Listening Room Graphs Doc120709 FINAL

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 mi nimal 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 th e 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

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

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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

Duration Start No. turbines / Page Track Location Date Notes Min/Sec time nearest turbine no.

External measurements

1 2:00 Site D 00:00:00 1km from the Rural background noise outside with no turbines 7 operating. Aims to provide perspective of external (remote rural 2012 wind farm background noise levels. External equivalent of 2 2:00 location) 00:12:00 tracks 12 and 13. 8

This is a rural coastal location with excessive 3 4:40 00:55:17 9 Amplitude Modulation outside. Starts with a car passing on main road which 10 2 approx 550m partially but not totally masks the turbine noise. 4 2:00 × 2 00:27:17 This provides contrast. Many characteristics are 10 Kessingland June away (housing is evident including the sudden drop in noise between peaks. 2012 nearer than this) Same as track 4 but elevated by 13dB to provide comparison with how much noise ETSU- 5 2:00 × 2 00:27:17 R-97 would allow before exceeding its lowest 11 possible night time limit. Without separate control of AM this level of noise is then permitted. This track is recorded at a mobile home site where 8 3 dominate, many residents have sold up and moved out Knabbs because of the wind farm. The track starts with a 6 3:00 × 2 March 00:10:03 approx 550m 12 Ridge car on the road interspersed with turbine noise 2012 away which dominates as the car fades away. Not all the turbines were audible or intrusive. The measurements were made in an external Site C amenity area location in a remote rural area. It is 450m from 3 450m from 3 turbines in a cross wind situation, not 7 2:00 × 2 (remote rural 2012 16:55:31 13 turbines downwind (Site C – anonymous to meet complainant location) requirements). Dominating wind turbine noise at least 10dB(A) above the background.

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Duration Start No. turbines / Page Track Location Date Notes Min/Sec time nearest turbine no. In this example the character of the EAM changes 8 1:00 23:05:03 14 28 between one and two beats. June If you listen carefully you can hear some laughter 2012 630 metres from 9 2:00 Kessingland 23:44:22 nearby from a group of youths on a night out at this 15 2 turbines coastal resort. 29 The graph gives five excerpts of EAM showing the 10 1:30 June 00:09:52 range of different noise character throughout the 16 2012 night. Site D 1km from the Comparison with turbines off and on approximately 11 2.00 (remote rural 2012 00:56:36 30 minutes apart. Character of sound scape 17 wind farm location) significantly changed.

Internal measurements

12 2:00 Site D 00:00:00 Rural background noise inside with no turbines 18 1km from the operating. Aims to provide perspective of internal (remote rural 2012 wind farm background noise levels. Internal equivalent of 13 2:00 location) 00:12:00 tracks 1 and 2. 19

Inside a car at 14 0:40 28 23:33:04 20 630 metres from This is to provide perspective and comparison with Kessingland June tracks 8-10 as it was recorded on the same night the nearest of two 2012 and so gives an indication of noise within dwellings. 15 1:00 23:36:04 turbines 21 5 July Inside a bedroom The case can only be discussed in relation to those 16 2:30 21:00:03 22 2007 at Grays Farm elements in the public domain as there was a Deeping St. Deeping St. settlement during proceedings in the High Court for nuisance. Nicholas 4 July Nicholas 1050m 17 3:30 22:02:56 Track 16: AM can be heard but is not visible on the 23 2008 away from the graph. wind farm. Track 17: EAM is clearly visible and audible.

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Duration Start No. turbines / Page Track Location Date Notes Min/Sec time nearest turbine no. There is an intermittent drone or tone that also fluctuates in and out at times caused by the wind 18 2:00 × 2 02:52:04 farm. Please try to imagine attempting to get to 24 Inside bedroom sleep with this. The drone / tone is no longer evident in track 12 below, one hour later. Site D 2012 1km from the The impact is continuing an hour later. The average wind farm levels are lower in sound energy and below the WHO 19 2:00 × 2 03:52:03 Guideline levels for steady continuous noise that 25 many acousticians apply as a limit of acceptability. Some low frequency thumping is evident.

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.

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Track 01 Site D - External background noise level NOTES

Site D dB 00:00:00 - 00:02:00 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

00:00:08 00:00:10 00:00:13 00:00:15 00:00:18 00:00:20 00:00:22 00:00:25 00:00:27 00:00:30 00:00:32 00:00:34 00:00:37 00:00:39 00:00:42 00:00:44 00:00:46 00:00:49 00:00:51 00:00:54 00:00:56 00:00:58 00:01:01 00:01:03 00:01:06 00:01:08 00:01:10 00:01:13 00:01:15 00:01:18 00:01:20 00:01:22 00:01:25 00:01:27 00:01:30 00:01:32 00:01:34 00:01:37 00:01:39 00:01:42 00:01:44 00:01:46 00:01:49 00:01:51 00:01:54 00:01:56 00:01:58 00:02:01 00:02:03 00:02:06 00:02:08

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.

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Track 02 Site D - External background noise level NOTES

Site D dB 00:12:00 - 00:14:00 100 ms LAeq Period LAeq (calc) 50 Period LA90 (calc)

00:12:02 00:12:04 00:12:07 00:12:09 00:12:12 00:12:14 00:12:16 00:12:19 00:12:21 00:12:24 00:12:26 00:12:28 00:12:31 00:12:33 00:12:36 00:12:38 00:12:40 00:12:43 00:12:45 00:12:48 00:12:50 00:12:52 00:12:55 00:12:57 00:13:00 00:13:02 00:13:04 00:13:07 00:13:09 00:13:12 00:13:14 00:13:16 00:13:19 00:13:21 00:13:24 00:13:26 00:13:28 00:13:31 00:13:33 00:13:36 00:13:38 00:13:40 00:13:43 00:13:45 00:13:48 00:13:50 00:13:52 00:13:55 00:13:57 00:14:00 00:14:02

Rural background noise level outside with no turbines operating. This extract corresponds to track 13 and is its external equivalent.

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Track 03 Kessingland - External Amplitude Modulation NOTES

Kessingland - 10 June 2012 dB 00:55:17 - 00:59:59 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

00:55:17 00:55:23 00:55:28 00:55:34 00:55:39 00:55:45 00:55:51 00:55:56 00:56:02 00:56:07 00:56:13 00:56:19 00:56:24 00:56:30 00:56:35 00:56:41 00:56:47 00:56:52 00:56:58 00:57:03 00:57:09 00:57:15 00:57:20 00:57:26 00:57:31 00:57:37 00:57:43 00:57:48 00:57:54 00:57:59 00:58:05 00:58:11 00:58:16 00:58:22 00:58:27 00:58:33 00:58:39 00:58:44 00:58:50 00:58:55 00:59:01 00:59:07 00:59:12 00:59:18 00:59:23 00:59:29 00:59:35 00:59:40 00:59:46 00:59:51 00:59:57

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.

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Track 04 Kessingland - External Amplitude Modulation NOTES

Kessingland - 10 June 2012 dB 00:27:17 - 00:29:16 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

00:27:17 00:27:19 00:27:22 00:27:24 00:27:27 00:27:29 00:27:31 00:27:34 00:27:36 00:27:39 00:27:41 00:27:43 00:27:46 00:27:48 00:27:51 00:27:53 00:27:55 00:27:58 00:28:00 00:28:03 00:28:05 00:28:07 00:28:10 00:28:12 00:28:15 00:28:17 00:28:19 00:28:22 00:28:24 00:28:27 00:28:29 00:28:31 00:28:34 00:28:36 00:28:39 00:28:41 00:28:43 00:28:46 00:28:48 00:28:51 00:28:53 00:28:55 00:28:58 00:29:00 00:29:03 00:29:05 00:29:07 00:29:10 00:29:12 00:29:15 00:29:17

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.

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Track 05 Kessingland - External Amplitude Modulation +13dB NOTES

Kessingland - 10 June 2012 dB 00:27:17 - 00:29:16 100 ms LAeq + 13dB 60 Period LAeq (calc) Period LA90 (calc)

00:27:32 00:27:34 00:27:37 00:27:39 00:27:42 00:27:44 00:27:46 00:27:49 00:27:51 00:27:54 00:27:56 00:27:58 00:28:01 00:28:03 00:28:06 00:28:08 00:28:10 00:28:13 00:28:15 00:28:18 00:28:20 00:28:22 00:28:25 00:28:27 00:28:30 00:28:32 00:28:34 00:28:37 00:28:39 00:28:42 00:28:44 00:28:46 00:28:49 00:28:51 00:28:54 00:28:56 00:28:58 00:29:01 00:29:03 00:29:06 00:29:08 00:29:10 00:29:13 00:29:15 00:29:18 00:29:20 00:29:22 00:29:25 00:29:27 00:29:30 00:29:32 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.

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Track 06 Knabbs Ridge - External Amplitude Modulation NOTES

Knabbs Ridge - 8 March 2012 00:10:03 - 00:13:02 dB(A) CAR ON ROAD - SOME AM 100 ms LAeq THUMP DISCERNABLE 50 Period LAeq (calc) Period LA90 (calc)

THUMPING

45 LASHING

00:10:03 00:10:07 00:10:10 00:10:14 00:10:17 00:10:21 00:10:25 00:10:28 00:10:32 00:10:35 00:10:39 00:10:43 00:10:46 00:10:50 00:10:53 00:10:57 00:11:01 00:11:04 00:11:08 00:11:11 00:11:15 00:11:19 00:11:22 00:11:26 00:11:29 00:11:33 00:11:37 00:11:40 00:11:44 00:11:47 00:11:51 00:11:55 00:11:58 00:12:02 00:12:05 00:12:09 00:12:13 00:12:16 00:12:20 00:12:23 00:12:27 00:12:31 00:12:34 00:12:38 00:12:41 00:12:45 00:12:49 00:12:52 00:12:56 00:12:59

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.

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Track 07 Site C - External Amplitude Modulation NOTES

Site C 16:55:31 - 16:57:31 dB(A) 100 ms LAeq 60 Period LAeq (calc) Period LA90 (calc)

BIRDS CALLS 55 BIRDS CALLS AUDIBLE AUDIBLE PERSON WALKS AWAY FROM MICROPHONE 50

16:55:31 16:55:33 16:55:36 16:55:38 16:55:41 16:55:43 16:55:45 16:55:48 16:55:50 16:55:53 16:55:55 16:55:57 16:56:00 16:56:02 16:56:05 16:56:07 16:56:09 16:56:12 16:56:14 16:56:17 16:56:19 16:56:21 16:56:24 16:56:26 16:56:29 16:56:31 16:56:33 16:56:36 16:56:38 16:56:41 16:56:43 16:56:45 16:56:48 16:56:50 16:56:53 16:56:55 16:56:57 16:57:00 16:57:02 16:57:05 16:57:07 16:57:09 16:57:12 16:57:14 16:57:17 16:57:19 16:57:21 16:57:24 16:57:26 16:57:29 16:57:31

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.

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Track 08 Kessingland - External Amplitude Modulation NOTES

Kessingland - 28 June 2012 dB 23:05:03 - 23:06:02 100 ms LAeq 60 Period LAeq (calc) Period LA90 (calc)

AM CONSISTS OF TWO CLEAR BEATS 50

23:05:03 23:05:04 23:05:05 23:05:07 23:05:08 23:05:09 23:05:10 23:05:11 23:05:13 23:05:14 23:05:15 23:05:16 23:05:17 23:05:19 23:05:20 23:05:21 23:05:22 23:05:23 23:05:25 23:05:26 23:05:27 23:05:28 23:05:29 23:05:31 23:05:32 23:05:33 23:05:34 23:05:35 23:05:37 23:05:38 23:05:39 23:05:40 23:05:41 23:05:43 23:05:44 23:05:45 23:05:46 23:05:47 23:05:49 23:05:50 23:05:51 23:05:52 23:05:53 23:05:55 23:05:56 23:05:57 23:05:58 23:05:59 23:06:01 23:06:02

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.

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Track 09 Kessingland - External Amplitude Modulation NOTES

Kessingland - 28 June 2012 dB 23:44:22 - 23:46:10 100 ms LAeq 60 Period LAeq (calc) Period LA90 (calc) LAUGHTER (not visible on graphs) 55

23:44:22 23:44:24 23:44:26 23:44:29 23:44:31 23:44:33 23:44:35 23:44:37 23:44:40 23:44:42 23:44:44 23:44:46 23:44:48 23:44:51 23:44:53 23:44:55 23:44:57 23:44:59 23:45:02 23:45:04 23:45:06 23:45:08 23:45:10 23:45:13 23:45:15 23:45:17 23:45:19 23:45:21 23:45:24 23:45:26 23:45:28 23:45:30 23:45:32 23:45:35 23:45:37 23:45:39 23:45:41 23:45:43 23:45:46 23:45:48 23:45:50 23:45:52 23:45:54 23:45:57 23:45:59 23:46:01 23:46:03 23:46:05 23:46:08 23:46:10

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.

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Track 10 Kessingland - External Amplitude Modulation NOTES

Kessingland - 29 June 2012 dB Extracts from 00:09:52 - 00:23:35 100 ms LAeq 60

00:09:52 00:09:54 00:09:56 00:09:58 00:10:01 00:10:03 00:10:05 00:10:08 00:10:10 00:10:14 00:10:17 00:10:19 00:10:21 00:10:24 00:10:26 00:10:28 00:10:30 00:10:33 00:10:35 00:10:41 00:10:43 00:10:46 00:10:48 00:10:50 00:10:52 00:10:55 00:10:57 00:10:59 00:11:02 00:11:04 00:13:36 00:13:39 00:13:41 00:13:43 00:13:46 00:13:48 00:13:50 00:13:52 00:23:25 00:23:27 00:23:29 00:23:32 00:23:34

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.

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Track 11 Site D - Extracts with turbines off and on NOTES

Site D dB Extracts from 00:56 (turbines off) and 01:22 (turbines on) 100 ms LAeq 50

01:22:00 - 01:22:30 01:23:00 - 01:23:30 TURBINES ON TURBINES ON 40

00:56:36 - 00:57:06 35 TURBINES OFF 00:57:07 - 00:57:37 TURBINES OFF 30

00:56:36 00:56:38 00:56:41 00:56:44 00:56:46 00:56:49 00:56:52 00:56:54 00:56:57 00:57:00 00:57:03 00:57:05 01:22:01 01:22:03 01:22:06 01:22:09 01:22:11 01:22:14 01:22:17 01:22:19 01:22:22 01:22:25 01:22:28 01:22:30 00:57:09 00:57:11 00:57:14 00:57:17 00:57:19 00:57:22 00:57:25 00:57:28 00:57:30 00:57:33 00:57:36 01:22:59 01:23:01 01:23:04 01:23:07 01:23:10 01:23:12 01:23:15 01:23:18 01:23:20 01:23:23 01:23:26 01:23:28

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.

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Track 12 Site D - Internal background noise level NOTES

Site D dB 00:00:00 - 00:02:00 100 ms LAeq 40 Period LAeq (calc) Period LA90 (calc)

00:00:03 00:00:05 00:00:08 00:00:10 00:00:13 00:00:15 00:00:17 00:00:20 00:00:22 00:00:25 00:00:27 00:00:29 00:00:32 00:00:34 00:00:37 00:00:39 00:00:41 00:00:44 00:00:46 00:00:49 00:00:51 00:00:53 00:00:56 00:00:58 00:01:01 00:01:03 00:01:05 00:01:08 00:01:10 00:01:13 00:01:15 00:01:17 00:01:20 00:01:22 00:01:25 00:01:27 00:01:29 00:01:32 00:01:34 00:01:37 00:01:39 00:01:41 00:01:44 00:01:46 00:01:49 00:01:51 00:01:53 00:01:56 00:01:58 00:02:01 00:02:03

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.

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Track 13 Site D - Internal background noise level NOTES

Site D dB 00:12:00 - 00:14:00 100 ms LAeq 40 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.

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Track 14 Kessingland - Internal Amplitude Modulation NOTES

Kessingland (in car with window open) - 28 June 2012 dB 23:33:04 - 23:33:42 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

23:33:04 23:33:05 23:33:06 23:33:06 23:33:07 23:33:08 23:33:09 23:33:10 23:33:10 23:33:11 23:33:12 23:33:13 23:33:14 23:33:14 23:33:15 23:33:16 23:33:17 23:33:18 23:33:18 23:33:19 23:33:20 23:33:21 23:33:22 23:33:22 23:33:23 23:33:24 23:33:25 23:33:26 23:33:26 23:33:27 23:33:28 23:33:29 23:33:30 23:33:30 23:33:31 23:33:32 23:33:33 23:33:34 23:33:34 23:33:35 23:33:36 23:33:37 23:33:38 23:33:38 23:33:39 23:33:40 23:33:41 23:33:42

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.

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Track 15 Kessingland - Internal Amplitude Modulation NOTES

Kessingland (in car with window open) - 28 June 2012 dB 23:36:04 - 23:37:19 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

23:36:04 23:36:05 23:36:07 23:36:08 23:36:10 23:36:11 23:36:13 23:36:15 23:36:16 23:36:17 23:36:19 23:36:20 23:36:22 23:36:23 23:36:25 23:36:26 23:36:28 23:36:29 23:36:31 23:36:32 23:36:34 23:36:35 23:36:37 23:36:39 23:36:40 23:36:42 23:36:43 23:36:44 23:36:46 23:36:47 23:36:49 23:36:50 23:36:52 23:36:53 23:36:55 23:36:56 23:36:58 23:36:59 23:37:01 23:37:02 23:37:04 23:37:06 23:37:07 23:37:08 23:37:10 23:37:11 23:37:13 23:37:14 23:37:16 23:37:17 23:37:19

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Track 16 Deeping St Nicholas - Internal Amplitude Modulation NOTES

Deeping St Nicholas - 05 July 2007 dB 21:00:03 - 21:02:33 1s LAeq Period LAeq (calc) 50 Period LA90 (calc)

21:00:33 21:00:36 21:00:39 21:00:42 21:00:45 21:00:48 21:00:51 21:00:54 21:00:57 21:01:00 21:01:03 21:01:06 21:01:09 21:01:12 21:01:15 21:01:18 21:01:21 21:01:24 21:01:27 21:01:30 21:01:33 21:01:36 21:01:39 21:01:42 21:01:45 21:01:48 21:01:51 21:01:54 21:01:57 21:02:00 21:02:03 21:02:06 21:02:09 21:02:12 21:02:15 21:02:18 21:02:21 21:02:24 21:02:27 21:02:30 21:02:33

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.

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Track 17 Deeping St Nicholas - Internal Amplitude Modulation NOTES

Deeping St Nicholas - 04 July 2008 dB 22:02:56 - 22:06:25 125 ms LAeq Period LAeq (calc) 50 Period LA90 (calc)

22:02:56 22:03:00 22:03:04 22:03:09 22:03:13 22:03:17 22:03:21 22:03:26 22:03:30 22:03:34 22:03:39 22:03:43 22:03:47 22:03:51 22:03:55 22:04:00 22:04:04 22:04:08 22:04:12 22:04:17 22:04:21 22:04:25 22:04:30 22:04:34 22:04:38 22:04:42 22:04:46 22:04:51 22:04:55 22:04:59 22:05:03 22:05:08 22:05:12 22:05:16 22:05:21 22:05:25 22:05:29 22:05:33 22:05:37 22:05:42 22:05:46 22:05:50 22:05:54 22:05:59 22:06:03 22:06:07 22:06:11 22:06:16 22:06:20 22:06:24

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 1/8 th 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.

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Track 18 Site D - Internal Amplitude Modulation NOTES

Site D 02:52:04 - 02:54:04 dB 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

02:52:04 02:52:06 02:52:09 02:52:11 02:52:14 02:52:16 02:52:18 02:52:21 02:52:23 02:52:26 02:52:28 02:52:30 02:52:33 02:52:35 02:52:38 02:52:40 02:52:42 02:52:45 02:52:47 02:52:50 02:52:52 02:52:54 02:52:57 02:52:59 02:53:02 02:53:04 02:53:06 02:53:09 02:53:11 02:53:14 02:53:16 02:53:18 02:53:21 02:53:23 02:53:26 02:53:28 02:53:30 02:53:33 02:53:35 02:53:38 02:53:40 02:53:42 02:53:45 02:53:47 02:53:50 02:53:52 02:53:54 02:53:57 02:53:59 02:54:02 02:54:04

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.

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Track 19 Site D - Internal Amplitude Modulation NOTES

Site D 03:52:03 - 03:54:03 dB 100 ms LAeq 50 Period LAeq (calc) Period LA90 (calc)

03:52:03 03:52:05 03:52:08 03:52:10 03:52:13 03:52:15 03:52:17 03:52:20 03:52:22 03:52:25 03:52:27 03:52:29 03:52:32 03:52:34 03:52:37 03:52:39 03:52:41 03:52:44 03:52:46 03:52:49 03:52:51 03:52:53 03:52:56 03:52:58 03:53:01 03:53:03 03:53:05 03:53:08 03:53:10 03:53:13 03:53:15 03:53:17 03:53:20 03:53:22 03:53:25 03:53:27 03:53:29 03:53:32 03:53:34 03:53:37 03:53:39 03:53:41 03:53:44 03:53:46 03:53:49 03:53:51 03:53:53 03:53:56 03:53:58 03:54:01 03:54:03

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).

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Glossary of terms

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

‘A’ Weighting This is a function which attempts to simulate the characteristics of human hearing. See also dB(A) below.

Background The ambient noise level already present within the environment in the Noise* absence of wind farm operation.

Blade Passing The frequency at which blades pass over the tower i.e. three times Frequency* 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 This is the term that has commonly been used to express amplitude Amplitude modulation noise from wind turbines / wind farms that was not Modulation foreseen or discussed in ETSU-R-97, i.e. modulation noise greater (EAM) 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.

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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. L Aeq 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 L Aeq 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 containing a discrete frequency component most often of Noise* 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.

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

MW per No. of Hub Height Wind Farm Location Turbine model MW total Reference turbine turbines (m) 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

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Frequency comparator

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

784Hz - 1047Hz Bird calls Middle C approximate ETSU-R- typically 262Hz 82Hz - lowest 97 range for AM / 1600Hz and note of the blade swish of 800- above (male) bass 1000Hz 156Hz - 416Hz singing range Approximate range observed and measured by MAS for EAM of 160-400Hz.

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Example graph

peak The rise (peak) and fall (trough) in sound energy is dB what we refer to as The 100ms LAeq shows how the amplitude modulation and noise level is varying with time . 60 it is this change in sound level that we hear as a

trough 'thump ' / 'whoosh'. 55 The Period LAeq is a way of expressing the 'average' noise level for the time period 50 shown on the graph. If all the

the noise is. noise the time varying sound energy is taken and expressed as a 45 single unvarying value, this gives the LAeq. gives the decibel decibel the gives how loud how

axis 40 - y

The 35 level, i.e. i.e. level, The Period LA90 is the 30 background noise level for the time period shown on the graph. It is a statistical descriptor of the 23:07:30 23:07:32 23:07:33 23:07:35 23:07:37 23:07:39 23:07:40 23:07:42 23:07:44 23:07:45 23:07:47 23:07:49 23:07:50 23:07:52 23:07:54 23:07:55 23:07:57 23:07:59 23:08:01 23:08:02 23:08:04 23:08:06 23:08:07 23:08:09 23:08:11 23:08:12 23:08:14 23:08:16 23:08:18 23:08:19 23:08:21 23:08:23 23:08:24 23:08:26 23:08:28 23:08:29 noise - the quietest 10% of noise in the period.

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

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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/

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