Smart Grids a potential new vehicle for rural and urban LFN nuisance (or the Hum) and its acoustic component, is there a simple way Smart Grids could be inadvertently maximising this human inconvenience? By Dr Chris Barnes, Bangor Scientific and Educational Consultants, e-mail firstname.lastname@example.org
The Hum is defined and its history is discussed. A brand new and simple hypothesis is advanced for the increasing prevalence of LFN/ the Hum in terms of the operational behaviour of pre-existing domestic, commercial and industrial noise and vibration sources at night changing from the previously random to the precisely controlled under the influence of Smart Power Grids.
The Hum is a geo-sporadic noise nuisance heard/perceived by an estimated 2% of the world’s population, this figure probably rises to well over 10% in the 40-70 age groups. The noise, an irregular pulsation like very low pitched buzz, can be extremely irritating and annoying and in its extreme even cause stress related illness and sleep deprivation. It is mainly but not exclusively in buildings at night even with the power switched off and is characterised by the sound of a slowly and irregularly (quasi –periodically) idling engine and these days is perceived by the present author as often more sharply pulsing than musical. Those musically minded hearers of the first instance of the Hum in the USA, the so called Taos Hum toned matched it between 30-80Hz and stated that it has quasi-period modulations or fluctuations of between 0.5 and 5Hz. Others describe a higher pitched buzzing yet still with the same sort of underlying modulation. Another strange facet of the Hum is that is either difficult or impossible to audio record, this has been particularly so in the past before the advent of readily available FFT systems. Sadly this has pushed the Hum, for some, into the realms of Science Fantasy. This paper, as with the other works of the present author, aims to demystify the phenomenon.
Everything but power systems has officially been blamed for the Hum. Scientists at Southampton University concluded it is simply distant noise. Wikipedia blames amongst other things colliding waves under the ocean. Applying critical thinking one immediately wonders why then distance noise or ocean waves shouldn’t cause the Hum in the bulk of Russia and Africa and other places which either don’t or until recently haven’t experienced the Hum.
Contrasting all kinds of infrastructure between places that don’t and do experience the Hum and using world mapping it has recently been shown that the Hum is best correlated with sites wherein there is connection of renewable energy to the power grid. Another common denominator with power grids which use a considerable proportion of renewable energy is that they tend to be so called Smart Grids. Smart Grids tend to control their power flows, amplitude and frequency by means of communication networks running as part of the Grid itself or in parallel such as radio links or optical fibre links. Long time amateur Hum investigator John Dawes has suggested power systems may be to blame since the first Bristol and Largs Hums in the UK in the late 1970’s and early 1980’s but has never been able to be specific about which elements of such systems were the cause, instead John has referred to the general upgrading of the grid which took place in that era. John does however have quite a controversial theory of how the Hum might be perceived in terms of gravity modulation. The present author can see at least three physical mechanisms as to how this can occur but not everyone might understand or agree. All of these mechanisms will also modulate air pressure to a greater or lesser extent and some have made observations on the Hum in respect of barometric changes. It is imagined that John came up with his hypothesis to account for lack of audio recordings and to explain how some deaf people claim to hear the Hum (and presumably describe the same noise as hearing people) and as to accounting for how the Hum is sometimes difficult to screen with ear plugs.
The present author has previously explained the more complex facets of the Hum an in particular how some people can perceive the Hum in unlikely places and how deaf people might be able to perceive the Hum. These types of perception require a magneto-acoustic hypothesis of both Hum generation and perception  or the former hypothesis of perception and an alternative method of perception involving gravitation [2, 3].
However the question now posed is can Smart Grids, in conjunction with renewable energy account for the recent World-wide explosion in cases of LFN/the Hum? Not discounting previous valid hypotheses of the Hum, particularly as in its relation to ground currents and dirty electricity (Havas and Stetzer 2004) which has recently been independently asserted by some Canadian researchers , can there be a simpler purely acoustic cause of the Hum arising from every day domestic and commercial sources controlled by smart grids? It is certainly known that such sources can contribute to Hums, take Kokomo for example, see Cowan (2008) . Yet to date domestic, commercial and industrial sources of the Hum have been the exception rather the rule. Until very recently indeed, there have been no significant cases of the Hum in Russia or China. The author feels this is likely to change more as both countries invest in Smart Grid Technology and possible change from TT to PME electrical earthing systems.
How Smart Grids can change the operation of mundane every day noise and vibration sources for the Hum.
Taking the behaviour of the UK Power Grid as an example is particularly instructive. The present author has already pointed out how smart grids and renewable energy contribute to power flow oscillations and harmonics and how these can impact on both noise from generation in the rocks and soil directly under buildings experiencing the Hum . It is also described in the literature how banks of capacitors particularly associated with industrial electricity supply can vibrate and be a source of LFN.
But what of more mundane and pre-existing potential noise and vibration sources such as domestic, commercial and industrial refrigerators, fans, heating systems and compressors? Noise from these types of sources can enter premises by both airborne and ground borne pathways and conduct through walls of attached houses. Prior to the advent of smart grids the operation of such noises would have been almost completely random.
Nowadays in the UK and the USA http://best.berkeley.edu/~aagogino/Slides/JMathieu_BestTalk_4.4.12.pdf 
this is no longer the case. Huge blocks of such devices across swathes of the country will turn on and off as required for frequency control (load bolstering or shedding) and reactive compensation all controlled by the smart grid either by frequency or wave shape sensitive internal circuitry or by radio tele-switching . Tests on Smart Freezers have been going on since 2009 . http://www.greenwisebusiness.co.uk/news/europes-largest-smart-grid-trial-to-be-tested-on-fridge-freezers-843.aspx Such devices will radiate acoustic and seismic signals (if floor or wall mounted) at mains synchronous fundamental frequencies, harmonic and sub –harmonic frequencies and at their own mechanical resonant frequencies, in other words a formula for the Hum. These noises will also fluctuate in amplitude and frequency according to national and local power flow oscillations to boot. In other words we have new and substantial families of coherent night noise sources throughout the country or a particular neighbourhood which previously only behaved randomly. Variations in their propagation paths will be sufficient to introduce the quasi-periodicity of the Hum. Quasi-periodic air pressure oscillations which are a natural phenomenon, , see Delyukov and Didyk (1999)  , could also potentially influence Hum propagation but are not in themselves the source, thus this new and simple theory for the acoustic component of the Hum and its ever increasing prevalence also fits well with the author’ previous observations of the Hum as a phenomenon with both an anthropogenic and a natural component .
According to the present hypothesis, noises generated by Smart Grid controlled devices can propagate several kilometres at night. However, unless the power to entire areas could be switched of it might be difficult to prove this very plausible hypothesis of the Hum. The Hum in the Bangor area is not such a problem in the day time because in the UK, Dinorwig pumped storage hydropower station is used for frequency control instead. The Hum is not always heard in big cities where there is continuous vehicular movement as this destroys any coherence in its ground borne components.
It is not proposed that this present hypothesis explains all cases of the Hum, but could well help account for its recent prevalence in the 21st Century context in the UK and USA in particular.
In addition to ground induced vibration through currents of ‘dirty electricity’ and vibration of capacitor banks at sub-stations, Smart Grids have here been shown to be a potential new source of wide area LFN having the tonal and quasi-periodic properties of the Hum through the acoustic and seismic emissions of commercial and household devices they now regularly and mainly nocturnally control to achieve frequency and load management. In the UK such devices are more likely to be used for such control at night-time as Dinorwig pumped storage plant is exclusively used for this purpose by day. Not all cases of the Hum will be due to this source of LFN but the hypothesis ought to provide a reconciling factor for those who can either accept or comprehend no other means of causality. Certainly the increasing prevalence of LFN/ the Hum can now also be accounted for in terms of the operational behaviour of pre-existing domestic, commercial and industrial noise and vibration sources at night changing from the previously random to the precisely controlled under the influence of Smart Power Grids. This hypothesis does not detract from any of the other work of the present author and can work in parallel with the magneto-acoustic or gravito-acoustic generation and detection of the Hum, see Barnes .
I have commented in the past on the Hum and Earthquake connection, see Barnes 2012 . In the field of earthquake science new types of sensor have recently been developed which exploits changes in the propagation of background ‘underground hum in the frequency range 16-2000 Hz. There is independent confirmation of the type effects I have observed by human sensitivity alone to be at http://earthsciences.typepad.com/files/acous1_05en-1.pdf Belyakov 2005 .
The author wishes to acknowledge his wife and son for valuable discussions of the Hum and further to acknowledge emailed anecdotal evidence sent directly to him from various UK sufferers of the Hum.