Propagation of Low Frequency Noise

This article contains information on the Propagation and Measurement of Low Frequency Noise (LFN) and Infrasound (ILFN)

LFN can travel considerable distances and still affect peoples' health. Because wind farms are typically sited on the tops of hills and mountains LFN emitted by wind farms has no barriers and can travel considerable distances, depending on wind direction, atmospheric conditions and local topography.

Higher-frequency noise is less of a problem, except to those people unfortunate enough to live in hearing range of a wind farm. The atmosphere filters out higher-frequency noise so it doesn't carry nearly as far.

Based on the personal experience of some members of this group there is very good reason to postulate that LFN emitted by large wind turbines can travel at least 30 miles. Due to the omnipresent nature of low-frequency noise, its source is extremely difficult (if not impossible) to pinpoint, so proving our hypothesis would be very difficult. However, we do have seven years of observations so we are as certain as possible that this hypothesis is correct and would like the opportunity to prove it in due course. Below is a graph produced from a noise recording in a rural Carmarthenshire home in June 2009 before Alltwalis wind farm was built. See attached graph: EG noise graph.jpg

Before elaborating on the propagation of LFN a bit of background in noise impact assessment requirements for wind farm applications is useful.

Measurement of Wind Farm Noise

Noise measurement guidelines, ETSU-R/97, were drawn up in the 1990s in collaboration between wind industry experts and government bodies. These guidelines were drawn up specifically to monitor and assess the potential impact of wind farms on local residents. At this time wind turbines were much smaller, and the low-frequency noise spectrum was much smaller.

The ETSU-R/97 guidelines only require the wind farm developers to monitor and assess potential noise emissions using an A-weighted filter (dBA), which was developed in the 1930s when noise monitoring equipment was less sophisticated. The A-weighted filter is designed to detect what the ears normally hear. This filter effectively removes nearly all the low-frequency component of the noise (LFN), and all the very low frequencies (ILFN).

As wind turbines get larger, the LFN and ILFN spectrum of the wind farm noise gets greater. The end result is that wind farm noise predictions effectively ignore the largest portion of the noise spectrum. The result is that wind farm applications cannot fail on the basis of noise 'predictions'.

Another point on noise prediction models used by the wind industry is that they assume spherical projection of noise from the turbines. As you will see below, this is a very idealised assumption, which reduces the predicted noise output.

Factors Affecting Low-Frequency Noise Propagation

  • Normal mathematical models for predicting noise levels do not apply very well to LFN.
  • Atmospheric factors can influence how far LFN can travel (most noise impact studies only assume spherical spreading of sound):

o Topographical Effects

Sloping land with increasing ground angles, especially in combination with atmospheric conditions, can cause sounds to combine (e.g. near Vancouver Airport, hills rising from a flat plain caused sound levels to be 20dB higher at 5500m than at 4000m).

o Atmospheric Effects:

During the day warming air rises, increasing turbulence and carrying noise aloft, scattering wind turbine noise.

The following factors can also affect LFN:

§ Stable night time atmosphere

At night there is normally minimal atmospheric turbulence and light winds. These factors enable noise from wind turbines to carry much farther than expected.

§ Inversion layers

When a temperature inversion layer forms above the height of turbines, it can reflect some of the sound back toward the ground and, with the ground, create a channel to facilitate longer-range transmission of sound.

Other factors can affect LFN readings

o Coherence

Coherence is interference patterns of noise from a cluster of wind turbines. For example, if you drop two pebbles at different spots in a pond, you would produce a chaotic pattern of ripples wave peaks combining, troughs combining, or even a wave and trough cancelling each other out. The same principles apply to sound waves in air.

o Resonance

Amplification of LFN inside an enclosed space, e.g. a house. The graph below shows simultaneous indoor and outdoor noise recordings at a house near Shirley Wind Farm, USA. Between the frequencies 14 and 28 Hz, the noise indoors is up to 20 dB higher, which is caused by the house resonating and amplifying the noise - like putting a vibrating tuning fork on a piano. See attached graph: Shirley WF LFN resonance.jpg

QUICK LINKS

mlag blog | latest posts
Feb 26, 2016
Don't forget objections have to be with the Planning Inspector by 2nd March - that is next Wednesday!
Feb 9, 2016

Seren has lodged an appeal for this turbine at Ffrwd which was refused by Ceredigion Council in 2015.

Help for you about the main points to make to the Planning Inspector on our link:

Ffrwd Farm, Llanwnnen, Lampeter

Deadline for letters 2nd March 2016.

These should add further comments or modifications to any original objections. By email to: 'wales@pins.gsi.gov.uk'.

Jan 25, 2016
Some good news! Seren's appeal against the Carmarthenshire County Council's refusal of their 74m wind turbine at Blaen Pibwr - near the Botanic Gardens - has been dismissed.


 
 
 
Oct 28, 2015
Objections required AGAIN! Seren have appealed the Blaen Pibwr development.
Aug 25, 2015
A Community Councillor has been called to resign over breaches of the code of conduct.
Aug 24, 2015

We have put on another web page -  Legal / Procedural Challenges.

This page is under construction so more to come!

Aug 23, 2015

Have a look at our new web page: Recent Planning Decisions.

Other recent Planning Decisions

 

Aug 23, 2015
Nothing has been decided yet on the re-application for a turbine at Maescadog. Your objections can still help - of special importance are transport issues of the turbine to the site and new regulations about bats requiring more detailed monitoring. There are many species of bats roosting at the nearby Dolaucothi Gold Mines.
Jul 9, 2015

Proformas for Objection Letters are available to download by clicking here for people who have NOT objected before

And here for a different proforma, worded as though you have objected before

You can print, add your comments, sign and post
OR copy content into an email amending to reflect your views and send via email

Deadline is Wed July 15 2015

Jul 2, 2015
We need to act now! Another application has been made for a turbine at Maescadog, Caio. The previous application was refused by CCC AND at Appeal. Previous objections will not count so could you write again using the new application number? The turbine is at the same site and is the same size so look below for what to do now. You could resubmit your previous objection or do a new one.There were over 200 objections previously - yours matters this time too! Time is short so please get a letter in by 17th July. Click on this blog to see the information you might need for your objection.
Mar 28, 2015
A German company, Energiekontor, wants to erect two industrial scale wind turbines on Mynydd Pencarreg.
Feb 13, 2015

If you have recently bought a house in the county you could help us gather information.

Did any wind turbine applications situated in the vicinity of the house you bought show up during the conveyancing process?

Did the searches show proposed or applied for wind turbine developments that might impact on your house? These include council searches or the declaration by the seller.

We want to encourage the Law Society to improve their forms and solicitors to offer more extensive searches.

Nov 5, 2014

Public exhibition for wind farm on Mynydd Pencarreg, Rhydcymerau

Jun 11, 2014
Refusal for Application E28824
May 7, 2014
News is just in that the Appeal against the decision by Carmarthenshire County Council, in December 2012, to refuse permission for 21 wind turbines on Llanllwni Mountain has failed.
Mar 27, 2014
April 3rd is the deadline for objections to: E/29773

Land at Panteg, Cellan, Lampeter Carmarthenshire, SA48 8HN

 

Mar 21, 2014

What we thought has now been proven! Walkers and climbers turn their backs on Scotland as electricity companies industrialise wild lands, according to a new survey by the Mountaineering Council of Scotland (MCofS).

 

Mar 21, 2014
Alex Salmond is not only recommending Scottish independence. His love of wind farms has cost tax payers a huge amount of £ since the SNP took power.Will Scotland be able to afford that if independent, I wonder?
Mar 14, 2014
On 20 Jan 2014 Kris Hopkins,Under-Secretary of State for Communities and Local Government, responded to a question about the culmulative visual impact of wind turbines in Lincolnshire.
Mar 5, 2014
Wind Farm developments scrapped!
Feb 7, 2014
Easy access to see planning applications for wind tubines in Carmarthenshire.
Feb 7, 2014
Wind turbine rotor blades are difficult to recycle says a report from Aberdeenshire Council's Garioch area planning committee.
Jan 29, 2014
European Court of Justice condemns EPAW
Jan 26, 2014
Well we knew it! Wind turbines will take thousands off the value of your home says a report in the Daily Mail.
Jan 26, 2014
Wow! Taking turbines down because they spoil the view!
Local Planning Applications
Applications are flooding in, all over our county. For further information on Carmarthenshire Planning Applications (lists & maps) please click here

Mynydd Llansadwrn Action Group
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Current Local Planning Concerns:
Rhydcymerau / Bryn Dafydd:
Single wind turbine, 86.5 metres (283ft) tall.
Rhydcymerau / Pencarreg:
2 wind turbines, 100 metres, 328 ft tall.

For further information on Carmarthenshire Planning Applications (lists & maps) please click here.

Planning & Objections
Addresses for objections to Wind Turbine developments in Carmarthenshire are:
planningconsultations@carmarthenshire.gov.uk Planning Services, Civic Offices, Crescent Road, Llandeilo, SA19 6HW
Need further info? Please click here