The Bangor Hum Influence of Wind Speed and Direction on Subjectively Perceived Levels by Dr C. Barnes, Bangor Scientific and Educational Consultants November 2012

Abstract

The Hum is briefly described. A hypothesis of the Hum is advanced. Potential sources for the Hum in Bangor are discussed. Results of a study of the subjective Hum intensity as a function of wind speed and Jet Streams are presented. The most likely contributing sources to the Bangor Hum are re-evaluated in the light of the wind speed data. Competing mechanisms for human sensitivity in terms of Bragg matching and electromagnetic sensitisation are discussed. A comprehensive list of conclusions on what is known of the Hum from this and other work is given. Generally the original hypothesis is supported.

Introduction

The HUM is an annoying (magneto) acoustic effect which plagues and often ruins the lives of an estimated 2% of the World’s population. Despite 40 years research involving Defra and the UK Universities of Salford and Southampton no proper conclusions have been reached as to cause or cure for the Hum. It is thus left to private researchers the like of the UK’s John Dawes and the present author to try and elucidate this curse for the good of human kind. The Hum is often described as a quasi periodic pulsatile noise like a distance idling engine tone matched at between 30 and 80 Hz with modulations from about 1-5Hz and as being more prevalent at night and in rural or semi rural areas. Sometimes the Hum is described as difficult or impossible to screen out even with ear plugs. Following from an anomalous observation of the Hum due to car PWM electrical systems, the present author has established that besides an infrasound component, some Hums in general may have a magnetic component which enhance their perception and account for the difficulty in screening. There is also considerable body of evidence that the Hum may be related to Electricity and Power Systems. The Hum is often heard much louder inside buildings which tends to suggest that the fabric of a building somehow amplifies or resonates the Hum.

Hypothesis

The hypothesis is that the HUM cannot be purely due to a single tone of infrasonic origin, because infrasound is known to be very pervasive, so under that premise alone, many more locations should perceive the HUM. It is thus proposed multiple acoustic conditions have to be satisfied to receive/perceive the HUM.

It is also proposed that to perceive the HUM; certain precise electromagnetic conditions may have also to be fulfilled. In previous work, the author has made an observation that the HUM seems to reduce with increasing wind speed; this could be associated with moving tress and objects reducing the temporal and spatial coherence of the required sound and /or electromagnetic waves.

Bangor as a location

Besides having natural sources infrasound, to re-iterate these are; the sea, mountains and a waterfall, the author also lives close to potential sources of anthropogenic infrasound. These are; a railway tunnel, the Menai suspension bridge 1.6 km to the West, the Britannia Bridge being a combined road and rail bridge 4.25 km to the West and three wind farms, two onshore at Llyn Alaw and Amlwch about 20km to the North West and the third offshore about 30 km at North Hoyle to the North East and a pumped storage header lake some 10 km to the South East. These are all potential sources of infrasound in the region of 1-20Hz. There are also three nearby low voltage electricity sub-stations, located at OS grid references SH572718, SH 572720 and SH573721, and also a Super grid switch station 5km to the South East. The Super grid conductors run just below the mountain ridge to the North East. These are potential sources of 50 and 100 Hz sound fields and sound fields including one third and two thirds of these frequencies due to sub-harmonic generation as a result of the three phase nature of electricity supply. Finally it should be noted that there is a large gymnasium to the South –South-West of the author’s residence which is constructed with corrugated steel sides and roof. Not only could such a building act as a radio and/or acoustic reflector it could also act as a reverberant source. If this source were reverberant, this would further complicate the picture with regard to electromagnetic scattering (Lawrence and Sarabandi 2006). It is interesting to note that in most of the other local locations wherein the author has experienced loud aggressive HUMS there have been painted and or /corroded metallic structures including beach car park barrier, iron fences, power pylons and a rusty metallic barn. Recently the author has also experienced the Hum in three businesses and residential properties containing steel RSJ type girders. It is possible that some kind of passive demodulation at these structures, in addition to possible reverberation, could contribute to the perceived effects by providing in-phase audio components to stimulate the nervous system additionally. Alternatively, if the body coherently detects infrasound and an associated magnetic component maybe enhanced permeability in its neighbourhood is relevant?

Experimental

The experiment is in essence very simple but also very time consuming as it relies on the randomness of the weather to provide a suitable range of variables. The two experimental subjects are the author and his wife.

In order to attempt to elucidate the combined acoustic (infrasonic) and electromagnetic involvement in the HUM, in this present work, the author has made a painstaking and more comprehensive study of the effect of both ground level wind speed and direction on the HUM and has also examined the effects of the Jet Stream. The wind speed values in knots were recorded as were their directions. A perceived subjective HUM level averaged across the subjects was recorded on a scale of 0-10; a score of 0 representing no HUM and a score of 10 being an intolerable HUM requiring the full range of infrasound and electromagnetic ear defence. Several years’ worth of painstaking work allowed the data to be recorded and analysed. Not only can winds in association with the sea, atmospheric boundary layers and mountains generate infrasound but they can change the propagation of or mask ground level anthropogenic sources (Woodward et al 27^th Seismic Research Review) and disrupt the coherence of distant seismic sources (Withers et al 1996).

RESULTS

The results for ground level winds reveal that although the initial conclusions (Barnes (1+2)(2007) concluding that wind speed as a function of perceived HUM intensity has a simple inverse correlation may be justified. However, with more data samples now available and these having been gathered from a greater range of wind speeds and wind directions, it has been found that the correlation is far weaker than had originally been thought. Instead, a complex pattern emerges when wind direction is also taken into account. Wind blowing through appropriately sized structures, natural or anthropogenic, can generate all kinds of acoustic as well as infrasonic noises. The wind can be used to make beautiful music viz a viz the Aeolian harp.

Low level winds blowing from different directions at the author’s residence actually all have different effects on the HUM intensity. If the wind were simply reducing some external electromagnetic or acoustic coherence or both by randomly moving vegetation or metallic structures, one would perhaps have thought it might have been equally effective in all directions. However, if some wind induced, wind carried or wind attenuated sound source or sources were involved with the HUM and if the HUM hearers were located outside the immediate near fields of those sources then a pronounced wind directivity effect might be expected. An alternative is that if the building wherein the Hum is perceived is in forced or resonant vibration winds impinging on different facades of the building will also produce different effects by virtue of their directivity. Indeed this is exactly as is observed. When the wind data from different directions are plotted as sinusoidal best fits, see figures 1-5, it would appear that there are some wind speeds at which the HUM is suppressed and some wind speeds at which the HUM is enhanced, indicative perhaps of multiple processes and phase critical interactions. Reflections and standing waves associated with the structure of both the house receiving the Hum and the nearby structures are considered to be a possible cause for some of these interactions.

Of course another possibility here is that vegetation, particular nearby trees, responding to winds, do move as to reduce radio signal coherence, as previously suggested, but in doing so are responding as damped oscillators, only able to respond to certain wind speeds (Mayer 1989) and hence only able to reduce the coherence of the background radio fields at certain specific wind exposure times. Additionally, wind is also known to destroy the coherence of seismic infrasound. Withers et al (1996) have shown that winds with speeds as low 3m/s can, in certain circumstances, destroy the coherence of seismic infrasound at 15Hz and below whereas winds of greater than 8m/s were required to reduce the coherence of infrasound in the 23-55Hz frequency band. Extending the result of Withers, the author has derived a linear equation to predict how seismic frequency coherence will be lost as a function of wind speed:

F (Hz) = 0.6+4.8 W ...................................................................................(1)

Where W= wind speed in m/s.

The wind direction wherein the HUM is partly wind speed independent is North West, see figure 1. This could either be because the author’s house is located on the leeward side of a slight north west facing slope, reducing the wind’s effectiveness or perhaps because the North West wind actually contains one or because more components of the HUM are generated in or propagated from that direction. In this latter respect it is interesting to note that the nearest wind farms are located some 20 km to the North West. Also the narrow sea strait, Menai Strait is located broadly in this general direction with its two bridges as possible infrasonic sources and further along which points have been located which have given rise to daytime HUM. It is possible that the infrasound from those points gets propagated further at night. In all cases, figure 1-5 the HUM intensity is greatest at low or zero wind speed indicating the propagation of a sound source in an undisturbed night-time boundary layer as a distinct possibility and/or seismic vibration.

Alternatively, a very locally generated sound source is a possibility but this does not immediately seem to fit with the observations of the HUM at greater distances within the author’s locality, unless many such sources, the same or similar, existed and were fairly uniformly spread throughout the environment. In this respect it is interesting to note that there are electricity sub-stations and a high pressure gas main in the immediate vicinity. Such sound sources are of course relatively common throughout the urban environment

These type of data are also reminiscent of the effects obtained using radio acoustic atmospheric sounding system (RASS) particularly of the bistatic type ( Saebbo, Triad AS, Norway) with the wind blowing either across or in line with the signal field. In that case Doppler shift of the radio frequency source is measured. It may be rather fanciful to propose, but it could be rather as though humans perceiving the HUM are acting like bio-RASS systems!

Involvement of a large metallic sports hall located 130m to the South South West of the author’s residence has been cited. When motor vehicles transit travelling North Eastwards i.e. approaching from the South West along the road which runs almost parallel with this hall and towards the author’s residence on the left, the HUM ceases for several seconds. Two metres to the south and travelling in a South Westerly direction there is no difference. Therefore it is suspected then there may be a standing wave radio and/or acoustic field in this area, possibly in the form of a pyramidal volume of triangular cross-section. Such a volume could accommodate both the high and low frequencies requited for the HUM. It is interesting to note that a South West wind, figure 3, of approximately the same velocity as a moving car also kills the HUM. It is believed this must be disturbing the sound field in the standing wave volume. It is not practical to apply Doppler equations for stationary or semi-stationary fields but at these wind speeds the Doppler shift would be significant on an audio signal but is not relevant to a radio frequency signal. The maximum East wind experienced to date is about 11 knots and also looks as though it is sufficient to shift the interaction from perhaps an anti-node to a node, figure 5. The results for the other winds appear to take on a sinusoidal form with a generally increased frequency perhaps because they blow less obliquely over the zone of interaction. From the results it is very clear to see that something analogous to Bragg scattering may be happening. This is why the HUM is perceived as so intensive on some nights. Perhaps the Bragg zone does not need to be external. Effected buildings themselves could form part of it. The results figures 1 and 2 for North West and West winds are very instructive. The data have been plotted in the general form of sinusoidal fits according to the equation

Y = A + Bcos ( Cx+ D) ……………………………………………………..(1)

Table 1 below shows the coefficients of equation (1) for various wind –directions.

TABLE 1

	A	B	C	D
Wind direction

NW	5.85	2.65	1.11	-0.736
W	5.79	3.37	0.38	-0.636
SW	0.87	9.33	0.04	-0.231
S	4.19	6.04	0.138	0.214
E	6.74	5.94	0.19	0.83

Parameter ‘A’ represents the non- oscillatory constant which appears largest for a wind from an Easterly direction and smallest for a South Westerly Wind. There are mountains, power lines and waterfall to the East and a pumped storage lake to the South East. The oscillatory constant ‘B’ is largest for the South West wind confirming suspicions that there will be a scattering zone associated with the Sports Hall. An alternative explanation is that the South West wind by blowing towards the North East is destroying the coherence of an oscillatory field in that direction. One has to make the assumption that the other requisite sound and radio fields will also be somewhere in the scattering volume. The problem is far too complex to solve analytically, but reference to the angular components C and D are instructive. D is positive for cross track winds and negative for the along-track winds. Regarding the orientation of the author’s house Southerly and Easterly winds would produce least interaction with the walls but most interaction across the entire zone and this is seen particularly in the Easterly wind which is relatively free of obstruction until it reaches the zone whence it gradually, almost linearly reduces the Hum amplitude.

Clearly the standing wave field oscillates more wildly when the winds are on track with the reflection zone. A south westerly wind seems to produce a longer oscillatory period presumably because it is blowing across not only the incident and reflected path but also takes time to propagate in between. It is interesting to note that the space in between these zones as defined by the length of the sports hall and distance to the author’s residence is about 300 metres about the wavelength of a medium wave radio transmission or a 1 Hz sound wave or a 23 Hz underground seismic wave. A moving vehicle entering this zone would take five or ten seconds to transit and would disturb the fields involved with these components of the HUM accordingly. All the winds will also agitate nearby foliage which is a mechanism to attenuate and reduce the coherence of UHF radio and microwave signals. Interestingly mode conversion on this basis could give rise to the lowest pulsatile frequency of the Hum.

Returning to findings of Withers et al (1996) puts a very interesting slant on the data particularly if one assumes that all the sound fields arriving in the scattering zone are quite directional and could have their coherence ‘blown out’ by opposing winds in a manner broadly according to Withers’ findings, which have here been extrapolated across a wider range of frequency and wind speed. The relevant information after extrapolation of the wind speed from each sinusoidal plot for the first HUM ‘node’ is shown in Table 2 below;

TABLE 2

WIND	ACOUSTIC	BRAGG MATCHED Air/Water/Solid	STRONGEST POSSIBLE
DIRECTION	FREQUENCY HZ	R.F. RANGE MHZ	R.F. SOURCE

NW	8.3 HZ	3.8/.825/.25	SHORT/MED/LONG/WAVE
W	24.6 HZ	11.4/2.2/.69	SHORT/MED
SW	96.6 HZ	45/9/2.8	SHORT
S	49.56 HZ	23/4.5/1.4	SHORT/MED
E	27.7 HZ	25.9/5.1/1.56	SHORT/MED

Table 2 clearly shows most of the acoustic frequencies could be accounted for by stating that they are within the range of power line and sub-station frequencies, harmonics, and their sub-harmonics. The presence of such frequencies at the author’s residence has been independently confirmed using acoustic and magnetic spectrum analysis recording techniques.

Particularly of interest is the result for South West winds. There are electricity sub-stations to the North, the North East and South West of the author’s residence and this result shows the highest oscillatory constant (table1). It is well known that power transformers generate a fluctuating periodic component at double the power frequency fundamental with varying load (Keerthipala et al 1998), this frequency very close to 100 Hz (within the limits of experimental error) is seen in the range for SW winds (Table 2). Despite so much electronic technology in Japan, as far as the author is aware, there are no reports of the HUM in that country. Japan uses mainly underground and indoor electricity sub-stations with gas insulated transformers (Tsukao and Hasegawa 2002), presumably this minimises their experience of the HUM. It is also very interesting to note that Japan appears to take the problem of infrasound in general far more seriously than in the West.

(http://www.acoustics.org.tw/asoroc/report/Dr.%20Yamashita's%20Paper.pdf). So perhaps in this light there are simply fewer sources of infrasound available in Japan to produce acoustic beats and Bragg match with electromagnetic waves. Of course in line with the rest of the developed World, Japan has had an explosion of the latter.

In Bangor, radio frequencies capable of Bragg matching audio in the range 20-160 Hz are all available locally. There is very strong field strength from Radio Wales on 882 KHz which will be a very close Bragg match for the 8.3 Hz Hum propagated in water or the 24.6 Hz Hum component propagated in steel or rock. The Dinorwig Pumped storage plant is capable of producing such frequencies; alternatively centrifugal compressors in the gas industry can also produce noise in this frequency band. There is a Gas Pressure reduction station just to the East of the author’s residence. It is not unreasonable to expect two or more coherent wavelengths to be involved here because sound from such sources can travel through the air and underground into the walls of buildings.

Frequencies in the range around 11Hz have been associated with gas supply (Springerlink.com / index / Q6JH11813263UP67.PDF). Consideration of the Bragg matching radio frequency range is appropriate here. For airborne sound, this is predicted to lie within the Short Waves. There are no strong local sources of short waves which by day leaves only the lower frequencies in this range as possibilities. At night lower frequency short waves are returned to earth from the ionosphere. Mountain waves are also known to propagate to the ionosphere. Similarly the whole UK gas grid could be a formidable source of infrasound (New Scientist 30^th May 1992). There is no reason to suppose that with the frequencies and lengths of pipes involved this infrasound should not be capable of radiating upwards for large distances, possibly to the ionosphere (Mutschlecner and Whittaker 1990).

It has been postulated elsewhere that higher frequency radio waves might sensitise us to the Hum? To investigate associated variation in radio field strengths, a radio scanning receiver was set up at the author’s residence to elucidate variation in strengths of signals on windy and non windy days. The local 400 MHz TETRA signal varied in received signal amplitude by less than 10%. One local GSM signal hardly varied in strength at all while another one only 2 MHz away in frequency varied with deep fades up to 70% of amplitude. The local UHF TV channels transmitted from the North North East across the Menai Straits varied by very deep fades up to 90% of amplitude. The frequency of all the fades increased dramatically when it was windy or when vehicles passed by. It therefore looks as though UHF TV transmissions are also getting trapped in the scattering zone. From this result it seems that although TETRA was previously shown to be relevant in the HUM, it may simply increase the potential for the HUM rather than be the sole cause. For instance North Shore New Zealand has reported the HUM but has no TETRA (Moir 2007). The electromagnetic signals being scattered the most appear to be GSM and UHF TV. Such effects have been noticed elsewhere for TV signals (Das et al 1989) and (Sim and Warrington 2006).

An additional experiment was conducted at a number of local sites one evening when a strong Southerly wind was completely extinguishing the HUM at the author’s residence. A very weak HUM could be discerned sitting in a parked vehicle at grid reference SH 584707, despite quite a significant wind. The only point where the HUM was strong was a point much lower in town sheltered completely from the wind, grid reference SH 584725. The conclusion is that when the wind is local to the HUM hearer, it will generally, by whatever mechanism, disrupt the HUM. This supports the notion that at least part of the HUM acoustic field may not be immediately local.

To test this, a second additional experiment was carried out on a still night in a parked vehicle at location grid reference SH 589718 which is located such that the magnetic A and B components of the local TETRA transmitter will be exactly pi/2 out of phase.

To the North East of the location was a gas pressure reducing station and to the South East a low voltage sub-station. The HUM was perceived as very loud and aggressive. This location is on urban estate but there was very little vehicular movement at that time. A vehicle passing the road junction at map reference SH 590718 had the effect of deadening the HUM for some 5 seconds or so. The vehicle was travelling from North to South at approximately 40km/hr. The vehicle was to the East of the fixed HUM monitoring location. The TETRA mast was due south of both. The inference seems to be that the vehicle may have been disrupting a sound field was originating from the East, or the Tetra field from the South or both. This is similar to the conclusion reached for the non –oscillatory component of the HUM above.

Possible sound sources broadly to the East of both locations are the power grid, the mountains, the waterfall, the Pumped Storage Lake and separate electricity sub-stations and gas pressure reduction stations.

Sound could of course be reflecting off the mountains or being propagated for a significant distance in the night –time boundary layer from elsewhere. A crucial feature of the HUM seems to be that it is more easily disrupted by vehicular movement than by wind. A vehicle will readily disrupt both a sound field and an electromagnetic field, whereas the wind will have largest effect on a sound field. This seemingly confirms the present hypothesis, that both are needed for perception of the HUM. This may account for why in many rural and quiet urban areas of the world the HUM appears to ‘switch on’ late at night when vehicular movement dies down. Similarly although the night-time boundary layer starts forming after dusk it will take time to stabilise after which optimal sound transfer from a distance will occur. Daytime HUMS can probably be heard closer to the sea because the sea temperature varies less than that of the land so there is more of a stable boundary layer present for most of the time and thus less diurnal variation.

Effect of the Jet Stream

The results for Jet stream winds generally reinforce the results for ground level winds. Several significant Welsh mountains are located broadly to the East of the author’s residence. Jet Streams from directions which don’t impinge on the mountains or impinge on the windward side (same side as the author’s residence) have the effect of slightly reducing the HUM. Unless that is they are seriously kinked in shape just to the West of Britain, a sign of shear and turbulence (Smigeilski 1960 and Colson 1960), which can be its own source of infrasound. On the other hand when the author’s residence is to the lee of the Jet Stream with respect to the mountain ranges, i.e. for Jet streams approaching from broadly Easterly directions there is a slight increase in the subjective HUM level, figure 6. This is probably due to mountain infrasound generation by leeward scattering. Leeward generated winds scattered to lower levels could also however assist in the propagation of sound from any other source, simply by blowing it in the wind as it were.

Possible sounds to arrive in this manner other than mountain infrasound itself could be from the power lines, the waterfall and the pumped storage lake. In no case are the correlation coefficients high. Shearing between low and high level winds at atmospheric boundary layers is known to produce infrasound and air turbulences Smigeilski 1960 and Colson 1960).

In support of this, a positive linear correlation, figure 7, has been found between the subjective HUM intensity and intersection angles of low level winds and jet stream winds at the author’s residence but once again the correlation is poor, with a regression coefficient of only 0.31. This adds some credence to the observations of HUMS in regions with CAT not near the coast. No such regions exist in the UK sufficiently far from the coast to fully test this hypothesis. It also tends to confirm the notion that atmospheric turbulence and associated mountain infrasound has at least some, if relatively minor, part to play in the HUM at the author’s residence.

ABOVE: Figure 6 Effect of East to West flowing Jet Stream weak positive correlation with perceived HUM level.

ABOVE: Figure 7, Effect of angle between upper Jet Stream and low level wind on relative HUM intensity.

None of the Jet Stream data, from Jet stream winds in any or all directions, fitted sinusoidal equations as did the data from the plots of HUM intensity versus ground level wind speed and direction. The conclusion is that there is no Bragg Scattering taking place at Jet stream height and simply that any infrasound or turbulent effects from this height propagate to other levels where significant effect and interaction with electromagnetic waves takes place. There are few occasions when the UK is not proximal to a jet stream. However the author has noticed that when the jet stream is more than about 800 miles distant from the UK, the HUM in Bangor completely ceases with the exception of just 2 days in a 3 year observation period on which deep low pressure was in the south western approaches of the UK but no significant upper level jet stream was marked on the 300mb CRWS Jet Stream map http://squall.sfsu.edu/crws/jetstream.html. The jet stream is a source of infrasound in its own right but in the present context is the most likely driving source for mountain infrasound. Also it is known that other sounds can propagate into or through the jet stream (Chung et al 1970).

Overall, the results presented here are suggestive that HUM generation is very complex problem involving more than one infrasonic co-source in addition to the previously stated requirement for more than one electromagnetic source for enhanced perception, small wonder that no single person has completely ever elucidated the mystery of the HUM.

Discussion

The results obtained by this study are equally supportive of two possible and quite radical ideas. The first of these is that the wind at appropriate speeds in coastal mountain areas and at night can generate infrasound by interaction with mountains and atmospheric boundary and inversion layers. When infrasound of the correct frequency is produced it will scatter radio waves also of appropriate frequencies. Because the infrasound or radio frequency field in itself may also be pulsating, the Bragg type interaction which occur are manifests is perceived as the aggressive HUM. The idea being that the body can adjust to living in a radio field(s) or an infrasound field but not both, particularly if their wavelengths are comparable. Previous work, Barnes 1 and 2 (2007), has shown the magnetic components of the radio field to be most relevant. A useful analogy is to think of someone sitting in a chair. You get used to the mutual pressure and blank it out; however, if a spring bursts in the chair and stabs you in the posterior then you are instantly aware of this!

The second equally valid hypothesis is that together with a natural infrasound presence, anthropogenic sources of infrasound are also additionally and especially relevant, as they can be propagated both seismically and through night time boundary (inversion) layers and so scattered and diffracted in mountainous regions such that they too are involved in Bragg interactions with each other and /or with radio waves of appropriate frequency and similarly perceived as the HUM. It must not be forgotten that with seismic propagation in solid structures acoustic wave velocity will be very different and mode conversion can give rise to unexpected frequencies.

In other words the magnetic components of electromagnetic fields are merely the vehicles for conducting the infrasound mediated HUM into the body which to be perceived needs a very precise set of interacting and intersecting variables. These being namely the following; a source of low frequency radio emission and infrasound of comparable wavelength and a second source of higher frequency radio emission and a source of infrasound or acoustic frequency of comparable wavelength.

Given the results in Figure 2 ubiquitous 50Hz vibrations, harmonics and sub-harmonics from the power grid and electricity sub-stations are a possible source for this shorter wavelength infrasound. The prerequisite infrasonic conditions for additional, longer wavelength, lower frequency infrasound are far more likely to be met on a regular basis in coastal or mountainous regions at night. But it must not be forgotten that anthropogenic sources such as pumped storage power stations and wind turbines are often located in such regions. In a small island like Britain most natural and even anthropogenic infrasound from sources such as pumped storage power generation and wind turbines will be more or less ubiquitous, hence it will mainly be the locations and (magnetic) field strengths of transmitters and radio frequency matching aspects which will be more critical for determination of the HUM in the majority of cases except wherein locally very large amplitude anthropogenic infrasound sources are active.

Local or intense infrasound can under such circumstances reach the recipient’s body sensory organs directly, or even be conducted a vibration to the body where it could excite cavity resonances, as an aside from being modulated onto scattered electromagnetic waves causing sensory reinforcement if there is sufficient coherence of arrival. Human beings employ sensory reinforcement in everyday perception for example, reinforcement of auditory perception by sight in a noisy environment (not unlike lip-reading by a deaf person) (Burke 2001). Even the semi-circular canals or vestibular apparatus may be involved in the synergy of the senses required for HUM perception. Lebovitz (1975) has sown this organ to be sensitive to weak electromagnetic fields and is not inconsistent with the hypothesis presented here. Similarly involved in human balance, the organ contains the body’s gravity detection system. Airborne infrasound has also been shown to be associated with gravity perturbation (Saulson 1984) and so here we have yet another possible synergistic link. This is useful for it consoles the present work with the ideas of Dawes (2006). Within the vestibular apparatus of the inner ear lies the saccule which is said to contain piezoelectric material. Similarly this organ in some birds and fishes is said to contain ferromagnetic material. Birds use magnetic fields http://www.backyardnature.net/birdnavi.htmto navigate and also infrasound (Hagstrum 2001). Maybe our ability to perceive the HUM is buried deep within in our evolutionary path of development from our avian cousins.

Summary HUM factors at author’s residence

The most likely HUM factors and components at the author’s residence based on the above experiments are summarised in Table 3 below;

Table 3

SOUND	ACOUSTIC	BRAGG MATCHED	STRONGEST POSSIBLE
DIRECTION	FREQUENCY HZ AND SOURCE	R.F. RANGE MHZ	R.F. SOURCE
SE/E	GAS GRID 5-9/31 HZ UNDERGROUND SPEED 7KM/S	.125 /2.45 0.59-8.3	LONG/MEDIUM WAVE
SE	5-9 HZ Mountain infrasound/Pumped Storage Lake/Gas main	2.5-49.5	SHORT WAVE
E	24-31 HZ Gas pressure reduction station over ground SPEED 340m/s and/or Mountain/waterfall infrasound	12.2 -135-171	VHF PAGING
NE	99.5 -155 HZ Electricity sub-station	50.59-870	FM ,TETRA,TV, GSM
N/S	52-78 HZ Electricity sub-station / TETRA/ Plus Unknown acoustic source	26-56 - 293-435	FM ,TETRA
W	20-30 HZ Bridge infrasound /Menai Suspension Bridge	9.9-15.9 - 110-165	VHF PAGING
SW	29-38 HZ Bridge infrasound/ Britannia Bridge	14.4-160-210	VHF PAGING

Because the only wind speed data available is rather course data from the met office station at Valley on Anglesey, it has not been possible to search for lower ‘microbarom type’ pulse repetition frequencies as would be required by gentle HUM. What is certain is that when the frequency components which are driven by the jet stream, in all probability the mountain infrasound at frequencies between 5 and 31 Hz are not present, that is if the jet stream is absent or distant, the whole aggressive HUM often disappears. These components are Bragg Matched mainly by Low Megahertz Short Wave signals which propagate best at night and will always be present along with all the other electromagnetic signals. Thus the HUM cannot be purely electromagnetic. This observation also discounts waterfall infrasound as being the likely or main cause of the HUM in Bangor.

To reiterate, it is very instructive to consider noise from a gas main or other ground borne source travelling underground and through building structures with seismic, rather than air velocities. The longer wavelength of the sound makes a significant difference to the Bragg matching. It becomes much easier to see how long/medium wave radio broadcasts can be involved in HUM perception, see SE*/ E* Table 3.

The HUM and vehicles

It has long been known that just as with houses, the HUM is often perceived by hearers much louder inside stationary vehicles. Typical car interiors resonate between 100 -200 Hz. Vehicle suspension resonances are typically of the order of 1 or 2 Hz and other mechanical parts have resonances around 10Hz, close that of mountain infrasound. VHF, UHF and microwave radio fields can enter vehicles relatively unimpeded through window glass whereas entry of lower radio frequencies and mains frequency fields would be confined to the magnetic component, whereas the electric components would have a tendency to excite the flow of eddy currents in the vehicle body. Furthermore vehicle electrical systems use PWM control which can generate EM fields even when the vehicle is stationary. Vibration of the vehicle structure at eddy current frequencies may be another mechanism by which vehicles amplify the HUM especially when the vehicle is parked under power lines. It is known that the magnetic components of electromagnetic field are most crucial for the HUM ( Barnes 1 and 2 (2007)) and this is borne out by people who still perceive the HUM in Faraday tents (Moir 2006) or in Faraday cages (Dawes 20076) wherein the electric component will be cancelled.

The HUM and electricity supply phases

Some mobile experiments were conducted at very rural locations outside Bangor where only one electricity supply phase was present in the form of overhead low voltage cables. Generally the HUM was not heard in a car at these locations even though the higher frequency electromagnetic pre-requisites were fulfilled. Only where three phase electricity supply was present then the HUM was heard. It would seem then criteria for the HUM is not only the electricity supply frequency but that it be present in three phases separated by 120 degrees. This will generate periodic electromagnetic and acoustic signals at mains frequencies and harmonic and sub-harmonic frequencies. 16, 33, 50, 66, 100 and 133 Hz etc. The hypothesis being, the more frequencies present, the more chance of Bragg matched beat frequency conditions and /or direct interaction with Mountain Infrasound. .

Concerned with power line electromagnetic sources, the author has for several years been observing the behaviour of the local ELF spectrum with respect to power line harmonics with a piece of computer software known as Spectrum Lab. These harmonics often appear to vary in relative intensity during HUM episodes. The author has also reported elsewhere on their behaviour with special reference to the weather, space weather and the HUM. Also a very strong and unusual ELF signal between 1.08 and 1.24 Hz often centred on 1.13 Hz sometimes appears to prevalent at the author’s house. Signals at 2.4, 5 and 7 Hz have also been observed. It is not yet known if these are of relevance to aggressive HUMS. However, during the period of writing, these frequencies could also be detected in the received and de-modulated audio spectrum of a least four different ionospheric heater signals ranging from 2.3 -6.9 MHz. Based on the frequency ranges involved, it is suspected these signals may be arising from EISCAT or similar. There remains a conjecture by some that ionospheric heating is a cause of or at least a contributing factor of the HUM. Soviet and European experiments on such heating certainly began about the same time major HUM reports in Britain commenced and continue to this day , see Ponomarev and Eruschenkov (1977), Karashthin et al (1977) and Rapoport et al (2003). Russian Scientists have recently succeeded in propagating artificial ULF signals over a distance of 1500 km (Bolyaev et al 2004). This starts to become significant as far as parts of the UK are concerned. Certainly in the light of this and the requirement for Bragg radio frequencies in the low MHz range to satisfy one of the HUM components at the author’s residence these ideas may be worth pursuing further. Another mechanism for these signals could be by mode conversion in piezo-electric or magneto-strictive rock.

Conclusions from this and other work of the author

The author believes this work now comes close to a solution to the perplexing problem of accounting for the generation and perception of the HUM. The ultimate solution will, perhaps, only come when Science has a far better understanding of infrasound, atmospheric and seismic and electromagnetic wave-wave interactions. The following list of points is now more certain

· One of the most comprehensive pictures of a Taos type HUM to date has so far been presented.

· The work strongly supports the hypothesis that the HUM is a magneto-acoustic effect which requires a complex combination of electromagnetic frequencies and appropriate infrasonic cofactors for its perception.

· The HUM may be conducted into the human body at the right ear in some individuals. Electromagnetic signals present may be may be the facilitators for enhanced sensitivity of the body to infrasound

· The HUM might involve longitudinal electro-scalar waves

· The HUM appears to be enhanced when infrasound and electromagnetic atmospheric waves are of similar wavelength (equally matched to within an order of magnitude of each other depending on scattering angle and volume) causing Bragg reflection (scattering) of an electromagnetic component(s)

· In some cases local infrasound may enter the body at other places and act as to coherently reinforce the Bragg scattered electromagnetic radiation by duelling of the senses i.e. optical modulation or vibration of body cavities

· The said infrasonic sources can be natural or anthropogenic but must be present sufficiently and with appropriate frequencies to account for the geographic distribution and temporal occurrence of the HUM

· A strong radio transmission in the hundreds of kilohertz radio frequency range or low megahertz range is often associated with sensitisation to the HUM.

· A second strong radio transmission in the VHF,UHF or microwave region with critical phase matching in the propagation delay between its magnetic potential A and magnetic field vector B might a pre-requisite for the HUM .

· The most likely natural infrasound sources are microbaroms, surf noise and mountain infrasound. Mountain infrasound is driven by the jet stream and the aggressive version of the HUM sometimes disappears if the latter is not proximal

· The most likely anthropogenic sound sources are the electricity power and gas grids and bridges, not forgetting the possibility of wind turbines; acoustic noise and LES waves from the electricity grid are perhaps the most ubiquitous of these followed by noise from the gas grid.

· The HUM does not take on the direct modulation envelope of any of the radio transmitters involved because as coherent detectors, humans require coherence times to respond to signals which outweigh rapid modulation periods.

· The perceived HUM is more aggressive in mountainous areas probably due to involvement of mountain generated turbulence and associated waves.

· The perceived HUM level seems to get more aggressive with increasing numbers of competing radio and /or anthropogenic infrasound sources and increased radio passive inter-modulation products. Clearly the possibility for acoustic beats also increases here.

· Standing wave fields can accentuate the HUM intensity and directivity.

Acknowledgements

The author wishes to acknowledge the aid of his wife Gwyneth as valuable experimental assistant and with whose infinite patience the preparation of this work and manuscript was possible.

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