA] 3.46 6.26 8.72 9.87 9.64 9.55 8.67 8.49

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 9 of 51

3 Test Turbine Configuration 

Table 2 lists the configuration of the Viryd turbine that was tested at the NWTC. During 

commissioning, small shims were inserted between the hub plate and the blade root, thereby 

pitching the leading edge of the blades into the wind. The pitch angle of each blade with respect 

to the hub plate is fixed. It was measured and is given in Table 3. 

Table 2. Viryd Wind Turbine General Data

Turbine manufacturer and address Viryd Technologies, Inc.

9701 Metric Blvd, Suite 200

Austin, TX 78758

Model Viryd CS8

Rated power (kW) 8

Rated wind speed (m/s) 10

Serial number CS008100X

Blade make, type, serial number Viryd proprietary design, 

011247-029, 011247-030, 011247-031

Generator make, type, serial number Marathon, AC induction, I217, 

215TBFW7027DD L 

Gearbox make, type, serial number Boston Gear, 662B-16L-VIR, Helical Gear, 

594189

Control software Proprietary – PCB

Wind turbine type Horizontal axis, Upwind

Tower type Guyed Lattice

Number of blades 3

Hub height (m) 25.0*

Rotor diameter (m) 8.5*

Horizontal distance from rotor center to tower axis (m) 0.66 m

Speed control Passive stall

Constant or variable speed Constant

Rotational speed at standardized integer wind speed 

from 6 to 10 m/s (rpm)

119-122

Pitch angle at standardized integer wind speeds from 6 

to 10 m/s 

Fixed, see Table 3 

Rotor control devices none

*Measurements verified the rotor diameter and hub height.

Table 3. Measured Blade Pitch Angle Relative to the Hub Plate

Blade Pitch Angle

1 1.4°

2 1.1°

3 1.4°

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 10 of 51

Figure 1. Viryd CS8 test turbine at the NWTC 

(Photo by Mark Murphy, NREL 22258) 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 11 of 51

4 Test Site Description

The Viryd CS8 wind turbine is located at test site 3.3 of the NWTC, approximately 8 km south 

of Boulder, Colorado. The site consists of mostly flat terrain with short vegetation (see Appendix 

A for photos) and has prevailing winds bearing 292° relative to true north. Figure 2 shows the 

turbine and meteorological tower locations, as well as nearby obstructions. NREL limited 

assessments of power and energy production to data obtained when winds were within the 

measurement sector of 211° to 38°. In this measurement sector, the influence of terrain and 

obstructions on the anemometer is small and meets the requirements in accordance with IEC 

61400-12-1 without conducting a site calibration test.

Table 4 lists the nearby turbines and whether or not they were operating during data collection. 

Figure 2. Map of the test site

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 12 of 51

Table 4. Sources of Noise Near the Turbine 

Source Location Shutdown for Noise Test

DOE 1.5 4.0 Yes

Alstom ECO100 3.0 MW 4.1 Yes

CART-3 4.3 Yes

CART-2 4.3 Yes

Siemens 2.3MW 4.4 Yes

Southwest Windpower 

Skystream (two turbines)

3.2 Yes

NW100 1.2 No

Test shed heating, 

ventilating, and air 

conditioning (HVACs) 

3.1, 3.2, 3.3 Yes

Building A60 Hydraulics Industrial 

User Facility 

Yes

Southwest Windpower 

Whisper (two turbines)

1E.2 No

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 13 of 51

5 Test Equipment 

5.1 Equipment Descriptions

Table 5 shows the list of equipment used for the test. All instruments meet the requirements 

defined by the Standard. 

Table 5. Equipment List for Acoustic Test

Instrument Manufacturer Model Number Serial 

Number

Calibration

Due Date

Digital recorder and 

signal analyzer 

Delta Acoustics NoiseLab 1283B54 19 Dec 2013

Microphone Bruel & Kjaer 4189 2406812 18 Dec 2013

Preamplifier Bruel & Kjaer 2671 2373722 18 Dec 2013

Calibrator Bruel & Kjaer 4231 2388951 19 Dec 2012

Anemometer Thies First Class 0609006 17 Sep 2013

Wind vane Met One 020C W5515 17 Sep 2013

Pressure sensor Vaisala PTB101B C10400014 13 Feb 2013

Temperature sensor Met One T200A 0603-1 17 Sep 2013

Power transducer Secondwind Phaser-5-485-

4A20

01091 15 Sep 2013

Data acquisition National 

Instruments

CompactDAQw

/LabView

cDAQ-9172

NI 9229

NI 9217

NI 9205

0x1339A69

12A2037

12BFEE2

14DA726

NA

27 Jun 2013

27 June 2013

27 June 2013

5.2 Instrument Locations

The primary anemometer on the meteorological tower was used to derive the standardized wind 

speed. This tower was located 22.9 meters (m) from the test turbine, at a bearing of 283o true, 

with the top-mounted anemometer at a height of 24.9 m. The wind vane was mounted at a height 

of 23.0 m on the meteorological tower on a cross boom that was approximately perpendicular to 

the predominant wind direction. The turbine was 2.9 rotor diameters from the meteorological 

tower, within the range of 2 and 4 rotor diameters specified in the Standard. 

Table 6 provides the location of the microphone for the measurement sessions.

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 14 of 51

Table 6. Reference Microphone Positions for the Turbine and Background Measurements 

Collected on 05 December 2012

Recording

Distance

Turbine

[m]

Slant

Distance

[m]

Position Relative

to Turbine

[deg true]

Recording 1−7 29.2 39.0 115

Recording 8 29.2 39.0 95

6 Results

6.1 Test Conditions

The analysis was done using the measured wind speed and 10-second averages of the data.

NREL engineers have found that using 10-second averages instead of 1-minute averages better 

characterizes the dynamic nature of small turbines. The range of standardized wind speeds and 

wind directions used for the analysis were 3.3 to 15.1 m/s and 260 to 310 degrees, respectively. 

The range of temperature and pressure were 12.7°C to 18.8°C and 80.7 kPa to 80.9 kPa, 

respectively.

6.2 Standardized Wind Speed Calculation

Standardized wind speed, Vs, was calculated according to Equation 1 and the values in Table 7, 

where Vz is the measured wind speed. 





























































































=

0 0

0 0

lnln

lnln

z

z

z

H

z

H

z

z

VV

ref

ref

ref

zs (1)

Table 7. Test Parameters Used in Calculations

Parameter Name Value

Hub height, (m) H 25.0

Roughness length, (m) zo 0.05

Anemometer height, (m) z 24.9

Reference roughness length, (m) zoref 0.05

Reference height, (m) zref 10.00

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 15 of 51

6.3 Apparent Sound Power Level

Sound pressure levels were binned by wind speed. Sound pressure levels at integer wind speed 

values were calculated using interpolation between bin averages and extrapolation at the ends. 

The sound pressure levels were then background corrected according to the Standard. Figure 3

shows the scatter plot of the sound pressure levels of the validated total (operating plus 

background) and background noise along with the binned sound pressure levels. The measured 

and background corrected apparent sound pressure level at standardized wind speeds of 5 

through 12 m/s are shown in Table 8 along with the calculated sound power levels. Figure 4

shows sound power levels graphed against standardized wind speed. 

Figure 3. Measured and binned sound pressure levels as a function of the standardized 

wind speed

38

40

42

44

46

48

50

52

54

56

58

60

62

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Sound Pressure Level [dBA]

Standardized Wind Speed, Vs [m/s]

Measured Sound Pressure Level vs. Wind Speed

05 Dec 2012 Total

05 Dec 2012 Background

Binned, BG Corrected Total Noise

Binned Total

Binned Background

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National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 16 of 51

Table 8. Sound Pressure and Power Levels for Standardized Integer Wind Speeds 

(5 m/s Through 12 m/s) 

Figure 4. Sound power levels as a function of the standardized wind speed

88

90

92

94

96

98

4 5 6 7 8 9 10 11 12 13

Sound Power Level, LWA [dBA]

Standardized Wind Speed, Vs [m/s]

Wind

Speed 

Bin 

[m/s]

Total 

Sound 

Pressure 

Level

[dBA)]

Background 

Sound 

Pressure Level

[dBA]

Background 

Corrected 

Sound 

Pressure Level 

[dBA]

Sound

Power 

Level

[dBA]

Type A 

Uncert. 

[dBA]

Type B 

Uncert. 

[dBA]

Combined 

Uncert. 

[dBA]

5 53.3 41.5 53.0 89.8 0.7 0.7 1.0

6 53.6 42.4 53.2 90.0 0.9 0.7 1.2

7 55.0 43.1 54.7 91.5 1.3 0.7 1.5

8 56.7 44.1 56.5 93.3 0.9 0.7 1.2

9 57.7 45.1 57.4 94.2 0.8 0.7 1.1

10 58.0 46.5 57.7 94.5 0.8 0.7 1.0

11 58.4 48.1 58.0 94.8 0.6 0.7 0.9

12 59.3 49.4 58.8 95.6 0.6 0.8 1.0

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 17 of 51

6.4 One-Third Octave Analysis

One-third octave levels were analyzed at standardized wind speeds of 5 through 12 m/s. The 

results (with uncertainty) are provided in Table 9, Table 10, and Figure 5. 

Table 9. One-Third Octave Analysis for Wind Speed Bins 5 Through 8 m/s

Center 

Frequency

5 m/s OneThird Octave 

Levels

6 m/s OneThird Octave 

Levels

7 m/s OneThird Octave 

Levels

8 m/s OneThird Octave 

Levels

[Hz] [dBA] [dBA] [dBA]

50 NR NR NR NR 

63 NR NR NR NR 

80 26.7* ± 2.0 26.4* ± 2.0 NR 26.6* ± 2.0

100 29.0* ± 2.0 30.4* ± 2.0 31.4* ± 2.0 32.6* ± 2.0

125 37.4 ± 1.9 39.8 ± 1.9 42.0 ± 1.8 43.4 ± 1.8

160 33.5* ± 2.0 33.3* ± 2.0 32.9* ± 2.0 34.4* ± 2.0

200 40.0 ± 1.9 39.7 ± 1.9 39.0* ± 2.0 38.9* ± 2.0

250 41.5 ± 1.8 41.6 ± 1.8 42.3 ± 1.8 43.9 ± 1.8

315 37.6 ± 1.9 36.6 ± 1.9 36.7* ± 2.0 39.0 ± 2.0

400 41.4 ± 1.9 39.4 ± 1.9 39.1 ± 1.9 40.8 ± 1.9

500 42.1 ± 2.0 39.1 ± 1.8 39.4 ± 1.8 41.6 ± 1.9

630 41.3 ± 1.8 40.4 ± 1.8 41.4 ± 1.8 43.2 ± 1.8

800 40.6 ± 1.8 40.5 ± 1.8 41.2 ± 1.8 42.3 ± 1.8

1,000 45.6 ± 1.8 48.3 ± 1.9 51.6 ± 1.9 53.9 ± 1.8

1,250 44.0 ± 1.8 44.6 ± 1.8 45.3 ± 1.8 46.9 ± 1.8

1,600 40.9 ± 1.8 40.1 ± 1.8 38.7 ± 1.8 38.8 ± 1.8

2,000 40.1 ± 1.8 39.0 ± 1.8 37.5 ± 1.8 37.5 ± 1.8

2,500 39.1 ± 1.8 38.5 ± 1.8 37.9 ± 1.8 37.8 ± 1.8

3,150 37.6 ± 1.8 37.5 ± 1.8 37.3 ± 1.8 37.4 ± 1.8

4,000 34.9 ± 1.8 34.4 ± 1.8 34.0 ± 1.8 33.6 ± 1.8

5,000 27.6* ± 2.0 27.1* ± 2.0 26.9* ± 2.0 27.0* ± 2.0

6,300 NR NR NR NR 

8,000 NR NR NR NR 

10,000 NR NR NR NR 

* The difference between total and background noise was less than 6 dB but greater than 3 dB. A 

standard background correction of 1.3 dB was applied per Section 8.2 of the Standard.

NR The difference between total and background noise was less than 3 dB. According to Section 8.2 

of the Standard, the wind turbine noise was less than the background noise. 

This report is available at no cost from the 

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Viryd IEC Acoustic Noise Report 130319 Page 18 of 51

Table 10. One-Third Octave Analysis for Wind Speed Bins 9 Through 12 m/s

Center 

Frequency

9 m/s OneThird Octave 

Levels

10 m/s OneThird Octave 

Levels

11 m/s OneThird Octave 

Levels

12 m/s OneThird Octave 

Levels

[Hz] [dBA] [dBA] [dBA] [dBA]

50 NR NR 22.4* ± 2.1 25.0* ± 2.1

63 NR NR NR 29.8* ± 2.0

80 NR 28.0* ± 2.0 29.6* ± 2.1 32.7* ± 2.1

100 33.5* ± 2.0 34.5 ± 1.9 34.6* ± 2.0 36.0* ± 2.0

125 44.4 ± 1.8 45.1 ± 1.8 44.5 ± 1.8 43.1 ± 1.9

160 35.6* ± 2.0 37.9* ± 2.0 39.4* ± 2.0 41.1* ± 2.1

200 40.0* ± 2.0 40.4* ± 2.0 41.8* ± 2.0 43.1* ± 2.0

250 45.3 ± 1.8 46.4 ± 1.8 46.0 ± 1.8 45.7 ± 1.9

315 41.3 ± 1.9 42.5 ± 1.9 43.1 ± 1.9 44.6 ± 1.9

400 42.4 ± 1.9 43.3 ± 1.9 43.7 ± 1.9 45.0 ± 1.9

500 43.1 ± 1.8 44.0 ± 1.8 44.3 ± 1.9 45.5 ± 1.9

630 44.4 ± 1.8 45.3 ± 1.8 46.1 ± 1.8 47.2 ± 1.8

800 43.4 ± 1.8 44.4 ± 1.8 45.6 ± 1.9 47.1 ± 1.9

1,000 54.7 ± 1.8 54.2 ± 1.8 54.3 ± 1.8 55.3 ± 1.8

1,250 48.0 ± 1.8 48.6 ± 1.8 48.9 ± 1.8 48.8 ± 1.8

1,600 39.9 ± 1.8 41.1 ± 1.8 42.3 ± 1.9 43.8 ± 1.9

2,000 38.3 ± 1.8 39.2 ± 1.8 40.2 ± 1.9 41.6 ± 1.9

2,500 38.0 ± 1.8 38.5 ± 1.8 39.0 ± 1.8 40.3 ± 1.9

3,150 37.7 ± 1.8 38.1 ± 1.8 38.6 ± 1.8 39.1 ± 1.9

4,000 33.5 ± 1.8 33.7 ± 1.9 34.2 ± 1.9 34.6 ± 2.0

5,000 27.3* ± 2.0 NR NR NR 

6,300 NR NR NR NR 

8,000 NR NR NR NR 

10,000 NR NR NR NR 

* The difference between total and background noise was less than 6 dB but greater than 3 dB. A 

standard background correction of 1.3 dB was applied per Section 8.2 of the Standard.

NR The difference between total and background noise was less than 3 dB. According to Section 8.2 

of the Standard, the wind turbine noise was less than the background noise. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 19 of 51

Figure 5. One-third octave levels

6.5 Tonality

The tonality analysis resulted in reportable tones for wind speed bins 5 through 12 m/s, detailed 

in Table 11 through Table 14. Figure 6 through Figure 30 show 10-second energy averaged 

spectra indicating the classification of spectral lines for each of the identified tones.

0

10

20

30

40

50

60

506380

100125160200250315400500630800

1000125016002000250031504000500063008000

10000

Sound Pressure Level [dBA]

Frequency [Hz]

5 m/s

6 m/s

7 m/s

8 m/s

9 m/s

10 m/s

11 m/s

12 m/s

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Viryd IEC Acoustic Noise Report 130319 Page 20 of 51

Table 11. Tonality Results (In dBA)

Wind speed: 5 m/s 6 m/s 7 m/s

f [Hz] 1,032 1,293 1,041 1,311 1,047 1,173 1,311

∆Ltn,1 3.14 -0.89 9.07 -3.35 4.01 -1.72 -6.60

∆Ltn,2 -0.99 -2.93 -0.03 -0.62 7.40 3.61 -9.21

∆Ltn,3 3.83 0.55 1.95 3.75 8.23 2.91 -8.74

∆Ltn,4 -1.84 -0.34 2.96 3.43 1.32 1.81 -9.55

∆Ltn,5 2.67 -1.90 4.16 1.71 7.29 -1.25 -6.80

∆Ltn,6 -2.68 3.33 2.99 1.17 6.34 -16.02 -16.43

∆Ltn,7 -2.70 -8.65 3.19 -3.87 8.49 3.74 -12.74

∆Ltn,8 -0.34 -4.49 1.04 1.73 4.96 2.69 -16.43

∆Ltn,9 1.75 -3.98 4.18 2.80 2.44 2.41 -12.14

∆Ltn,10 0.78 -0.57 1.12 -1.94 4.73 3.97 -16.43

∆Ltn,11 -5.23 0.20 -0.02 -0.25 4.96 -0.20 -11.24

∆Ltn,12 0.24 -5.42 -0.67 0.72 4.06 1.43 -9.68

∆Lk 0.62 -1.11 3.41 1.04 5.86 -1.91 1.77

∆La,k 3.46 1.96 6.26 4.12 8.72 1.06 4.85

UA 2.9 3.4 3.3 2.5 2.8 2.5 2.9

UB 1.8 1.8 1.8 1.8 1.8 1.8 1.8

UC 3.4 3.8 3.8 3.0 3.3 3.1 3.4

Table 12. Tonality Results (In dBA)

Wind speed: 8 m/s 9 m/s

f [Hz] 1,047 1,170 1,326 246 1,047 1,173 1,338

∆Ltn,1 5.88 4.11 2.04 0.14 6.08 0.76 -4.39

∆Ltn,2 5.37 0.66 1.06 -0.03 4.30 -0.43 -3.91

∆Ltn,3 9.26 -16.02 -0.76 -13.55 8.09 -16.02 -0.09

∆Ltn,4 6.37 -1.63 -16.43 -1.58 7.11 3.25 1.43

∆Ltn,5 9.72 4.08 -0.01 -13.55 5.85 1.67 -0.47

∆Ltn,6 6.82 -2.27 2.37 -1.17 8.82 2.08 -0.53

∆Ltn,7 5.79 0.25 -0.14 -13.55 5.75 0.12 -3.62

∆Ltn,8 7.07 2.79 1.00 -13.55 5.77 1.31 1.05

∆Ltn,9 6.11 3.21 0.91 -13.55 6.64 -16.02 -0.20

∆Ltn,10 6.04 -3.43 -2.26 -13.55 7.63 1.61 2.36

∆Ltn,11 7.29 -0.05 3.95 -13.55 7.11 -16.02 0.02

∆Ltn,12 5.54 -0.86 1.39 -1.35 6.26 1.72 -1.83

∆Lk 7.00 0.95 0.78 -4.23 6.78 0.24 -0.39

∆La,k 9.87 3.92 3.87 -2.17 9.64 3.21 2.70

UA 1.9 3.1 2.2 0.9 1.2 1.2 2.1

UB 1.8 1.8 1.8 2.0 1.8 1.8 1.8

UC 2.6 3.6 2.8 2.2 2.1 2.1 2.7

This report is available at no cost from the 

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at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 21 of 51

Table 13. Tonality Results (In dBA)

Wind speed: 10 m/s 11 m/s

f [Hz] 246 1,050 1,170 1,329 1,053 1,173 1,341 3,174

∆Ltn,1 1.03 5.36 0.56 -4.13 4.13 1.99 -0.73 -4.86

∆Ltn,2 -0.43 7.67 2.15 -0.84 7.71 0.90 -7.89 -8.01

∆Ltn,3 -1.58 5.37 0.79 -0.97 6.30 0.13 -4.11 -7.06

∆Ltn,4 -2.65 8.37 2.73 -1.31 4.89 2.40 -1.52 -4.01

∆Ltn,5 -4.09 6.63 -0.62 -4.14 3.69 3.26 -0.15 -12.12

∆Ltn,6 -1.76 2.78 -2.01 -3.43 6.32 2.12 -0.88 -9.23

∆Ltn,7 -1.42 7.04 1.38 -2.60 4.53 -0.34 -2.93 -9.16

∆Ltn,8 -0.15 5.85 1.49 0.35 6.98 1.96 -5.87 -4.09

∆Ltn,9 -4.31 4.81 0.85 -1.67 5.07 -0.12 -2.97 -6.92

∆Ltn,10 -3.06 8.28 1.69 -6.24 6.22 1.21 -3.45 -20.54

∆Ltn,11 -0.32 7.61 1.54 -4.07 6.61 2.82 0.45 -5.33

∆Ltn,12 0.51 7.34 3.61 0.74 5.27 2.58 -0.14 -3.57

∆Lk -1.21 6.69 1.39 -1.92 5.80 1.72 -1.93 -6.45

∆La,k 0.85 9.55 4.37 1.18 8.67 4.69 1.16 -2.45

UA 1.8 1.9 1.6 2.3 1.1 1.2 2.6 2.9

UB 1.9 1.8 1.8 1.8 1.8 1.8 1.8 1.9

UC 2.6 2.6 2.4 2.9 2.1 2.1 3.2 3.5

Table 14. Tonality Results (In dBA)

Wind speed: 12 m/s

f [Hz] 1,044 1,173 1,326

∆Ltn,1 4.70 -0.43 -0.48

∆Ltn,2 3.42 -15.23 -7.55

∆Ltn,3 4.70 -3.89 -16.02

∆Ltn,4 5.62 -1.58 -16.02

∆Ltn,5 6.54 -2.64 -2.07

∆Ltn,6 6.10 -1.06 -6.91

∆Ltn,7 7.08 -15.23 -16.02

∆Ltn,8 6.19 3.35 -16.02

∆Ltn,9 5.69 0.93 -4.50

∆Ltn,10 5.41 -1.00 -4.13

∆Ltn,11 5.09 -0.71 -5.95

∆Ltn,12 5.86 -1.04 -6.04

∆Lk 5.63 -1.14 -5.70

∆La,k 8.49 1.83 -2.61

UA 1.1 1.4 2.5

UB 1.8 1.8 1.8

UC 2.1 2.3 3.1

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 22 of 51

Figure 6. Classification of spectral lines for the 1,032 Hz tone (typical in the 5 m/s bin) 

Figure 7. Classification of spectral lines for the 1,293 Hz tone (typical in the 5 m/s bin) 

0

10

20

30

40

50

60

951957963969975981987993999

1005

101110171023102910351041104710531059106510711077108310891095110111071113

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

0

10

20

30

40

50

60

11941203121212211230123912481257126612751284129313021311132013291338134713561365137413831392

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 23 of 51

Figure 8. Classification of spectral lines for the 1,041 Hz tone (typical in the 6 m/s bin) 

Figure 9. Classification of spectral lines for the 1,311 Hz tone (typical in the 6 m/s bin) 

0

10

20

30

40

50

60

960966972978984990996

1002100810141020

102610321038

10441050105610621068107410801086109210981104111011161122

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

5

10

15

20

25

30

35

40

45

50

12121221123012391248125712661275128412931302131113201329133813471356136513741383139214011410

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 24 of 51

Figure 10. Classification of spectral lines for the 1,047 Hz tone (typical in the 7 m/s bin) 

Figure 11. Classification of spectral lines for the 1,173 Hz tone (typical in the 7 m/s bin) 

0

10

20

30

40

50

60

70

966972978984990996

100210081014102010261032103810441050105610621068

107410801086

1092109811041110111611221128

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

10

20

30

40

50

60

1083108910951101110711131119112511311137114311491155116111671173117911851191119712031209121512211227123312391245125112571263

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 25 of 51

Figure 12. Classification of spectral lines for the 1,311 Hz tone (typical in the 7 m/s bin) 

Figure 13. Classification of spectral lines for the 1,047 Hz tone (typical in the 8 m/s bin) 

0

5

10

15

20

25

30

35

40

45

50

121212211230123912481257126612751284129313021311

1320132913381347

1356136513741383139214011410

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

0

10

20

30

40

50

60

70

966972978984990996

1002100810141020102610321038104410501056106210681074108010861092109811041110111611221128

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 26 of 51

Figure 14. Classification of spectral lines for the 1,170 Hz tone (typical in the 8 m/s bin) 

Figure 15. Classification of spectral lines for the 1,326 Hz tone (typical in the 8 m/s bin) 

0

10

20

30

40

50

60

1080108610921098110411101116112211281134114011461152115811641170117611821188119412001206121212181224123012361242124812541260

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

0

5

10

15

20

25

30

35

40

45

50

12271236124512541263127212811290129913081317132613351344135313621371138013891398140714161425

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 27 of 51

Figure 16. Classification of spectral lines for the 246 Hz tone (typical in the 9 m/s bin) 

Figure 17. Classification of spectral lines for the 1,047 Hz tone (typical in the 9 m/s bin) 

0

5

10

15

20

25

30

35

40

45

50

195 201 207 213 219 225 231 237 243 249 255 261 267 273 279 285 291 297

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

10

20

30

40

50

60

70

966

972978

984990996

1002100810141020102610321038104410501056106210681074108010861092109811041110111611221128

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 28 of 51

Figure 18. Classification of spectral lines for the 1,173 Hz tone (typical in the 9 m/s bin) 

Figure 19. Classification of spectral lines for the 1,338 Hz tone (typical in the 9 m/s bin) 

0

10

20

30

40

50

60

1083108910951101110711131119112511311137114311491155116111671173117911851191119712031209121512211227123312391245125112571263

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

5

10

15

20

25

30

35

40

45

50

12361245125412631272128112901299130813171326133513441353136213711380138913981407141614251434

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 29 of 51

Figure 20. Classification of spectral lines for the 246 Hz tone (typical in the 10 m/s bin) 

Figure 21. Classification of spectral lines for the 1,050 Hz tone (typical in the 10 m/s bin) 

0

5

10

15

20

25

30

35

40

45

50

195 201 207 213 219 225 231 237 243 249 255 261 267 273 279 285 291 297

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

10

20

30

40

50

60

70

966972978984990996

10021008101410201026103210381044105010561062106810741080108610921098110411101116112211281134

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 30 of 51

Figure 22. Classification of spectral lines for the 1,170 Hz tone (typical in the 10 m/s bin) 

Figure 23. Classification of spectral lines for the 1,329 Hz tone (typical in the 10 m/s bin) 

0

10

20

30

40

50

60

1080108610921098110411101116112211281134114011461152115811641170117611821188119412001206121212181224123012361242124812541260

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

0

5

10

15

20

25

30

35

40

45

50

12301239124812571266127512841293130213111320132913381347135613651374138313921401141014191428

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 31 of 51

Figure 24. Classification of spectral lines for the 1,053 Hz tone (typical in the 11 m/s bin) 

Figure 25. Classification of spectral lines for the 1,173 Hz tone (typical in the 11 m/s bin) 

0

10

20

30

40

50

60

70

969975981987

993999

10051011101710231029103510411047105310591065107110771083108910951101110711131119112511311137

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

10

20

30

40

50

60

1083108910951101110711131119112511311137114311491155116111671173117911851191119712031209121512211227123312391245125112571263

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 32 of 51

Figure 26. Classification of spectral lines for the 1,341 Hz tone (typical in the 11 m/s bin) 

Figure 27. Classification of spectral lines for the 3,174 Hz tone (typical in the 11 m/s bin) 

0

5

10

15

20

25

30

35

40

45

50

12391248125712661275128412931302131113201329133813471356136513741383139214011410141914281437

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

5

10

15

20

25

30

35

40

29192937295529732991300930273045306330813099311731353153317131893207322532433261327932973315333333513369338734053423

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 33 of 51

Figure 28. Classification of spectral lines for the 1,044 Hz tone (typical in the 12 m/s bin) 

Figure 29. Classification of spectral lines for the 1,173 Hz tone (typical in the 12 m/s bin) 

0

10

20

30

40

50

60

70

960966972978984990996

1002100810141020102610321038104410501056106210681074108010861092109811041110111611221128

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

0

10

20

30

40

50

60

1083108910951101110711131119112511311137114311491155116111671173117911851191119712031209121512211227123312391245125112571263

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 34 of 51

Figure 30. Classification of spectral lines for the 1,326 Hz tone (typical in the 12 m/s bin) 

0

5

10

15

20

25

30

35

40

45

50

12271236124512541263127212811290129913081317132613351344135313621371138013891398140714161425

Sound Pressure Level [dB]

Frequency [Hz]

Masking

Tone

Neither

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 35 of 51

6.6 Uncertainty

The type A uncertainties for sound power levels, one-third octave levels, and tonality were 

calculated using the methods prescribed in the Standard. The type B uncertainty components are 

shown in Table 15. 

Table 15. Type B Uncertainty Components for Sound Power Levels and Tonality

Var

Description 

Type B 

Uncertainty 

for Sound 

Power Level

Type B 

Uncertainty for 

One-Third 

Octave Levels

Type B 

Uncertainty 

for Tonality

Comment

UB1 Calibration 0.2 0.2 0.1 Assumption, used typical 

value

UB2 Instrument 0.2 0.2 0.2 Assumption, used typical 

value

UB3 Board 0.3 1.7 1.7 The board was placed well, 

used typical value

UB4 Distance 0.1 0.1 0.05 Assumption, used typical 

value

UB5 Impedance 0.1 0.1 0.1 Assumption, used typical 

value

UB6 Turbulence 0.4 0.4 0.2 Assumption, used typical 

value

UB7

Wind speed, 

measured

Varies with 

wind speed

Varies with wind 

speed and onethird octave 

center 

frequency bin

0.6

Calculated per IEC 61400-12-

1 Ed. 1.0, 205-12 and 

converted to dBA for SPL and 

TOB. 

Typical value for tonality

UB8 Direction 0.3 0.3 0.3 Assumption, used typical 

value

UB9 Background Varies with 

wind speed

Varies with wind 

speed and onethird octave 

center 

frequency bin

Varies by 

tone

Standard deviation of the 

applied correction

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Viryd IEC Acoustic Noise Report 130319 Page 36 of 51

7 Exceptions

7.1 Exceptions to the Standard

NREL engineers altered the analysis for the small wind turbine. Ten-second averages were used 

in the analysis instead of 1-minute averages to better characterize the dynamic nature of this 

small wind turbine. In addition, binning by wind speed was used instead of regression analysis, 

and the integer values were calculated by interpolating between bins and extrapolating at the 

ends. 

7.2 Exceptions to the Quality Assurance System

There were no exceptions to NREL’s quality assurance system.

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National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 37 of 51

References

International Electrotechnical Commission (IEC). (2006). Wind Turbine Generator Systems – 

Part 11 Acoustic Noise Measurement Techniques, IEC 61400-11, Ed 2.1, 2006-11, Geneva, 

Switzerland.

Roadman, J., Murphy, M., Huskey, A., van Dam, J. (2011). Internal report. Acoustic Noise Test 

Plan for the Viryd CS8 Wind Turbine. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 38 of 51

Appendix A. Pictures

Figure A1. The sound board during the test 

(Photo by Jason Roadman, NREL) 

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at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 39 of 51

Figure A2. Test turbine, as viewed from the reference microphone position 

(Photo by Jason Roadman, NREL) 

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National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 40 of 51

Figure A3. Test turbine, as viewed from the meteorological mast 

(Photo by Jason Roadman, NREL) 

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Viryd IEC Acoustic Noise Report 130319 Page 41 of 51

Appendix B. Calibration Sheets

Figure B1. Calibration sheet for the microphone 2406812 

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Viryd IEC Acoustic Noise Report 130319 Page 42 of 51

Figure B2. Calibration sheet for the sound level meter

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National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 43 of 51

Figure B3. Calibration sheet for the acoustic calibrator

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 44 of 51

Figure B4. Calibration sheet for the primary anemometer

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 45 of 51

Figure B5. Page 1 of the power transducer calibration sheet

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 46 of 51

Figure B6. Calibration sheet for the pressure transducer

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 47 of 51

Figure B7. Calibration sheet for the temperature sensor

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 48 of 51

Figure B8. Calibration sheet for the wind vane

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 49 of 51

Figure B9. Calibration sheet for the 9205 signal conditioning module 14DA726

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 50 of 51

Figure B10. Calibration sheet for the 9217 signal conditioning module 12BFEE2

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
Viryd IEC Acoustic Noise Report 130319 Page 51 of 51

Figure B11. Calibration sheet for the 9229 signal conditioning module 12A2037

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.