A loudspeaker from the Underworld, Local Active corrosion protection: a possible feature in Britain’s Low Frequency Noise (LFN) Phenomenon more commonly known as the Hum by Dr Chris Barnes, Manager at Bangor Scientific and Educational Consultants, November 2015. E-mail firstname.lastname@example.org
The enigmatic low frequency noise (LFN) phenomenon known as the Hum was first reported on a widespread basis in Britain in the 1970’s. The Hum is often considered as distinct from other forms of LFN in that its source often seems un-locatable and un-recordable  and hearers sometimes report earplugs as being rather ineffective as a defence. Other than the work done by the present author  and a tiny handful of Universities in the UK there appears to have been little serious effort to properly understand the phenomenon. In fact Hum research has been a field wherein amateur investigators such as Dawes , for example, have possibly made as many and as significant contributions to those of academics.
People who hear or perceive the Hum is often labelled ‘Hummers’ and it would seem that in one mode of perception of the phenomenon they are far more sensitive than average to low frequency noise. This does not rule out that there could be other modes of signal perception in some sensitive individuals either not related to low frequency noise or accompanying it such as magnetic perception and these have been discussed by the present author elsewhere . The Hum is sometimes described as the noise of an idling engine or throbbing sound. These are also described as the effects of infrasound  .
One major problem with doing science on a phenomenon such as the Hum is because relatively few people experience it, one is often left to rely on anecdotal reports. With the advent of the age of the Internet and Global communications, hearers of the Hum, worldwide have formed forums and discussion platforms regarding the phenomenon [6,7]. This has led some to suggest that somehow the Hum is now a single worldwide phenomenon. This is very different to the experience of the Hum in Britain in the 1970’s and the early experiences of the Hum in the USA in Oregon in 1976 with an explosion of cases by the early 1990’s. Where the former was put down to noise from motorways and Gas Mains  and the latter only to a specific set of Industrial sources in Kokomo  with all the other US cases remaining unsolved and with one author, namely, Deming, suggesting that both correlated in time and space to a certain type of military communications aircraft .
The present author has come to the conclusion that most modern Hum cases correlate spatially with renewable energy systems, especially wind power  and certain types of hydro-power. In this latter respect it is interesting to note that Oregon is one of the USA’s most major source of hydro-power and is where their Hum was first experienced. Because the Hum is a subjective phenomenon or possibly group of phenomena, different people describe hearing slightly different noises. It is a well-known fact that once sensitisation to any sort of LFN has taken place, the hearer will generally be more receptive to similar frequencies whatever the source (Oud). If the Hum has predominantly an infrasound compound then clearly it will be un-recordable using traditional microphone based equipment. Oud  has discussed the notion of an un-recordable LFN beating with a higher frequency component and I too have discussed this in terms of cochlear mechanics . Another reason why the Hum may be very pervasive for some is if it has an electric or magnetic or gravitational component. For example a Hum with a magnetic component accounts for why some can hear the Hum in certain types of deep underground cave . It also accounts for why in some cases earplugs are ineffective.
The present author has also discussed the notion of local and distant Hums. Some distant Hums may involve the ionosphere and atmosphere as a generating/propagating medium and/or similarly the solid earth. There is a very strong case for the involvement of power systems in some cases of the Hum even predating wind energy. Local cases of the Hum may be caused by acoustic and infrasonic signals from the same or from multiple sources provided that certain frequency relationships are satisfied. With regard to electrical power systems it seems that when they are behaving badly, due for example, to phase imbalance creating multiple harmonics and subharmonics and more likely with wind power, the Hum phenomenon also seems worse. Yet at least in Bangor Wales and in some of the surrounding area it seems that some of the frequencies capable of causing the Hum are detectable over ducts carrying each of the three utilities. See all my papers at reference  for a full explanation of what is contained in this very condensed paragraph.
The Hum in Britain began to be reported extensively in the 1970’s when there were major changes in infrastructure. The first pumped storage power stations had been built, gas was no longer stored in large holders but was piped at high pressure and controlled by compressors and spring loaded regulator stations. Active corrosion protection began to be used on power systems, sub-stations, gas distribution and at gas pressure reducing stations.
The Hum gas or electric or both and active corrosion protection (CP) a loudspeaker from the underworld, a new hypothesis
In the 1970’s active corrosion protection began to be used extensively on pipelines, at power substations and at all gas pressure reducing stations. Although the DC voltage which needs to be introduced and maintained between the pipe or structure and the set of protective electrodes is small and the current density likewise because the volumes/areas covered can be large the rectified current capability of the protection unit itself can be large. Thus one can conceive the presence of a non-uniform DC or quasi-DC (half-wave rectified) magnetic field in the local region of the unit and immediate underground. Some CP systems are also pulsed. Some explanations of CP systems are to be found at references  and .
Even in the absence of pulses there is also present the earth’s ever present field and additional electromagnetic fields from electricity infrastructure. There is also the possibility of pipeline pulsations causing pressure wave modulation of the ion flow and causing additional induced fields. Thus we may hypothesise we have an underground system not unlike, but rather more complicated than Magnetoacoustic tomography with magnetic induction (MAT-MI) which is an emerging approach for noninvasively imaging electrical impedance properties of biological tissues, see for example Hu (2011) . MAT-MI imaging systems measure ultrasound waves generated by the Lorentz force, having been induced by magnetic stimulation, which is related to the electrical conductivity distribution in tissue samples. Given the frequencies involved, I would expect our ‘in street’ or ‘under tarmac’ version of MAT-MI to generate acoustic and infrasonic frequencies with sum and difference frequencies associated with powerline frequencies, their sub harmonics as well as inter alia their inter and intra area oscillation and flicker frequencies and the pulsation frequencies of the gas pipes involved. Further, I would expect some phase coherence between some of the acoustic frequencies and magnetic field frequencies involved. Given that human beings have evolved on a planet where they are exposed to feeble ELF fields ( so called Schumaan resonance) and have strikingly accordant brain rhythms with the former, see for example Cherry (2002) , I would expect such acoustic and magnetic signals from the tarmac underworld to be potentially disturbing or even very disturbing to some humans, viz a viz The Hum.
An additional facet is that DC currents associated with CP will cause ionic charge separation and the possibility of numerous two way electroacoustic effects such as, for instance, electro seismic conversion or electrolytic style loudspeaker action. Electroacoustic phenomena arise when sound waves propagate through a fluid containing ions. The associated particle motion generates electric signals because ions have electric charge. This coupling between ultrasound and electric field is called electroacoustic phenomena. Fluid might be a simple Newtonian liquid, or complex heterogeneous dispersion, emulsion or even a porous body. There are several different electroacoustic effects depending on the nature of the fluid.
Ion Vibration Current/Potential (IVI), an electric signal that arises when an acoustic wave propagates through a homogeneous fluid.
Streaming Vibration Current/Potential (SVI), an electric signal that arises when an acoustic wave propagates through a porous body in which the pores are filled with fluid.
Colloid Vibration Current /Potential (CVI), an electric signal that arises when ultrasound propagates through a heterogeneous fluid, such as a dispersion or emulsion.
Electric Sonic Amplitude (ESA), the inverse of CVI effect, in which an acoustic field arises when an electric field propagates through a heterogeneous fluids.
I hypothesise that this might be a potential amplifier of ground emitted pipe and other vibrations or an electro –seismic converter creating ESA for pre-existing a.c. ground currents. I set up an experimental electrolytic cell to test this notion.
Experimenting with electrolytes and active CP style signals
I set up the apparatus as above. A ‘Feedback’ Sine Square Oscillator type SSO603 was used to drive an AC691-N speaker system and the remote output jack was connected directly across the Aluminium foil electrodes immersed in saturated sodium chloride solution. The lower electrode was formed in the shape of a cup to focus sound waves upwards. A piece of 60/40 solder was used a sacrificial electrode. This was brought into very close proximity with the cup electrode. The system could be driven into oscillation from about 100Hz – 8 KHz and displayed a broad resonance at about 2+/.5 KHz. Even so the emitted sound level was extremely low and barely perceptible to the human ear. However, it could be significantly enhanced by about 20dB by pulsing on 12 volt DC at approximately 1 second intervals as shown. Any attempt to leave the DC flow on continuously was counterproductive to acoustic amplification as the bubble cavitation noise due to electrolytic action was overwhelming.
This simple experiment illustrates that at least under laboratory conditions a pulsed DC current, similar to that used in some CP systems can enhance AC acoustic emissions. It is thought that something similar occurs on a grand scale with CP protected buried infrastructure and the moist earth acting rather as a loudspeaker from the under- tarmac world. I have previously mentioned how the Hum in Bangor appears as a very easily damped Rayleigh wave at my premises and how passing vehicles appear to very readily disturb it.
Neither my wife nor I had ever heard the Hum before coming to reside in our present address, which incidentally is located only some 35 metres or so from a spring controlled gas pressure reducing station with local active cathodic protection. Even our son hears the Hum sometimes and he is well below the peak age for Hum perception. Some people report hearing the Hum in the vicinity of high voltage power lines, I am not talking of corona noise here. As a scientist and engineer, I know the difference. High voltage lines in the UK now almost always share their route corridor with the high pressure buried gas pipeline grid and are known to induce significant voltages into them which can disrupt cathodic protection just as much as GIC’s from solar storms. Presumably all have the potential to give enhanced ground borne sound and emf production.
This practical experience seems to strongly support the above hypothesis. Either when AC fields meet CP systems or when a Gas Pipe is subject to mechanical vibration as with gas pressure fluctuations in the presence of induced CP the Hum seems to be locally manifest. Yet nothing in this statement detracts from other causes of the Hum as an LFN or even part preternatural phenomenon whether locally generated or propagated from afar.
Do the frequencies observed make sense?
The propagation speed of sound in soil varies between 50-300m/s. Assuming infrastructure buried at approximately 1m depth, pseudo resonances in the tens or hundreds of Hz region are to be expected.
AC source frequencies available will be 50 Hz and its sub and higher harmonics. These will also be subject to modulation by flicker (typically wind turbine blade crossing frequencies and the like). Natural and anthropogenic seismic signal frequencies will also be available. Pulsation frequencies of the gas grid will also be available. Thus frequencies are available which could match and sustain any likely resonances.
Many electricity installations as well as gas installations use active CP. CP signals are sometimes pulsed for corrosion investigations and infrastructure location  (Koleva (2006). This will also complicate the issue. Since much modern utility infrastructure runs close together, electromagnetic and acoustic crosstalk might be to be expected. It is instructive therefore to explore a spectrum analysis of signals on the various networks.
I previously made an acoustic study of Bangor and LlanfairPG made in the frequency range 0-313 Hz approximately  and considered the different utilities as sources of sound for the phenomenon known as the Hum. Essentially, the hypothesis of Vasudevan and Gordon (1977), Institute of Sound and Vibration Research University of Southampton ) was confirmed with regard to the presence of the Hum in the context of a highly skewed acoustic spectrum but not necessarily within the context of signal origin. I showed that the Hum generally requires a substantial infra sound component, some sort of narrow band acoustic signal(s) of constant frequency within the range 30 -80 Hz and minimal or zero acoustic sound above that frequency range, this is also exactly consistent with Oud’s paper . Signals from both the power grid and gas mains can produce Hum most of the time in parts of the village of LlanfairPG whereas at the author's house the Hum comes and goes according to propagation of infra sound and seismic sound from larger distances away particularly when there is instability in a particular 400KV circuit in the electricity grid giving rise to sub-harmonic and inter-harmonic acoustic noise.
I also reached the conclusion that Hums in the Bangor and Anglesey area are very likely caused by either the electricity grid behaving badly and/or the High Pressure gas grid. There was an unknown signal of 14 Hz on the water mains only found in Bangor within this study. The gas grid was found capable of generating very similar frequencies to those obtained with mains sub harmonics but also generates frequencies around 56 and 73 Hz not seen underneath power grid circuits. It is very interesting to note that Tom Moir recorded a frequency of 56 Hz as being associated with the North Shore New Zealand Hum. It is believed NZ has similar methods of Natural Gas distribution to the UK. A frequency of 44 Hz was also observed. This is suggestive of 50HZ+ /-6 Hz as being potentially present on the gas mains in Bangor. The much lower frequency periodicity of the Hum could not be readily recorded and possibly arises as a result of wind turbine infrasound and/or wind turbine flicker on the 50 Hz signal.
It is interesting to note that some kinds of high power pipeline fault finding equipment which can be connected to CP points produce frequencies of 3,4,6,8.64,98 and 112Hz, see http://www.vivax-metrotech.com/UploadFiles/image/vLocDM_Brochure_VXMT_Eng_V2.0_20100531%20%28vxmt%29.pdf .
Firming up the link with gas
Spring loaded gas pressure reducers are most likely to introduce pressure fluctuations at minimal and maximum flow rate  and similarly auditory Hum, see Zafer and Lueker, Applied Mathematical Modelling (2008) . The author has often noticed the Hum to appear to peak at about 11pm and 6 am. These are presumed times when gas flow rate will be changing dramatically as heating systems switch off and re-start? Recently major gas mains renewal has taken place in parts of Bangor and with it the Hum intensity seems to have reduced dramatically. Unfortunately, one can only make qualitative statements at present and a note of caution should be raised as quite often pumped storage power begins pumping and ceases pumping at about the same times as the above .
More than just infrasonic/acoustic
Previous evidence has been presented to suggest that human perception of the Hum can involve multiple mechanisms. In the author’s previous publications he has referred to one instance of which the Hum in Bangor seemed to manifest magnetically. More recently other similar instances have been noted. It seems that there is a ‘magnetic’ polarity associated with the Hum and that sleeping in a certain direction can either enhance or reduce its intensity. This is not thought to relate to acoustic directivity since 27dB attenuating wax ear plugs were in use at the time.
A possibly hypothesis here is that CP induced magnetic field may be either counter to or reinforced with the earth’s natural field and Schuman resonance signals. Associations between the Hum and the IMF have been reported previously . It is hoped to report more extensively on this phenomenon at a later date.
Discussion and Further work
Examples of severe corrosion have been noted with incorrectly installed gas meters.
Here metallic structures have the potential to short out the ‘CP’.
It is instructive to note that gas meter inputs and the house gas piping connection are in effect electrically isolated from each other and have to be so because of the use of active CP [http://phmsa.dot.gov/pv_obj_cache/pv_obj_id_FE0D2DB95F943A92A45D7C084C4B07CAABC01200/filename/smalllpgas-chapt8.pdf . An experiment could be conducted at premises which experience the Hum to effectively ground the CP signal and note any changes in the Hum. Any observed changes whatsoever would be in strong support of the present hypothesis.
It is quite feasible as a facet of evolution or environmental exposure that Humans may be becoming more magnetically sensitive. This could either be due to constant or intermittent exposure to RF which can re-organise metal ions and metallic nanoparticles within the body . Alternatively and/or additionally, the supply of environmental metallic Nano-particles in our environment is increasing due to industry, road use and aviation use .
This magnetic sensitivity may be responsible for the link between two apparently at first sight very different but potentially related manifestations of Hum like phenomena. Because the Hum is highly subjective and because once Infrasound/(magnetic) ELF sensitivity has developed it is hard to shake it becomes possible for Hum like effects to become perceived in unlikely scenarios. Thus some subjects can perceive the traditional Hum as strongly suggested to be associated with gas and electricity infrastructure whereas others can additionally perceive a Hum in motor vehicles parked at critically very specific distances from certain digital transmitting antennas and thought to be associated with the imparting of modulation information directly by magnetic vector potential.
Active corrosion protection and associated pipeline test protocols are potentially a new and hitherto undisclosed possible feature in Britain’s Low Frequency Noise (LFN) Phenomenon more commonly known as the Hum and such systems and protocols may have the potential to amplify and increases noises from buried infrastructure giving us an unusual and uncontemplated loudspeaker from the tarmac underworld! An experimental laboratory system albeit based simply on electrolyte solution produced some 20dB of acoustic gain more than sufficient to make a inaudible Hum audible, although the frequencies were not those of the Hum appropriate scaling to the roadside situation is suggestive that such frequencies known to be present could be amplified. Moreover CP may induce weak time varying magnetic fields comparable with the earth’s natural field to which we humans are presumably sub consciously attuned, particularly with respect to Schumann resonance. A combination of infrasonic and low frequency acoustic field together with a coherent magnetic field appears to be the set of conditions required to generate the most pervasive Hum. Such a set of conditions may have inadvertently been introduced in the UK from the early 1970’s onwards as a result of utility infrastructure changes.
It would be very instructive to interview a large number of a Hum hearers and establish if they live near installations wherein active CP is used. Although the Hum has become far more prevalent in recent years and seems to correlate with renewable energy I can’t help but wonder if our tarmac underworld were not now full of DC and pulsed DC currents in addition to phase imbalanced AC currents perhaps we may never have had the Hum?
I am grateful to the unnamed employees of Wales and the West Utilities whom I interviewed regarding system pulsations. I am grateful to an unknown CP survey team I recently interviewed. I am grateful to my wife Gwyneth for valuable support and discussions during the preparation of this work.
2. Mullins and Kelly 1995 http://acousticalsociety.org/sites/default/files/docs/echoes/v5n3.pdf
5. (Poulsen and Mortensen Working Report 1 to Danish Environmental Protection Agency 2002).