Completing the Jigsaw : How mains earthing (grounding) systems and the latest brain and hearing research yields up the final secret of the Hum as a whole electro-magneto-acoustic phenomenon rather than just simple LFN. By Dr Chris Barnes, Bangor Scientific and Educational Consultants, Bangor, Gwynedd, Wales, LL57 2TW. E-mail email@example.com
A brief history and geography of the LFN phenomena known as the Hum is discussed. ELF Electromagnetic anomalies have been noted at the sites of some of the original U.S. Hum cases. The recently discovered notion that Hum maximises in countries with both renewable energy and T-N, especially PME earthing systems with additional water and gas pipe ground currents is re-visited. Evidence for magneto-acoustic and electro-acoustic mechanisms of Hum perception is discussed from both a first- hand experimental evidence experience point of view and a review of possibilities from brain and audition research papers. The present work strongly suggests the notion that PME earthing systems, brain and audition research can yield up secrets of the Hum. All three branches of the evidence considered produce elements of corroborating information. There is far more evidence for the Hum being a purely magneto-acoustic effect than an electro-acoustic effect, although it could be both, following particularly the papers of Adrian and Bawin. Coincident with problems with power systems and earthing systems as causes and propagators of the Hum appear to be reports of the same in association with childhood cancer.
The Hum has been a puzzling psycho-acoustic phenomenon for the last 60 years or so. First heard in Britain in the 1950’s, then extensively in Britain since the 1970’s and then very extensively in recent years. In the USA the Hum’s evolution followed a similar pattern but initially delayed by some 20 years or so. Nowadays the Hum is heard/perceived to some extent in virtually all corners of the globe including, for example, Australasia, Canada, South America and China with the exception of some remote parts of Africa and the former Soviet Union, see http://www.drchrisbarnes.co.uk/lfnhum.htm .
The Hum is thought to be heard by between 2-11% of the World’s population with the peak age for hearing/perception being between 50 and 60 years of age. Yet people significantly younger and older than this age group are also hearers, known in some circles as ‘Hummers’. Those afflicted by the Hum hear/perceive an irregular pulsating noise rather like an irregularly idling engine and usually the noise is stronger indoors and in the night-time hours. There are variations described ranging from musicals tones between 30-80 Hz to sharp pulsations and pressure in the ears. Sometimes the noise seems as if it is behind the ear or head or all-round the victim but just in the air close by. Other times there are body vibrations. Clearly, to some extent these are symptoms of exposure to infrasound and/or LFN ( low frequency noise).  , . Here the work of Moller and Lydolf is also particularly relevant .
However, the original Taos Hum in the USA could not be audio recorded in any way, see Mullins and Kelly (1995) . It could be that the equipment used had insufficient sensitivity or that audio was not the vehicle by which that particular Hum was being perceived. Moreover, there has always been a suspicion by some that the Hum is somehow associated with electrical power systems. This is borne out in both countrywide and world-wide geographic distributions as the Hum as adjudged by both analysis of the IP addresses of visitors to Hum information websites and by direct entries of afflicted persons in a more recently established ‘World Hum Database’. An extract from the original informal Taos Hum report is interesting in this context:
‘’One curious aspect of readings taken in the field north of the Saltzman house was the high levels of 60-hertz signals and their harmonics (signals at 120 hertz, 180 hertz and other multiples). (Hertz is a measure of frequency.) Measurements showed that these signals were present on the Taos area electric power grid. "It was apparent that stray fields along the ground were quite strong, even well away from any power lines," according to the team's report. "However, there were no firm indications that the presence of these strong overtones were somehow responsible for the hum."
Similarly an extract from Cowan 2008  regarding the famous Kokomo Hum investigation reads:
‘Since many affected residents mentioned unusual occurrences related to home electrical systems, including appliances suddenly burning out and cars having remote starters unexpectedly starting in garages, electromagnetic fields were monitored in areas where residents appeared to be most affected. In most cases, elevated electromagnetic field strengths of 3 to 50 milliGauss were experienced in and around the homes.’
‘When asked what changed in their environment at the time they began sensing the
hum, most referred to utility work associated with telephone, cable television, or power line maintenance, or a new cell phone tower in the neighborhood. Since being
involved with the Kokomo Hum study, the author has been contacted by people from
many areas of the United States, as well as Europe, with similar stories to those in
the Kokomo area, both in terms of symptoms and environmental changes. Hums are
clearly not localized to Taos and Kokomo.’ Extracted from Community:
9th International Congress on Noise as a Public Health Problem (ICBEN) 2008, Foxwoods, CT 
Very recently indeed I have added the final two pieces of the jigsaw regards the Hum and power systems. The Hum has become far more prevalent and its effects seem to have got a lot worse since the advent of renewable energy systems which are very prone to both inter area oscillations and harmonic injection due to phase imbalance, see Barnes 2013 . Furthermore even with these systems in place, countries only also experience the Hum if they have TN earthing systems, especially PME and it is more so accentuated by neutral current taking parallel routes in water and gas pipes. PME with such additional current is known not only to propagate harmonic but also to increase the stray electric and magnetic fields within residences, see Barnes 2015 .
In terms of Hum generation by the power grid and subsequent propagation, we are looking at a number of physical processes some of which are easy to explain and others immensely complicated and the resultant acoustical and electromagnetic processes which cannot readily be separated and occur either simultaneously or with quasi-coherence. Additionally, there is the possibility of mixing with other anthropogenic signals or even those from preternatural sources.
A magneto-acoustic mechanism of Hum detection/perception by human beings is the only one which can fully explain all the anecdotally listed properties of the Hum .
This paper aims to answer two questions: firstly is there any independent research to back up such a claimed mechanism and secondly there an electro-acoustic mechanism an equally valid possibility given the distribution of world Hum cases and the link with power systems.
I) Anecdotal reports: there is a significant body of anecdotal evidence on –line although doing science with this is difficult in the extreme as forums on the Hum have attracted the insincere as well as the genuine. Nevertheless, if the full circumstances of the majority of accounts of Hum perception are to be believed, particularly with respect to what happens when hearers enter various types of cave then a magnetic hypothesis better accounts for the phenomenon than does a purely acoustic or gravitational one 
II) Personal Experience and Personally acquired scientific data : I have published extensively on this in the past. Being a Hum hearer myself since 2005 and having several members of my family who also hear/perceive the Hum has allowed scientific measurements to be performed at times when the Hum is present and timers when it is not 
In brief; summary certain combinations of infrasound and acoustic sound are found in my premises when the Hum is present in combination with subtle changes in mains harmonics frequencies as measured in local ground currents, with a toroidal search coil and on ‘wall voltages’. Wall voltages have also been discussed by others in the past see Dawes for example. On some occasions the Hum is seen to intensify severely and be almost un-screenable by the use of ear plugs. It might be possible to regard this as just an increase in the amplitude of the infrasound and acoustic components were it not for the fact that also it is uniquely coincidental that under these conditions, the LF spectrum as detected[C1] by the toroidal coil, becomes more like a comb spectrum even at frequencies below 50 Hz.
Ever since first hearing the Hum, the author and his wife appear to have become sensitised to LFN and LF magnetic signals. Thus not only can we experience Hum like effects by synthesis of infrasonic and acoustic frequencies but also in the case of being in a parked vehicle when the engine is off and when the PWM controller is in the process of dimming the interior/ vanity lights and in a second case of being in the car when parked underneath high voltage power lines, which are NOT emitting corona noise or Aeolian tones, see for example but not exclusively Barnes 2012 . In the case of the former, only a magnetic comb spectrum can be recorded and thus any infrasound or acoustic sound must be well below the threshold of detection of our laptop/microphone/spectrum laboratory software system but in the case of the latter both magnetic and acoustic spectra are recordable. Since the laptop system uses a colour spectrum waterfall type display it is adjustable to pick up sounds virtually at the threshold of human hearing perception. The inevitable conclusion must, therefore, be that in the case of the noise perceived in the car when the light dims, we must be experiencing either ELF magnetic perception or our low frequency hearing threshold must be incredibly enhanced by the presence of the concurrent/ coherent ELF field. In an additional test to make sure this is not due to visual synaesthesia we also closed our eyes and could still hear/perceive the Hum like effects.
III) Independent Scientific Research on electro-acoustic and magneto-acoustic audition especially if any is available which suggests such phenomena are possible within the range of frequencies and field strengths encountered by subjects in Hum locations.
For example, Fisher et al (1975)  stated that there is evidence to suggest that auditory and vestibular systems can be stimulated by forms of energy other than sound, gravity and motion.
Perhaps the earliest and most relevant paper is that of Adrian (1977) . This mentions specific frequency ranges wherein auditory (electrophonic) and visual (phosphene) sensations were generated in human subjects through direct stimulation by low-frequency electric currents. The effects occurred at frequencies in and near the ELF (extremely low frequency) communication band. Frequency-response characteristics for both effects were measured. Both sensory modalities were found to behave much like frequency-selective filters but with a number of important nonlinearities. The minimum thresholds of current for the phosphene and auditory effects occur, respectively, at 18 to 22 Hz and 60 to 90 Hz. The effects were also generated by the application of two simultaneous sine waves well above the cutoff frequency when the difference frequency was near the minimum threshold. Habituation of the phosphene and of the auditory response was noted. These effects and difference-frequency effects may be of crucial importance to the Hum.
Bawin et al (1975)  using animal studies tested the effects of weak electromagnetic fields have been tested on the efflux of calcium from cerebral tissue of chick and cat. The data strongly suggested that the binding and release of calcium occurs cooperatively as the result of long—range interactions between anionic charge sites on the binding substrate. Extremely low frequency (ELF) fields at frequencies of 6 and 12 Hz and gradients in air of 0.1 to 0.5 V/cm decreased calcium efflux by 12 to 15 per cent. Such electric field strengths are not impossible in the home situation.
Counter and Bawg (1992)  showed that in deaf patients, non-invasive extracranial magnetic stimulation (EMS) could evoke auditory sensations. The patients were fitted with standard earplugs and were stimulated at the auricle, the mastoid and the temporal lobe area.
Wood (2008)  analysed all the available literature with regard to the threshold electromagnetic field stimulation of retinal phosphenes and found it to be only 56mV/m , which is well within the range of power frequency fields in typical residences. For peripheral nervous stimulation an average of 2 volt/m was required.
Budak et al (2009) , although working with significantly higher electric field strengths did show that these can alter cochlear function and oto-acoustic emissions in rabbits.
Cook et al (2004 )  showed that resting EEG function is disturbed by ELF fields, particularly in the alpha frequency range (8-13 Hz).
Werthheimer and Leeper (1979)  remarked on an excess of electrical wiring configurations suggestive of high current-flow in Colorado in 1976–1977 near the homes of children who developed cancer, as compared to the homes of control children. The finding was strongest for children who had spent their entire lives at the same address, and it appeared to be dose-related. It did not seem to be an artefact of neighbourhood, street congestion, social class, or family structure. The reason for the correlation was stated to be uncertain but possibly due to effects of current in the water pipes or of AC magnetic fields.
London et al also had w results which support an association between childhood leukaemia risk and wiring configuration, but not direct measurements of electric and magnetic fields, see .Am J Epidemiol1991; 134:923–37 .
Albohm (1988) reviews existing literature, some hundred or so papers in the area of magnetic fields and Childhood cancer and whilst he concludes there is mixed evidence, some positive and some negative conclusions and some flawed experimentation he nevertheless concedes that there is a strong suggestion the area of research should be further pursued. Even doubters such as Preece et al reached similar conclusions .
Wertheimer et al (2005) makes a significant step in identifying non-vertical magnetic fields in association with ground currents in the home. Substantial ground currents are most often found in homes having conductive plumbing, in which an uninterrupted metallic path in the water pipes and water main connects the grounding systems of neighbouring houses. They obtained information on plumbing conductivity was obtained from water suppliers for the homes of 347 cases and 277 controls identified in an earlier study of magnetic field exposure and childhood cancer in the Denver area. An increased cancer risk was observed for children in homes with conductive plumbing: The matched odds ratio was 1.72 (1.03–2.88) and increased to 3.00 (1.33–6.76) when analysis was limited to cases and controls who were residentially stable from the reference date to the study date. A measurement metric likely to indicate active ground currents (measurements having above-median intensity and a nonvertical orientation of <55° from the horizontal) was identified. In contrast to measured field intensity alone, for which only modest associations with cancer have been reported, this metric shows a high and significant cancer risk [matched O.R. = 4.0 (1.6–10.0)] consistent over a range of intensity and angle cut-points. Such elevated non-vertical fields were also associated with cancer in an independent data set, which was gathered to study adult nonlymphocytic leukemia in the Seattle area. The associations of cancer with conductive plumbing and with this exposure metric both suggest that cancer risk is increased among persons with elevated magnetic field exposure from residential ground currents.
Swanson (1996)  has shown that in the majority of homes in the UK, background power-frequency magnetic fields come from currents in final distribution circuits. In these circuits, load currents produce a negligible external magnetic field. The fields in homes arise from net currents, produced when neutral currents divert out of the distribution cable through earth connections. Neutral-to-earth connections occur as part of protective multiple earthing, which is applied to 64% of underground circuits and 32% of domestic consumers' installations, and also occur accidentally within up to 20% (and probably substantially more) of homes. Further they showed the 48 h average net current in a sample of 21 circuits was 3.6 A. Because net currents are produced by diverted neutral current, they vary as loads vary. However, neutral current is proportional not to total load but to the unbalance between the three phases, and this weakens the correlation between net currents and loads. Individual unbalanced loads can lead to disproportionately high net currents. Thus Swanson suggested that the best way of assessing average magnetic fields in residences (which is necessary for epidemiological studies) remains by direct measurement over at least 24 h.
Such currents due to load imbalance on outside circuits can still produce magnetic fields even if the main switch at the consumer unit is switched off. Hence killing the power in a residence does not necessarily kill the experience of Hum for the residents.
Links between the Hum and Cancer will be discussed in the near future more extensively elsewhere.
Kaune et al (2005) made a comprehensive study of residential magnetic and electric fields. They built a magnetic flux density (MFD) and electric-field (E-field) data-acquisition system for characterizing extremely low-frequency fields in residences. Every 2 min during 24-h periods, MFD and E-field measurements were made in 43 homes in King, Pierce, and Snohomish counties of Washington State. The total electrical energy used in each residence during the 24-h measurement period was also recorded, and maps were drawn to scale of the distribution wiring within 43 m (140 ft) of these homes. Finally, on a separate date, field measurements were made in each home during an epidemiological interview. The results of their study were summarized as follows: 1) 24-h-average MFD measured at two separate points in the family room were correlated, as were a 24-h-average bedroom measurement and the mean of the two family-room measurements. 2) The 24-h-average family-room MFD and E-field measurements were uncorrelated. 3) The 24-h-average total harmonic distortions of family-room MFD and E-fields were less than about 24% and 7%, respectively. 4) Residential MFD exhibited a definite 24-h (diurnal) cycle. 5) The 24-h-average and interviewer-measured MFD were correlated. 6) Residential 24-h-average MFD were correlated with the wiring code developed by Wertheimer and Leeper.
It is interesting and significant to note that MFD followed a diurnal cycle, so does the Hum. MFD also had upto 24% THD far greater than E-field ( more than three times). MFD and EFD were uncorrelated. Perhaps this accounts for what the author describes as acoustic Hum and magnetic Hum. Perhaps magnetic Hum occurs when THD is maximised ( i.e. when comb spectra are observed).
Conclusions and Discussion
The present work strongly suggests the notion that PME earthing systems, brain and audition research can yield up secrets of the Hum. All three branches of the evidence considered produce elements of corroboration.
There is far more evidence for the Hum being a purely magneto-acoustic effect than an electro-acoustic effect, although it could be both, following particularly the papers of Adrian  and Bawin  and given that similar values of electric fields can be found in premises.
Coincident with problems with power systems and earthing systems as both causes and propagators of the Hum there would also appear to be reports of the same in association with childhood cancer.
Amateur Hum investigator John Dawes has recently flagged up the cancer connection on his website and thus I will discuss this in another paper, hopefully to be released in the not too distant future.