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Wind Farm Noise and

Excess Amplitude Modulation

Listening Room Exercise

at the National Physical Laboratory

11th July 2012

Introductory notes

The objective of the exercise is to try to replicate listening to wind farm noise and in

particular amplitude modulation in a home situation where the intent is rest and

relaxation. It is intended that there is minimal conversation during the playback so as

not to distort the purpose of the exercise and also to allow hearing to adjust to the

quieter environment.

The initial period of no playback followed by background noise is to allow some

acclimatisation of the hearing system. Some tracks are played to demonstrate the

experience of longer periods of AM and others to identify character in the noise.

This document provides a schedule of the playback, a glossary of terms, some

information on the prevalence of excess amplitude modulation (EAM) followed by a

page for each period of playback. These pages show a graph of the noise trace, any

relevant description or annotations and space for notes.

→ All graphs are related to BST (where appropriate)

→ Please note that the scale may vary between graphs.

Wind Farm Noise and EAM Listening Room Exercise

11/07/2012 of 31

Contents

Definition of (Excess) Amplitude Modulation……………….. 3

Schedule of playback………………………………………………… 4

Graphs of tracks……………………………………………………….. 7

Glossary…………………………………………………………………… 26

Prevalence of AM / EAM…………………………………………….. 28

Frequency comparator………………………………………………. 29

Example Graph…………………………………………………………. 30

Acknowledgements…………………………………………………… 31


11/07/2012 of 31

Aerodynamic / Amplitude Modulation

Comments in the report by Salford University for the UK Government 2007:

“The term AM indicates aerodynamic noise from wind turbines, but with a greater than

normal degree of regular fluctuation at blade passing frequency, typically once per

second. AM was considered to be a factor in four of the sites, and a possible factor in

another eight. Regarding the four sites, analysis of meteorological data suggests that

the conditions for AM would prevail between about 7% and 15% of the time.”

Some modulation of wind farm noise was foreseen by the authors of

ETSU-R-97:

“The noise levels recommended in this report take into account the character of noise

described as blade swish… The modulation or rhythmic swish emitted by wind turbines

has been considered to have characteristic that is irregular enough to attract

attention…Blade swish is an amplitude modulation of noise in the frequency range

which is associated with trailing edge noise… This rhythmic swish sound… is normally

centred around the 800-1000Hz region of the frequency band… This modulation of

blade noise may result in a variation of the overall A-weighted noise level by as much

of 3dB(A) (peak to trough) when measured close to a wind turbine. As distance from

the wind turbine / wind farm increases, this depth of modulation would be expected to

decrease as atmospheric absorption attenuated the higher frequency energy radiated

by the blade.”

Discussion in the DTI report by HMP 2006:

“The presence of high levels of amplitude modulation is not reported to occur for a

significant majority of wind farms or wind turbines. However, some wind farms clearly

result in modulation at night which is greater than that assumed within ETSU-R-97

Guidelines. The risk of aerodynamic modulation is believed to be greatest for sites

where stable atmospheric conditions occur and tall wind turbines are proposed /

operating or where high levels of wind shear exist at a site. In general, stable

atmospheric conditions are more likely to occur at level sites which are to be found in

the UK, i.e. eastern side of England for example. Site specific effects in hillier terrain,

due to topographical effects, might also result in such modulation.”


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Schedule of playback

Track Duration Min/Sec

Location Date Start time

No. turbines / nearest turbine

Notes Page no.

External measurements

1 2:00 00:00:00 7

2 2:00

Site D (remote rural

location)

2012

00:12:00

1km from the

wind farm

Rural background noise outside with no turbines

operating. Aims to provide perspective of external

background noise levels. External equivalent of

tracks 12 and 13. 8

3 4:40 00:55:17 This is a rural coastal location with excessive

Amplitude Modulation outside. 9

4 2:00 × 2 00:27:17

Starts with a car passing on main road which

partially but not totally masks the turbine noise.

This provides contrast. Many characteristics are

evident including the sudden drop in noise between

peaks.

10

5 2:00 × 2

Kessingland

10

June

2012

00:27:17

2 approx 550m

away (housing is

nearer than this) Same as track 4 but elevated by 13dB

to provide comparison with how much noise ETSU-

R-97 would allow before exceeding its lowest

possible night time limit. Without separate control of

AM this level of noise is then permitted.

11

6 3:00 × 2 Knabbs Ridge

8 March 2012

00:10:03 3 dominate, approx 550m

away

This track is recorded at a mobile home site where

many residents have sold up and moved out

because of the wind farm. The track starts with a

car on the road interspersed with turbine noise

which dominates as the car fades away.

Not all the turbines were audible or intrusive.

12

7 2:00 × 2 Site C

(remote rural location)

2012 16:55:31 450m from 3

turbines

The measurements were made in an external

amenity area location in a remote rural area. It is

450m from 3 turbines in a cross wind situation, not

downwind (Site C – anonymous to meet complainant

requirements). Dominating wind turbine noise at

least 10dB(A) above the background.

13


11/07/2012 of 31




Notes Page no.

8 1:00 23:05:03 In this example the character of the EAM changes

between one and two beats. 14

9 2:00

28

June 2012 23:44:22

If you listen carefully you can hear some laughter

nearby from a group of youths on a night out at this

coastal resort.

15

10 1:30

Kessingland

29

June 2012

00:09:52

630 metres from

2 turbines

The graph gives five excerpts of EAM showing the

range of different noise character throughout the

night.

16

11 2.00 Site D

(remote rural

location)

2012 00:56:36 1km from the wind farm

Comparison with turbines off and on approximately

30 minutes apart. Character of sound scape

significantly changed.

17

Internal measurements

12 2:00 00:00:00 18

13 2:00

Site D

(remote rural location)

2012

00:12:00

1km from the

wind farm

Rural background noise inside with no turbines

operating. Aims to provide perspective of internal

background noise levels. Internal equivalent of

tracks 1 and 2. 19

14 0:40 23:33:04 20

15 1:00

Kessingland 28 June 2012 23:36:04

Inside a car at 630 metres from the nearest of two

turbines

This is to provide perspective and comparison with

tracks 8-10 as it was recorded on the same night

and so gives an indication of noise within dwellings. 21

16 2:30 5 July 2007

21:00:03 22

17 3:30

Deeping St. Nicholas 4 July

2008 22:02:56

Inside a bedroom at Grays Farm

Deeping St. Nicholas 1050m

away from the wind farm.

The case can only be discussed in relation to those

elements in the public domain as there was a

settlement during proceedings in the High Court for

nuisance.

Track 16: AM can be heard but is not visible on the

graph.

Track 17: EAM is clearly visible and audible.

23


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Notes Page no.

18 2:00 × 2 02:52:04

There is an intermittent drone or tone that also

fluctuates in and out at times caused by the wind

farm. Please try to imagine attempting to get to

sleep with this. The drone / tone is no longer

evident in track 12 below, one hour later.

24

19 2:00 × 2

Site D 2012

03:52:03

Inside bedroom

1km from the

wind farm The impact is continuing an hour later. The average

levels are lower in sound energy and below the WHO

Guideline levels for steady continuous noise that

many acousticians apply as a limit of acceptability.

Some low frequency thumping is evident.

25

Please note: the purpose of this exercise is to demonstrate the character of wind farm noise, AM and EAM at an approximate

decibel level to that at which it was recorded. Although we have calibrated the recordings (measuring in accordance with

BS7445:2003) to within approximately 1-2dB of the level recorded in the field there will be discrepancies between the two. For

example, the decibel level heard by the listener will vary depending on their location in the room. There are also external noises

being played internally which will be altered due to the different acoustics in an open and enclosed space. If you have any queries

about the replication of the recorded noise for this exercise then please do not hesitate to ask.


11/07/2012 of 31

Track 01 Site D - External background noise level

Site D00:00:00 - 00:02:00

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

Rural background noise level outside approximately 1km from a wind farm with no turbines

operating. It provides a perspective of typical internal background noise levels in rural

areas. The peaks are caused by animal noise. This extract corresponds to track 12 and is

its external equivalent.

NOTES


11/07/2012 of 31

Track 02 Site D - External background noise level

Site D00:12:00 - 00:14:00

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dB100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

Rural background noise level outside with no turbines operating. This extract corresponds

to track 13 and is its external equivalent.

NOTES


11/07/2012 of 31

Track 03 Kessingland - External Amplitude Modulation

Kessingland - 10 June 201200:55:17 - 00:59:59

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This is a rural location with excess amplitude modulation outside. It gives noise at levels

which are 5dB below the minimum daytime ETSU-R-97 limit and 13dB below the night time

limit allowed by the guidance. This period includes a period where there are double beat

peaks due to separate peaks from both the turbines.

NOTES


11/07/2012 of 31



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100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This track provides contrast. It starts with a car passing on a main road which partially but

not totally masks the turbine noise. The peak to trough variations recorded were previously

considered impossible by industry experts. Furthermore, the peak to trough variations were

considered to reduce over distance. This clip provides significant contrast with what is a

quiet environment absent the wind farm noise. Many characteristics are evident including

the sudden drop in noise between peaks.

NOTES


11/07/2012 of 31

Track 05 Kessingland - External Amplitude Modulation +13dB


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100 ms LAeq + 13dB

Period LAeq (calc)

Period LA90 (calc)

The wind turbine noise is elevated to provide comparison with how much noise ETSU-R-97

would allow before exceeding the lowest possible night time limit (43dB LA90). Without

separate control of amplitude modulation this level of noise is then permitted under the

current guidance. It is at the ETSU-R-97 limit of what would still be allowed under the

guidance. Whilst the peaks go above the ETSU-R-97 limit the LA90 (blue line) value does

not and ETSU-R-97 is based on this index.

NOTES


11/07/2012 of 31

Track 06 Knabbs Ridge - External Amplitude Modulation

Knabbs Ridge - 8 March 201200:10:03 - 00:13:02

THUMPING

LASHING

CAR ON ROAD - SOME AM THUMP DISCERNABLE

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dB(A)100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This track was recorded outside dwellings approximately 550m from the turbines. The impact is

mainly from two turbines. It starts with a car on the road interspersed with wind turbine noise.

The car fades away and the wind turbine noise then dominates. The track includes some

periods of rumbling / roar, thumping, lashing and also more typical wind turbine noise. Not all

turbines were audible or visible. Measurements were made at a mobile home site where many

residents have sold up and moved out because of the wind farm.

NOTES


11/07/2012 of 31

Track 07 Site C - External Amplitude Modulation

Site C16:55:31 - 16:57:31

BIRDS CALLS AUDIBLE

PERSON WALKS AWAY FROM MICROPHONE

BIRDS CALLS AUDIBLE

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dB(A)100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This site remains anonymous due to potential litigation. The measurements were made in an

external amenity area location in a remote rural area. It is 450m from 3 turbines in a cross

wind situation (as opposed to downwind). The wind turbine noise is dominating and at least

10dB above the background noise level. The track does not do justice to the intrusion

experienced. When actually heard, the changing direction of the noise added substantially to its

impact. This cannot be captured in a simple microphone. 40 seconds in (16:56:05) you can

hear birds in adjacent trees for comparison and also someone moving about (16:56:43) and at

other times (near the microphone). They finally walk away at 1 minute 15 seconds. More birds

are evident at 16:56:42 but the turbines dominate.

NOTES


11/07/2012 of 31



AM CONSISTS OF TWO CLEAR BEATS

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

In contrast to tracks 3-5 also taken at Kessingland this period gives a good example of

amplitude modulation where two distinct beats are heard as part of the peak rather than

one. This demonstrates the different character that turbine noise can manifest.

NOTES


11/07/2012 of 31



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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)LAUGHTER

(not visible on graphs)

If you listen carefully you can hear some laughter from a group of youths on a night out in

this coastal resort but the AM wholly dominates the noise environment and causes the

peaks.

NOTES


11/07/2012 of 31


Kessingland - 29 June 2012Extracts from 00:09:52 - 00:23:35

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dB100 ms LAeq

These shorter extracts demonstrate the different character of the noise. This is largely

dependent on the frequency content of the amplitude modulation but there is also some

contrast between single beats and double beats per peak.

NOTES


11/07/2012 of 31

Track 11 Site D - Extracts with turbines off and on

Site DExtracts from 00:56 (turbines off) and 01:22 (turbines on)

01:23:00 - 01:23:30 TURBINES ON

00:57:07 - 00:57:37 TURBINES OFF

01:22:00 - 01:22:30 TURBINES ON

00:56:36 - 00:57:06 TURBINES OFF

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dB

100 ms LAeq

The measurements were made in an external amenity area location in a remote rural area

approximately 1km from the wind farm. The graph compares a period when the turbines

are not operating with a period just under half an hour later when the turbines are

operating. There is approximately a 7dB increase in background noise level and the

character of the sound scape if significantly altered.

NOTES


11/07/2012 of 31

Track 12 Site D - Internal background noise level

Site D00:00:00 - 00:02:00

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This is the background noise level within a rural dwelling approximately 1km from a wind

farm. It provides a perspective of typical internal background noise levels in rural areas.

The peaks are caused by animal noise. This extract corresponds to track 1 and is its

internal equivalent.

NOTES


11/07/2012 of 31

Track 13 Site D - Internal background noise level

Site D00:12:00 - 00:14:00

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This is the background noise level within a rural dwelling approximately 1km from a wind

farm. It provides a perspective of typical internal background noise levels in rural areas.

This extract corresponds to track 2 and is its internal equivalent.

NOTES


11/07/2012 of 31

Track 14 Kessingland - Internal Amplitude Modulation

Kessingland (in car with window open) - 28 June 201223:33:04 - 23:33:42

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

Inside a car at 630m from two turbines This is to provide perspective and comparison with

tracks 8-10 as it was recorded on the same night and so gives an indication of noise within

dwellings. The window was open.

NOTES


11/07/2012 of 31

Track 15 Kessingland - Internal Amplitude Modulation

Kessingland (in car with window open) - 28 June 201223:36:04 - 23:37:19

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dB

100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

Inside a car at 630m from two turbines This is to provide perspective and comparison with

tracks 8-10 as it was recorded on the same night and so gives an indication of noise within

dwellings. The window was open.

NOTES


11/07/2012 of 31

Track 16 Deeping St Nicholas - Internal Amplitude Modulation

Deeping St Nicholas - 05 July 200721:00:03 - 21:02:33

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dB 1s LAeq

Period LAeq (calc)

Period LA90 (calc)

In this extract amplitude modulation is audible but not discernible on the graph. This was one

of the earlier amplitude modulation measurements MAS undertook to see the effect of sample

time. It shows the importance of using the correct sampling rate for the type of noise that is

being measured. The sound level meter in this example is averaging the noise level every

second; however, to gain a true representation of the nature of amplitude modulation a

sampling rate of 1/8th (125ms) or 1/10th (100ms) of a second is needed. Note: this case can

only be discussed in relation to those elements in the public domain as there was a settlement

during proceedings in the High Court for noise nuisance.

NOTES


11/07/2012 of 31

Track 17 Deeping St Nicholas - Internal Amplitude Modulation

Deeping St Nicholas - 04 July 200822:02:56 - 22:06:25

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dB125 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

As above, amplitude modulation was measured inside a bedroom at Grays Farm, Deeping

St Nicholas 1050m away from the wind farm but can now be seen as averaging is 1/8th

second. The peaks of amplitude modulation fade in and out throughout the period.

Note: this case can only be discussed in relation to those elements in the public domain as

there was a settlement during proceedings in the High Court for noise nuisance.

NOTES


11/07/2012 of 31

Track 18 Site D - Internal Amplitude Modulation

Site D02:52:04 - 02:54:04

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dB100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This measurement is taken 1km from the wind farm inside a bedroom with window open.

There is an intermittent drone or tone that also fluctuates in and out at times which is

caused by the wind farm. It does not happen all of the time and is not occurring long

enough to attract a decibel penalty using the procedure stated in ETSU-R-97; however, it is

still noticeable and arguably still disturbing. Please try to imagine sleeping with this. The

drone / tone is no longer evidence in track 19 below an hour later.

NOTES


11/07/2012 of 31

Track 19 Site D - Internal Amplitude Modulation

Site D03:52:03 - 03:54:03

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dB100 ms LAeq

Period LAeq (calc)

Period LA90 (calc)

This measurement is taken 1km from the wind farm inside a bedroom, the same as that in

track 18 above. The impact is still continuing an hour later. The average levels are lower in

sound energy and below the WHO Guideline levels for steady continuous noise that many

acousticians apply as a limit of acceptability. Some low frequency thumping is evident

(200-315Hz).

NOTES


11/07/2012 of 31

Glossary of terms

Aerodynamic noise*

Noise emitted by a wind turbine due to the passage of air over the blades.

‘A’ Weighting This is a function which attempts to simulate the characteristics of

human hearing. See also dB(A) below.

Background

Noise*

The ambient noise level already present within the environment in the

absence of wind farm operation.

Blade Passing

Frequency*

The frequency at which blades pass over the tower i.e. three times

rotational speed for a three bladed machine.

Blade Swish* The modulation of broadband noise at blade passing frequency.

Decibel (dB(A)) A logarithmic unit in which sound is measured. dB(A) relates to

decibels measured on a sound level meter weighted by a scale which is designed to reflect the weighting placed on noise by the human ear.

A noise meter incorporates a frequency weighting device to create this differentiation. The dB(A) scale is now widely accepted. Measurements in dB(A) broadly agree with people’s assessment of

loudness for broadband noise. A change of 3dB(A) is the minimum perceptible under normal conditions, and a change of 10dB(A)

corresponds roughly to halving or doubling the loudness of a sound.

Excess Amplitude

Modulation (EAM)

This is the term that has commonly been used to express amplitude modulation noise from wind turbines / wind farms that was not

foreseen or discussed in ETSU-R-97, i.e. modulation noise greater than 3dB(A) (peak to trough) and below the frequency range of 800-

1000Hz. It is also a level identified as causing significant impact and not just that not included in ETSU-R-97 limits.

Frequency This is the number of air vibrations or pressure fluctuations per

second. The unit is the hertz (Hz). See also pitch.

Hertz (Hz)* The unit of frequency measurement representing cycles per second.

LA90 The A weighted noise level exceeded for 90% of the specified measurement period. It is a statistical measurement and now generally it is used to define background noise level. Thus if it was

measured for 1 minute it would equate to the quietest 6 seconds. In one hour it would be the quietest 10% of time or 6 minutes. Thus if

a machine ran continuously without a reduction in noise for 54 minutes and then stopped it would represent the quiet 6 minutes but if it ran for 55 minutes it would represent the quietest period of

machine noise.


11/07/2012 of 31

LAeq The A weighted equivalent continuous sound level - the sound level of a notionally steady sound having the same energy as a fluctuating

sound over a specified measurement period. LAeq is used to describe

many types of noise and can be measured directly with an integrating

sound level meter. It is obtained by continuously integrating (‘adding up the energy of’) a fluctuating sound signal and dividing by the elapsed time, to give the true mathematical average of any time

varying signal. An LAeq reading must always be related to a time

period, it should not be read as an instantaneous value of sound

pressure.

Masking* The process by which threshold of audibility of one sound is raised by the presence of another (masking) sound.

Modulation* Periodic variation in phase, frequency or amplitude but most commonly in amplitude when associated with wind turbine noise.

Pitch Frequency is an objective measure whereas the term pitch is subjective, and although mainly dependent on frequency is also affected by intensity.

Tones / Tonal Noise*

Noise containing a discrete frequency component most often of mechanical origin.

Wind Shear* A description of the increase in wind speed with height above ground level.

* definitions taken from ETSU-R-97

Reports:

→ ETSU-R-97 (1997) The assessment and rating of noise from wind farms.

→ DTI (2006) The measurement of low frequency noise at three UK wind

farms. Issued by the DTI in July 2006.

→ University of Salford for BERR (2007) Research into Aerodynamic

Modulation of Wind Turbine Noise.


11/07/2012 of 31

Prevalence of AM / EAM - the wind farms / turbine developments below have all been noted as generating AM / EAM noise

Wind Farm Location Turbine modelMW per

turbine

No. of

turbinesMW total

Hub Height

(m)Reference

Askham Cumbria V47 660kW 7 4.62 40 Salford - clear case added

Bears Down Cornwall Bonus 600kW 16 9.6 30 Salford - clear case added

Bicker Fen Lincolnshire Repower MM82 2MW 13 26 59 Statement from complainant - clear case

Black Law, Forth South Lanarkshire Siemens 2.3MW 42 97 82 MAS have no direct evidence

Blaen Bowi Carmarthenshire Nordex 1.3MW 3 3.9 46 Salford - clear case but not added

Blaengwen (statkraft) Multiple complaints

Carland Corss Cornwall Vesta WD34 400kw 15 6 30 In ETSU-R-97 and Salford

Causeymire Highland Bonus 2.3MW 21 48.3 60 In Salford but not added by Salford

Coal Clough Lancashire Vestas WD34 400kw 24 9.6 30 In ETSU-R-97 missed in Salford

Cold Northcott Cornwall WEG MS3-300 300kw 22 6.3 25 In ETSU-R-97 - in Salford but not added

Coldham Cambridgeshire Vestas V.80 1.75MW 8 14 60 Statements from complainant

Conisholme Bonus 2.3MW 21 48.3 MAS have no direct evidence

Cruach Mhor Argyll & Bute Vestas V52 850kw 35 29.75 45 Salford - but not added

Crystal Rig Scottish Borders Siemens 2.3 2.3MW 51 + 9 117.3 + 20.7 60 + 80 MAS have no direct evidence

Darracott Devon Gamesa G5 850kW 3 2.55 50 Complaints by residents of AM

Deeping St Nicholas Lincolnshire Repower MM82 2MW 8 16 59 In Salford and added, MAS confirmed

Delabole Cornwall Enercon E70 2.3MW 4 9.2 99 (tip) Direct complaints and advice of acoustician

Forestmoor, Bradworthy Devon Vestas 1.0 1MW 3 2.7 48 MAS have no direct evidence

Fullabrook Devon Vestas V90 3MW 22 66 65 Complaints by many residents of AM, post Salford

Gedney Marsh (Red House) Lincolnshire Repower MM82 2MW 6 12 59 MAS have no direct evidence

Glens of Foundland Aberdeenshire Bonus 1.3MW 20 26 46 In Salford but not added

Hadyard Hill South Ayrshire bonus 2.3 2.5MW 52 130 60-70 In Salford, possible case, but no direct evidence

Hafoty Ucha Gwynedd V52 850kW 1 0.85 39-44 In Salford, questionable case, but no direct evidence

Harlock Hill Cumbria Wind World 500kW 5 2.5 35 MAS have no direct evidence

High Volts County Durham NM80/2750 2750kW 3 7.85 60 MAS have no direct evidence

Kessingland Suffolk Repower MM92 2.05MW 2 4.1 80 MAS measured, post Salford

Knabs Ridge North Yorkshire Repower MM70 2MW 8 16 58 Complaints and MAS measured - post Salford

Llyn Alaw Anglesey Bonus 600kW 34 20.4 31 In Salford and WAS added

Lynch Knoll Gloucestershire Enercon E40 500kW 1 0.5 42 In Salford but not added

Mablethorpe Lincolnshire Enercon E40 600kW 2 1.2 65 MAS have no direct evidence

Michelin Tyre Factory Dundee City Enercon E70 2MW 2 4 85 In Salford but not added

Mynydd Clogau Powys Vestas 850kW 17 14.45 34 In Salford, possible case, but no direct evidence

North Pickenham Norfolk Vestas V90 1.8MW 8 14.4 80 MAS measured - residents not complaining officially

Penrhyddlan & Llidiatywaun 45 MAS have no direct evidence, but noise problems noted in ETSU-R-97

Red Tile / Warboys Cambridgeshire Repower MM82 2MW 12 24 59 MAS measured and complaints - missed by Salford

Rhyd y Groes Ceredigion Bonus B300 300kW 24 7.2 31 MAS have no direct evidence, but noise problems noted in ETSU-R-97

Royd Moor South Yorkshire Bonus 500 500kW 13 6.5 35 In Salford but not added, MAS heard

Site C MAS measured, complaints from residents, post Salford cannot disclose

St Breock Cornwall Bonus 450kW 11 4.95 35 MAS have no direct evidence

Swaffham Norfolk Enercon E82 1.8MW 1 1.8 67 Complaints and MAS measured, missed by Salford

Tir Mostyn & Foel Goch Denbighshire Gamesa 850kW 25 21.25 49 In Salford but not added

Trysglwyn Gwynedd Bonus 400kW 14 5.6 25 In Salford but not added

Wharrels Hill, Bothel Cumbria Nordex N60 1.3MW 8 10.4 76 Complaints by residents of AM, post Salford


11/07/2012 of 31

Frequency comparator

(sourced from http://www.music.vt.edu/musicdictionary/appendix/pitch/pitch.html)

156Hz - 416Hz

Approximate range

observed and measured

by MAS for EAM of

160-400Hz.

784Hz - 1047Hz

approximate ETSU-R-

97 range for AM /

blade swish of 800-

1000Hz

Middle C

262Hz

Bird calls

typically

1600Hz and

above

82Hz - lowest

note of the

(male) bass

singing range


11/07/2012 of 31

Example graph

30

35

40

45

50

55

60

23:0

7:30

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7:32

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7:33

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7:35

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7:39

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7:40

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7:42

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7:44

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7:45

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7:59

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8:01

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8:06

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8:07

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8:09

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8:12

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8:28

23:0

8:29

dB

The y-axis gives the decibel

level, i.e. how loud the noise is.

The x-axis gives the time in GMT or BST where appropriate

The rise (peak) and fall

(trough) in sound energy is

what we refer to as

amplitude modulation and

it is this change in sound

level that we hear as a 'thump' / 'whoosh'.

peak

trough

The 100ms LAeq shows how the noise level is varying with time.

The Period LAeq is a way of

expressing the 'average'

noise level for the time period

shown on the graph. If all the

time varying sound energy is

taken and expressed as a

single unvarying value, this gives the LAeq.

The Period LA90 is the

background noise level

for the time period shown

on the graph. It is a

statistical descriptor of the

noise - the quietest 10%

of noise in the period.


11/07/2012 of 31

Acknowledgements

This wind farm noise and EAM listening room exercise was presented by MAS

Environmental with the support of the Renewable Energy Foundation.

For more information please see below.

MAS Environmental

http://www.masenv.co.uk/

email: [email protected]

Renewable Energy Foundation

http://www.ref.org.uk/

wind farm noise and excess amplitude modulation listening ... environmental... · wind farm noise...

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