Assessing acoustic emissions from
wind turbines
18 November 2013

Jon Cooper
Resonate Acoustics
Outline
General introduction to wind
farm criteria and acoustic
terminology.
A-weighted levels, predicting
wind farm noise...
Noise Standards used in Australia
Variety of Standards in use/proposed for wind farms:

- South Australian Wind farms envi...
Wind Farm Criteria
Criteria can generally be simplified to:

“The sound level from the operating wind energy facility shal...
Acoustic Terminology
Sound is a pressure wave in air travelling at approximately
340 m/s.
Frequency refers to ‘how often’ ...
Decibels (dB)
The human ear has incredible sensitivity and
dynamic range: 0.00002 Pa to 200 Pa.
Decibels compresses this s...
Why we use A-weighting
We don’t hear sound all frequencies equally. A-weighting
roughly approximates human hearing.
A-weighted assessment process
The following steps are undertaken:

1. Determine existing ‘Background’ (LA90) noise levels....
Step 1&2 – Background / Criteria
Measurement of Background noise is relatively straight forward.

Only issue can be making...
Step 3 – Predictions
Several noise models to chose from, with many parameters to
alter.
The various Guidelines / Standards...
Step 3 – Predictions
Topography is very important (concave slopes result in
measured levels 3 dB(A) higher than flat sites...
Step 3 – Predictions
With the correct model (for the site topography and
measurement method) predictions can be remarkably...
Step 4 – Compliance measurement
Normally relatively straight forward, particularly with up to date
background measurements...
Why not just dB(A)?
A-weighting is relatively simple to use, but not a complete
descriptor of human response. A persons fe...
Tonality – Introduction
Particular frequency that draws attention of listeners (whistle,
whine, ringing, rumble…..). Can b...
Tonality – Turbine data
Manufacturers measure tonality using IEC 61400-11.

Most data measured against Edition 2.1, rather...
Tonality – Example
Tonality can be hard to find. Turbine model had passed some
IEC 2.1 tonality tests at the turbine, but ...
Tonality – Example
Detection of tone (tonal audibility > 0 dB) at residence. Limited
to night time, winds of 5 – 6 m/s (hu...
Tonality – Example
Average tonal audibility at turbine. Audibility lowest at downwind
measurement location.
Average audibi...
Tonality – Example
Tone was found to result from gear meshing, and was being
radiated off the blades of the turbine.
Tonal...
Amplitude modulation
Some degree of amplitude modulation is a normal part of wind
turbine noise (swish noise from blades)....
Amplitude modulation
Some degree of amplitude modulation is a normal part of wind
turbine noise (swish noise from blades)....
Amplitude modulation
NZS 6808:2010 criteria are easy to apply for a single 2 minute
measurement, but very difficult to aut...
Low Frequency Noise
Low frequency noise criteria contained in both the Draft NSW
and Draft Victorian Guidelines.
Criteria ...
What is infrasound?
Infrasound is the frequencies below the “audible range” (sound
at 1 Hz – 20 Hz).
We can hear this
soun...
What is infrasound?
Infrasound is all around us. Sources include; vehicles, Air
conditioners, wind, waves, industry, peopl...
Effects of infrasound
How do we perceive infrasound? – we hear it first. If it’s really
loud we will then also feel it.
Lu...
What level of infrasound is ok?
Criteria can be based on perception – historically worked well
for other industrial noise ...
Infrasound Study Background
11 sites (some have multiple measurement locations)

Urban offices, urban houses
Rural houses ...
Infrasound Results
At residential distances, the infrasound from wind turbines is at
a lower level than other sources.
Loc...
Future directions
Likely to be a number of changes and refinements to criteria.

Debate over 35 dB(A) or 40 dB(A) lower li...
Future directions
Real-time monitoring….

Several difficulties:
- Criteria currently set as average (typically 2 week), ra...
Questions
jon.cooper@resonateacoustics.com
Upcoming SlideShare
Loading in …5
×

Jon Cooper, Resonate Accoustics: Measuring and analysing acoustic emissions from wind turbines with particular focus on special audible characteristics

541 views
349 views

Published on

Jon Cooper, Associate Director, Resonate Acoustics delivered this presentation at 2013 Australian Wind Energy Conference. The event gave conference attendees key insights into how the new Abbott Government may impact future developments in the industry. The conference has a long-standing history of bring together key policy stakeholders, government representatives, project developers, energy companies and regulators. For more information about the annual event, please visit the conference website: https://www.informa.com.au/windenergyconference.

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
541
On SlideShare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
16
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Jon Cooper, Resonate Accoustics: Measuring and analysing acoustic emissions from wind turbines with particular focus on special audible characteristics

  1. 1. Assessing acoustic emissions from wind turbines 18 November 2013 Jon Cooper Resonate Acoustics
  2. 2. Outline General introduction to wind farm criteria and acoustic terminology. A-weighted levels, predicting wind farm noise levels and measuring it. Special audible characteristics. Future directions in criteria and wind farm noise assessments. Discussion / Questions
  3. 3. Noise Standards used in Australia Variety of Standards in use/proposed for wind farms: - South Australian Wind farms environmental noise guidelines 2009 - South Australian Wind farms environmental noise guidelines 2003 - New Zealand Standard 6808:2010 - New Zealand Standard 6808:1998 - Australian Standard 4959:2010 - Draft National Guidelines July 2010 - Draft NSW Planning Guidelines: Wind Farms - Draft Victorian Wind Farm Noise Supplementary Guidance for NZ Standard 6808 All different, but there is a common theme.
  4. 4. Wind Farm Criteria Criteria can generally be simplified to: “The sound level from the operating wind energy facility shall not exceed 40 dB(A) or the background level (LA90) by more than 5 dB(A), whichever is the greater.” “If sound has a special audible characteristic the measured sound level shall have a 5 dB(A) penalty applied.”
  5. 5. Acoustic Terminology Sound is a pressure wave in air travelling at approximately 340 m/s. Frequency refers to ‘how often’ the air particles vibrate. Often said that humans can hear at frequencies of 20 Hz – 20,000 Hz (the “audible range”) Hertz (Hz) = 1 cycle per second 100 Hz 1,000 Hz 10,000 Hz
  6. 6. Decibels (dB) The human ear has incredible sensitivity and dynamic range: 0.00002 Pa to 200 Pa. Decibels compresses this scale, makes life easier. 2 to 3 dB change is barely perceptible 5 dB change is easily noticeable 10 dB change is a doubling or halving of loudness
  7. 7. Why we use A-weighting We don’t hear sound all frequencies equally. A-weighting roughly approximates human hearing.
  8. 8. A-weighted assessment process The following steps are undertaken: 1. Determine existing ‘Background’ (LA90) noise levels. 2. Criteria = 40 dB(A) or Background + 5 dB(A). 3. Predict wind farm level, check for compliance with criteria. 4. Once constructed measure total wind farm + background noise level. Confirm that this is less than criteria.
  9. 9. Step 1&2 – Background / Criteria Measurement of Background noise is relatively straight forward. Only issue can be making sure up to date criteria is available at locations where compliance measurements may be needed. Criteria based on measurements 10 years ago can be very difficult to later demonstrate compliance. Get background measurements at likely complaint locations. With good background noise data step 2 is straight forward.
  10. 10. Step 3 – Predictions Several noise models to chose from, with many parameters to alter. The various Guidelines / Standards all have different compliance measurement techniques. Different method = different compliance result (up to 2.5 dB(A) difference) Necessary to consider the measurement method when selecting the noise model to be used.
  11. 11. Step 3 – Predictions Topography is very important (concave slopes result in measured levels 3 dB(A) higher than flat sites) None of the models properly calculates topography's influence.
  12. 12. Step 3 – Predictions With the correct model (for the site topography and measurement method) predictions can be remarkably accurate. Typically use ISO 9613 with hard ground (G = 0) for concave topography. ISO 9613 with 50% hard (G = 0.5) for flat sites. Wrong model / compliance measurement method = trouble. NSW criteria particularly are dangerous.
  13. 13. Step 4 – Compliance measurement Normally relatively straight forward, particularly with up to date background measurements.
  14. 14. Why not just dB(A)? A-weighting is relatively simple to use, but not a complete descriptor of human response. A persons feelings towards the source are very important. Sound may also be more noticeable (annoying) than suggested by the A-weighted level if it includes; - Tonality - Modulation - Impulsive noise - Low frequency noise The above (+ infrasound)? are “Special Audible Characteristics”
  15. 15. Tonality – Introduction Particular frequency that draws attention of listeners (whistle, whine, ringing, rumble…..). Can be very annoying. Tonality is normally measured using the “tonal audibility” Tonal audibility of 0 dB = threshold of detection for a typical listener. Higher values are more audible. Criteria vary between states. - South Australia are the strictest (5 dB penalty for tonal audibility = 0 dB). - Victoria require tonal audibility of 4 dB, sliding penalty. - NSW Draft guidelines use a third octave band test (approx. equivalent to tonal audibility of 6 dB).
  16. 16. Tonality – Turbine data Manufacturers measure tonality using IEC 61400-11. Most data measured against Edition 2.1, rather than Edition 3 (released 12 months ago). Both standards use measurements at the turbine, downwind +/-15 degrees. Both at approximately 6 – 10 m/s, 10m AGL. Edition 2.1 uses 2 minutes of data at each speed, Edition 3 averages all data. IEC Standard is often used for compliance measurements to check that tonality is not present.
  17. 17. Tonality – Example Tonality can be hard to find. Turbine model had passed some IEC 2.1 tonality tests at the turbine, but failed others. Tone not detected during multiple site visits at the residence. Resident was complaining about the character of the noise from the turbine under specific wind conditions. Nature of the complaint suggested tonality may be audible.
  18. 18. Tonality – Example Detection of tone (tonal audibility > 0 dB) at residence. Limited to night time, winds of 5 – 6 m/s (hub height). ~124 Hz tone occurrence with wind speed & time of day 0:00 - 3:00 21:00 - 00:00 Tone occurrence (%) 90-100 18:00 - 21:00 12:00 - 15:00 9:00 - 12:00 6:00 - 9:00 Time of day 80-90 15:00 - 18:00 70-80 60-70 50-60 40-50 30-40 20-30 3:00 - 6:00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hub Height Wind Speed (m/s) 15 16 17 18 19 0:00 - 3:00 20 10-20 0-10
  19. 19. Tonality – Example Average tonal audibility at turbine. Audibility lowest at downwind measurement location. Average audibility with wind speed/direction 124 Hz -180 -157.5 Average audibility (dB) -135 -112.5 4-5 -90 -45 -22.5 0 22.5 45 67.5 90 112.5 135 157.5 180 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Wind Speed (m/s) 3-4 Measurement angle -67.5 2-3 1-2 0-1 -1-0 -2--1 -3--2 -4--3 -5--4
  20. 20. Tonality – Example Tone was found to result from gear meshing, and was being radiated off the blades of the turbine. Tonal noise was rectified by fitting tuned mass dampers, confirmed through follow up measurements at the residence. Further info on method is available in paper published at Wind Turbine Noise 2013.
  21. 21. Amplitude modulation Some degree of amplitude modulation is a normal part of wind turbine noise (swish noise from blades). All the Guidelines note that amplitude modulation may at times become excessive. Assessment criteria limited. Objective criteria only included in NZS 6808:2010.
  22. 22. Amplitude modulation Some degree of amplitude modulation is a normal part of wind turbine noise (swish noise from blades). All the Guidelines note that amplitude modulation may at times become excessive. Assessment criteria limited – objective criteria only included in NZS 6808:2010.
  23. 23. Amplitude modulation NZS 6808:2010 criteria are easy to apply for a single 2 minute measurement, but very difficult to automate. Measured 100 ms Noise Level 100 ms Lp local minima local maxima Sound pressure level (dB) 30 25 20 15 10 5 0 0:00 0:05 0:10 0:15 0:20 Time (minutes:seconds) Limited justification for criterion set (no dose response). Modulation failing the criteria appears to be normal modulation. Extraneous noise hard to exclude. Awaiting the results of a study being run by RenewableUK.
  24. 24. Low Frequency Noise Low frequency noise criteria contained in both the Draft NSW and Draft Victorian Guidelines. Criteria use C-weighted outdoors measurements as a screening test, then UK indoor criteria. Wind noise on microphones is low frequency. Very likely outdoors C-weighted criteria will be failed. Difficult measuring in occupied house. Wind turbine noise unlikely to fail low frequency noise criteria.
  25. 25. What is infrasound? Infrasound is the frequencies below the “audible range” (sound at 1 Hz – 20 Hz). We can hear this sound if loud enough.
  26. 26. What is infrasound? Infrasound is all around us. Sources include; vehicles, Air conditioners, wind, waves, industry, people..... One of the best examples of perceptible (audible) infrasound is driving along in your car with the rear window down. Infrasound is just very low frequency sound
  27. 27. Effects of infrasound How do we perceive infrasound? – we hear it first. If it’s really loud we will then also feel it. Lundstrong experiment (1983) shows tiredness just above threshold of perception. No effect on deaf people at same noise level. Health effects – yes, but only at very high levels (audible sound is unbearable, whole room shaking) Below threshold of perception? - people feel sick after viewing material available on the internet, whether there is infrasound or not (Fiona Crichton study, 2013)
  28. 28. What level of infrasound is ok? Criteria can be based on perception – historically worked well for other industrial noise (85 dB(G)) Criteria could be based on the wind farm not being measurable – but everything else around us is a measureable source….. We could consider what is the normal level of infrasound in the environment. This is the approach taken in the joint study by the SA EPA and Resonate acoustics earlier this year.
  29. 29. Infrasound Study Background 11 sites (some have multiple measurement locations) Urban offices, urban houses Rural houses near both The Bluff, and Clements Gap wind farms Rural houses away from wind farms
  30. 30. Infrasound Results At residential distances, the infrasound from wind turbines is at a lower level than other sources. Location with the lowest level of infrasound was adjacent to a wind farm. Other measurements at Macarthur before and after commissioning showed no difference in level. Infrasound from wind turbines is not a problem.
  31. 31. Future directions Likely to be a number of changes and refinements to criteria. Debate over 35 dB(A) or 40 dB(A) lower limit. SA probably the only state to use 40 dB(A). Separate day and night time criteria likely. Somewhat overcomes shear, but also the noise due to activity. Criteria for Special audible characteristics will be refined: - RenewableUK Amplitude modulation work will be published, leading to new criteria. May be short term pain, likely to be able to be mitigated. - More detailed tonality assessments. - Low frequency criteria introduced – should comply, but hard to show.
  32. 32. Future directions Real-time monitoring…. Several difficulties: - Criteria currently set as average (typically 2 week), rather than instantaneous. - extraneous noise. - BG + 5 dB(A). Use historical BG or the BG at that moment in time? Real-time assessment of Special Audible Characteristics? Monitoring likely to require measurements away from a receiver, minimum rolling assessment period, and automated extraneous noise exclusion.
  33. 33. Questions jon.cooper@resonateacoustics.com

×