Wind farms with OAM, the major source, amongst renewables, of infrasound which leads to the contemporary world LFN phenomenon known as the Hum? By Dr Chris Barnes, Bangor Scientific and Educational Consultants, e-mail firstname.lastname@example.org. First published on Internet 06/05/2014.
Dr Barnes Homepage http://www.drchrisbarnes.co.uk
A distinction between the LFN and the Hum is drawn. The Hum is briefly described and reviewed. A strong case is presented for the involvement of infrasound from Wind farms exhibiting OAM (other amplitude modulation), as being a major cause of contemporary world Hums is presented. Far more people may be affected than previously thought when independently proven infrasound ducting and amplification mechanisms are taken into account. Surprisingly 80% of affected people live in-between 25-41 km from a wind farm, such distances hitherto considered to be safe. When wind farms emit OAM they are also most electrically unstable and hence secondary Hums as a result of power systems infrastructure especially transformers and reactive compensators and any synchronously connected systems such as gas compressors, water and sewage pumps etc., may also feature. Power systems due to their sheer energy density are implicitly coupled with the entire lithosphere - atmosphere system via geological and space physics processes and this intimacy results in the Hum also have seismic, magnetic and electric components to which some individuals might also be sensitive. As previously concluded elsewhere, the Hum is far more than just a noise. The industry is presently looking a design solution to eliminate or minimise OAM. It is hoped by the present author for the sake of humanity that future developers will find sufficient funding to also build infrasound reduction solutions into all newly built farms and retrofit some existing ones. Because power systems instability often occurs as an adjunct to the turbulence which brings about OAM solutions to this too need to be sought both from the point of view of protecting power systems infrastructure and connected equipment and from the point of view of eliminating or reducing secondary Hums and vibration. The view taken by the present author is it is essential to reduce impulsive airborne infrasound transmission form wind turbines and wind farms because of the damage and misery caused to people's lives and health, particularly as such impulsive signals have the ability to excite secondary resonances at other frequencies within even distant buildings. This point has been muted previously by the present author and is also highlighted in NASA technical paper 3057, see Hubbard and Shepherd 1990 .
Renewable energy in general has recently been suggested to be a major cause of the LFN phenomenon commonly referred to as the Hum [1-3]. Renewable energy can cause the Hum for three main reasons: firstly because of direct infrasound and seismic radiation; secondly because of indirect infrasound, seismic and electromagnetic radiation from power systems equipment and the seismo-acoustic response of any secondary motors, fans, pumps etc. connected thereto to poor power quality and power systems oscillations  and acoustic emissions are a problem with any adjustable speed drive equipment under poor power quality . Thirdly, interference with lithosphere, atmospheric and space physics processes, see Barnes [6, 7].
Now the wind energy industry (December 2013) has acknowledged and wants to solve OAM ( other amplitude modulation) [8 ] the question is posed here, are Wind farms, via the medium and long range propagation of infrasound and/or the generation of secondary infrasonic and seismic effects, the cause of potentially far worse LFN problems and ‘mystery Hums’ than previously given credit?
The main distinction between LFN and the so called ‘Hum’ has always been that LFN, being usually local, is traceable. The Hum on the other hand has often been shrouded in mystery and perhaps mainly because of the untraceable and historic Taos Hum  has relegated by some to the realms of pseudo-science. The Taos Hum and early UK Hums was most likely untraceable because infrasound as a potential cause was not considered at the time. The Hum is both temporal sporadic and geo-sporadic, although some claim to perceive it louder at night. Generally the Hum seems to be strongly amplified by buildings perhaps by resonant modes of pipes and chimneys  and rooms . Those afflicted by the Hum perceive a quasi - periodic engine like noise which has sometimes been tone matched to between 30-80 Hz by musically oriented hearers and which is also perceived as being periodically modulated at about 1-5 Hz. Some also feel pressure or popping in the ears, are awaked from their sleep by the phenomena and find ear plugs fairly ineffective. Others experience the phenomenon in only one ear. Such phenomena are clearly not tinnitus because two affected individuals in the same house have been able to describe the same Hum pattern, for instance the present author and his wife. Prima fascia the subjective properties described by most individuals afflicted by the Hum are mainly those of infrasound, see Barnes  and Salt . As sound frequency drops below 30 Hz, most individual’s tonal perception is in fact lost and upon private laboratory testing of three individuals by the present author, some conceive downward ramping frequency below 30 Hz actually to be rising whilst in reality it is falling. This type of phenomenon if general could account for both the tone matching description outlined above and acoustic researcher’s inability to audio record the original Taos Hum. If the infrasonic frequency falls low enough and the waveform is impulsive enough then individual cycles can be perceived. However, in order to fully account for all of the anecdotally reported qualities of absolutely all Hums one reaches the conclusion that the Hum may be in fact far more than just a noise  and that magneto and or electro-acoustic phenomena may be involved in both generation ) and perception . Magnetic receptors have been proven to be essential in bird navigation  and are disrupted by radio emissions . More recently they have been shown to influence alignment and grazing manners in even higher mammals  and are disrupted by electrical power line fields, see Burda et al (2009)  and have been found in human tissue . It is hypothesised here that infrasound may further sensitise such detection in humans hence adding to the misery of the Hum. Some have even advocated magnetite involvement in human memory [19, 20] while previous work of the author has shown a link between unstable power grids (such instability brought on by wind farms) and anomalous geomagnetic behaviour [6, 7].
A notable historic Hum frequency 0.3-10 Hz, see Garces et al  which has been traced to infrasound is the Volcanic Hum of Hawaii. Volcanoes emit considerable acoustic power, sometimes as large as 10^7Watt, see Fee et al (2010)  this being radiated mainly vertically upwards into the atmosphere but also seismically. The Kokomo Hum of Indiana was traced to a harmonically related mix of industrial infrasound and industrial acoustic sound involving compressors and fans, see Cowan (2008) . When the sources were muted, a few people carried on perceiving Hum-like noises which was unexplained at the time. One of the first notable British Hums was the so-called Bristol Hum. It has recently been disclosed that this was traced to a large industrial fan on the Shell site at Avonmouth and that the Hum disappeared when the site was closed . Recently a new Bristol Hum has surfaced and is thought by some due to chronology to be related to the newly commissioned wind farm in Avonmouth . Wind farms, particularly those with modern large, more slowly turning turbines are capable of generating infrasound which has been shown to travel up to 10km under certain conditions . Elephant behaviour depends on their use of infrasound for communication and recent studies of this highlight the fact that even ground level generated infrasound in general can travel once it becomes airborne under appropriate weather conditions and at appropriate times of day and night see Garstang et al, . Following such logic, indeed it has been recently recognised that wind farms can cause infrasound over extended periods of time in England and Germany (Haak 2007). This is perhaps hardly surprising in the UK, which already has 1774 active wind turbines spread between 139 separate wind farms (BWEA 2007). Furthermore, infrasound not only travels through the atmosphere but also couples to the solid earth as air-coupled Rayleigh wave or ground-coupled air wave. In this case, the propagation velocity of Rayleigh waves approaches the sound speed. Furthermore the approximately 1Hz infrasound associated with these farms could be more of a problem than previously thought because it can modulate onto higher frequency sound creating a pulsating or periodic field. This in a sense could be the pulsating modulation of some people’s Hum? Some 70% of locations, world-wide, which report the Hum are close to wind farms. Possibly an even greater figure than this is indicated in Britain which has Hum reports arising from Scotland, Wales, Cornwall, Gloucestershire, Parts of Northern England and Parts of the English South Coast all often being within a few tens of kilometres of wind farms. Differentiation however between a Hum based on noise entirely from Wind Power or Hydro-power may be difficult on a geographical basis because many of the sites almost co-exist, see http://www.r-p-a.org.uk/content/images/articles/1/BWind.JPG and http://www.r-p-a.org.uk/content/images/articles/1/hydro.JPG. It will be shown in this present work that wind is, in fact, a perfectly plausible assumption for both the new Bristol Hum and many cotemporary world hums.
Throughout recent history all sorts of sources have been blamed for the Hum. These include multiple aspects of electrical power systems , motorways and gas mains, see Krylov 1997  railways , aircraft , sewage and water pumping , ships at sea , mating Toad fishes  etc., etc. Assuming the use of synchronous equipment there will almost always be links between electrical power systems railway equipment, gas compressor equipment and sewage and water pumping equipment and thus the mains driving waveform may be crucial in describing the electrical and mechanical behaviour of connected and inter-related systems capable of generating noise and vibrations. Because until recently Hums appeared to be limited to the developed Western World, some had even suggested that they best correlate in space-time with military communications aircraft .
At least with regard to the Hum experienced in Bangor, North Wales, the present author has showed it has an association with electrical power generation, particularly with respect to infrasound received at his house which seems to coincide with the use of certain specific combinations of motor-generator sets at the Dinorwig pumped storage power plant  yet peculiarly on some occasions a similar frequency infrasound component seems to depend on domestic water pressure in the house . Although at first sight unlikely, it is believed that the two infrasound conditions can in fact be rationalised. It is known that although the Bangor water supply is gravity fed, there are University tower buildings close to the author’s residence which employ their own mini-pumping station. Assuming the use of mains synchronous pumps, a complex relationship with pressure and the mains driving waveform might exist? North Wales is also served by a number of wind farms on Anglesey and offshore (North Hoyle). The amount of power fed into the grid from these too will influence the choice of pumping and generation at Dinorwig. The present author has also shown that when more wind power is in use in the whole of Britain per se, there is more instability, sub harmonic, harmonic and inter-harmonic present on the super-grid double circuit on either side of the Pentir switch station  and has since been approved by Ofgen for renewal . Power grids the world over may contribute to the Hum by very complex geophysical processes or alternatively their bad behaviour may be merely symptomatic of wind power causing electrical disturbances whilst simultaneously being a more direct cause of the Hum by radiation of atmospheric infrasound. Given the quasi coherent magneto-acoustic signals occasionally received at the author’s location both containing Hum frequencies it would seem both scenarios are quite possible.
Wind farms with OAM, the strong case for their involvement as a major Hum source.
Until recently there were no recorded outbreaks of the Hum in Russia or China. This led to some credence for the above military communications hypothesis . Radio signals, however, do not respect borders and this fact together with the fact that the Hum is not necessarily experienced adjacent to large VLF transmitters seems somewhat to diminish radio frequency hypotheses of the Hum. In all other respects these countries have similar infrastructure to the West. The main difference is they have taken longer in adopting and implementing renewable energy systems. The Hum is now a feature of virtually every continent on earth which has such systems. Close inspection of recording mapping visits to websites set up for those concerned about or experiencing the Hum show almost 100% geo-spatial correlation with sites of renewable energy production , in which case the mechanisms will be expected to be similar to those experienced with the Bangor Hum.
NAM (normal amplitude modulation) is the condition which causes the ‘swish’ noise of wind turbine blades, see Smith et al 2012 and annoyance to those living nearby such turbines. On the other hand OAM (so called ‘other amplitude modulation’) occurs sporadically for wind farms experiencing sudden changes in wind speed and direction. The noise created is a far more penetrating and impulsive sound. Although the peak frequencies during OAM are of the order of 300 Hz (ref) and would not propagate far, the noise is described by other experts as deeper pitched than blade swish and the accompanying infrasound has been reported to cause disturbance and potential physical harm to people living up to several kilometres away from wind farms. The industry are presently looking a design solutions to eliminate or minimise OAM [40,41] but give little or no attention to infrasound as it is wrongly believed it does no harm to people. However, vibro-acoustic disease is a proven and grave condition . Such solutions for OAM are a step in the right direction and it is hoped by the present author for the sake of humanity that future developers will find sufficient funding to build infrasound reduction solutions into all newly built farms and retrofit some existing ones. Because OAM is impulsive it will contain the blade crossing frequency and harmonics together with other lower and higher frequencies. It used to be thought that individual turbines would exhibit OAM in a manner not related to other turbines in a wind farm. However, it has recently been shown that OAM can occur in a summative manner across an entire farm and moreover creates summative electrical disturbances as well . The description of the temporal and geographic behaviour of OAM is strikingly similar to that of the Hum in that it can sporadically appear and disappear. It can occur for periods of anything from several minutes to several days or even weeks and it is prevalent at night. Since OAM is associated with wind shear and turbulent low level jets also prevalent at night, see Bass (2012)  and since turbulence causes a coherence across different turbines on any given farm which in turn causes power output fluctuations, see Sorensen et al , then OAM is probably a very good and symbolic indicator of general wind farm instability from both an infrasound and electrical perspective.
The author lives approximately 25km from four wind farms as the crow flies. Given the stated decibel levels for OAM one would not under normal conditions expect OAM or infrasound to propagate so far. However, the wind industry does not take into account additional infrasound ducting [46,47] and atmospheric amplification. Amplification of infrasound can take place at various heights in the atmosphere including the troposphere in stratified boundary layers ( see Naugolnykh 2009)  and in supersaturated water vapour, see Naugolnykh and Rybak (2008) . Infrasound amplification can also take place in the Stratosphere and the ionosphere . Nor do such models take into account the effect of surface topography, particularly mountains . Indeed the very behaviour of a wind farm to the wind itself is rather like that of a mountain range and can even alter rainfall and temperatures [52, 53].
Taking ducting and atmospheric amplification into account would give infrasonic Hum due to wind farms considerable range and geographic spheres of influence and could well mean, for instance that the Bangor Hum and other similar hums need re-evaluating. Although power system related, wind turbines rather than hydro turbines might, for example in Bangor, conceivably be the prime mover. The latter hydro-turbines may nevertheless exhibit added instability as a result of wind integration and nothing detracts from the fact that seismic noise can propagate from such installations. In any event, the Hum remains far more than just a simple noise . Both types of turbines, their infrasound, their electrical disturbance, power-systems and the lithosphere –atmosphere- near earth space system and solar weather remain intimately and inexorably connected.
Even if one takes a very simple view of the Hum as just infrasound, which does not fit all the observed facts but may account for a substantial majority of cases one then must ask the questions what damage could infrasound do and how many people might be affected. Although only an estimated 2-11% of people world- wide perceive Hums we need to ask the question are those who don’t also affected in any way. Very disturbingly, Salt and Hullar (2010)  discuss the physiology of the ear and the raise the possibility that wind turbine infrasound, of which OAM can be considered an extreme form, can influence and permanently alter the physiology of the ear whether or not it is heard. Sensitisation of the ear to infrasound and LFN has also been discussed elsewhere, see Oud , 56]. Aural sensitisation by digital communications technology may conceivably also augment rather than cause the Hum, see Barnes .
In Britain most wind farms are located in fairly rural areas of Scotland, the West Country Wales and Northern England but there are also offshore farms closer to larger population areas in Eastern and Southern England. The Hum has been reported in all of these UK localities and there are both high profile reports where the particular Hum has taken on the name of the locality such as for example, but not exclusively; Largs, Bangor, Llanidloes, Swanage, Sudbury, Loch Ness, North Shore (NZ), Windsor (Canada), Kerry, Ireland etc. and there are lesser known Hums which can only be located by careful application of internet search criteria. The author has previously reported on changes in UK Hum distribution on the basis of altered power flows when certain conventional and nuclear power stations have closed . In the light of the above it is very pertinent to state that not only would there have been altered power flows but also altered amounts of wind generation needed on stream after such closures. Even if new Hums are limited to directly propagating atmospheric infrasound, potentially over a million or so people in Britain might be affected.
However, one must also take into account the secondary effect of wind farms causing poor power quality especially when experiencing OAM. This in turn will inject sub-harmonics and inter-harmonics into every part of the electricity distribution network and could result in secondary Hum like effects emanating from sub-station transformers and any synchronous electrical machines. A case of the former has been investigated and reported on by the author elsewhere . In addition to pumped storage systems, wind farms are now been shown to provide huge inter area oscillations, see Brownlees (2007), who discuss the effect of wind farms on the Irish Power System. .
Perhaps then not surprisingly, the present author has shown contemporary Hums to be more or less exclusively limited to parts of the world where renewable energy systems are employed. In this respect it is interesting to note that prior to the advent of wind power, China and large parts of Russia and the former Soviet republics had no Hum reports at all.
If one takes secondary Hum generation into account and potential Hum generation by the earth -space system as well, then possibly eventually no one on the planet will eventually be immune. Only time will tell on the biological implications of this.
It is highly instructive to compare the cumulative number of high profile press reported Hum cases in the UK with installed wind power in the period 2007-2012, see below:
A striking positive correlation, R=.97 can be seen.
The above result represents only high profile cases. If one does more careful internet searching using such search terms as: ‘The Hum’, ‘Buzzing at Night’ ‘Unexplained Low Frequency Noise’, ‘Pulsating noise’ etc., the one can find literally thousands of local media and discussion forum entries. If one then adds names of virtually any villages and towns within even up to 40km of any UK wind farm one is almost guaranteed to find reference to the LFN symptoms commonly associated with the Hum.
Analysis of the distances of complainants to wind farms has been made by the present author using postcodes. Surprisingly 80% of those experiencing the Hum live at distances in-between 25-41 km from a wind farm. 12% live at 13km from a wind farm and the remaining 8% live 6 km from a wind farm. The UTLS is on average between 10-18 Km in height. The author has previously noted an association of the Hum with the position of the jet stream where jet stream cirrus at UTLS height is visible. This result is in very strong support of the notions of infrasound propagation and amplification as described above. Further undeniable and independent confirmation of the author’s hypothesis is provided by Waxler and Blom (2009)  who state that ‘Infrasound can propagate to ranges of many hundreds of km. Signals received on the ground at ranges of 200 km or more have propagated high into the atmosphere through the stratosphere and thermosphere. At shorter ranges, the propagation is dominated by structure in the lower atmosphere such as the jet stream and the atmospheric boundary layer.’ The distribution of Hum complaints might be explainable as follows: most wind farms are in very rural locations and people living nearby have been known to have settled cases out of court for very large amounts . Alternatively they simply live too close to suffer night-time diffraction effects due to wind shear.
In the meantime, it is highly encouraging that the wind industry has recognised OAM which is at least one small part of this highly complex problem which is the Hum. Much more however, obviously needs to be done. Infrasound and second order effects on power systems and our ionosphere now need to be addressed. The author remains available as a consultant for any parties interested in this and similar fields.
Although there are a few high profile cases of Hums which predate wind technology, they have been limited and not world- wide. Only since the advent of wind power are Hums been reported almost world –wide. Previous earlier Hums which have been readily traced have either been due natural processes such as volcanism or due to the interaction of sound fields from multiple sources. Occasionally off-balance industrial fans and the like have been to blame. Under the impression of inter and intra-area power oscillations, harmonics, inter and sub-harmonic any and all mains synchronous equipment will inherently become more acoustically noisy and behave as though it were ‘off balance’, thus increasing the chances of experiencing industrial and domestic Hums. Such signals are far more likely in countries which employ a lot of renewable energy. So although infrasound is not the only source, such arising from wind farms undergoing impulsive OAM has been shown here to be a strong potential candidate for contemporary and ever increasing cases of the Hum the world over. Its spatial coverage could be far more than had been previously suggested and thus far more people may be affected than previously thought when atmospheric ducting and amplification mechanisms are taken into account.
When wind farms emit OAM they are also most electrically unstable and hence secondary Hums as a result of power systems infrastructure especially transformers and reactive compensators and any synchronously connected systems such as gas compressors, water and sewage pumps etc., may also feature.
Power systems due to their sheer energy density are implicitly coupled with the entire lithosphere - atmosphere system via geological and space physics processes and this intimacy results in the Hum also having magnetic, seismic and electric components to which some individuals might also be sensitive. As previously concluded elsewhere, the Hum is far more than just a noise. It is encouraging to note that the wind industry wish to address the problem of OAM and to some extent addressing this will reduce both primary Hum due to airborne infrasound propagation form the turbines themselves and also secondary Hum arising as a result of power system disturbances. However while ever renewable energy and PWM systems are used there will remain stronger potential for Hums of a secondary nature. The government too have expressed a desire to slow down wind farm development if local populations are opposed to it, see Spalding Guardian . The view taken by the present author is it is essential to reduce impulsive airborne infrasound transmission from wind turbines and wind farms because of the damage and misery caused to people's lives and health, particularly as such impulsive signals have the ability to excite secondary resonances at other frequencies within even distant buildings up to 40km from major wind farms. This point has been muted previously by the present author and is also highlighted in NASA technical paper 3057, see Hubbard and Shepherd 1990 . Independent evidence that wind turbine infrasound can propagate up to 60 km has recently been provided in a prestigious Meteorological Journal by the 2011 CASA Infrasound Field Experiment, see Pepyne and Klaiber, 2012 ams.confex.com .
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