Anomalous case of hearing low frequency noise (The Hum) in a motor vehicle some short comments


Dr C. Barnes, Bangor Scientific Consultants.



An anomalous case of the Hum in a certain type of motor vehicle is investigated.

A relationship is found between the turning off of the engine, the appearance of the Hum and a low frequency magnetic comb spectrum in the vehicle.   The personal residence of the author is a ‘Hum hotspot’ but the Hum therein is believed to be infrasonic/ acoustic in origin. However on just one occasion a magnetic comb spectra similar to that in the car was observed at circa 4am in the author’s bedroom. Coincidentally the Hum was at horrendous levels then and virtually un-screenable by wax earplugs or by silver foil.   






Complaints due to disturbance from low frequency noise seem to be increasing throughout the developed world.  A special class of low frequency noise not yet fully understood has been described as ‘The Hum’ (refs).  The Hum is painfully annoying to those afflicted who have variously described it as sounding like either a distant idling diesel truck, a bee trapped in a bottle, very low pitched Morse code   or a combination of the three. Another feature of the Hum is that some people describe it as sounding as though it were coming from behind one ear. 


Anecdotal reports suggest that the Hum is mainly perceived in buildings and predominantly at night. The present author and his wife both perceive the        Hum in their present residence.     There have also been some reports of people hearing the Hum in stationary motor vehicles.  The author and his wife have heard the Hum in their Vauxhall Vectra model             C motor vehicle on several occasions after driving and parking in various locations and indeed this phenomenon was investigated as part of a study on geographic distribution of the Hum and the influence of electromagnetic fields of various frequencies on the Hum.  However, at the time of that study it was not noticed that the amplitude of the Hum as perceived in the parked vehicle declined with time and suddenly ceased. 


It is known by the author as a result of personal experimentation that Hum and Hum like effects can be generated and perceived under a number of different conditions such as those including




Thus it was decided to set up an experiment to see which, if any, of the above combinations was responsible for the decaying Hum in the car.



Experiments and results 


In addition to various locations referred to elsewhere (refs) The Hum could always be heard after parking the car on the drive after any journey even in the daytime.


A significant radio frequency field of several tens of milli-volts per metre was present with components at Tetra, GSM, FM radio and TV broadcast frequencies. The inside of the car was acoustically quiet less than 40 dB A rating.    However, use of a magnetic search coil revealed a significant low frequency comb spectrum of several hundred milligaus spanning the frequency range 4-200   Hz.  The spectrum disappeared when the car engine was started and disappeared some two minutes after parking or switching off the engine.




Conclusions and Discussion.


At least in a Vauxhall vectra C type of motor vehicle Hum perception appears to be anomalous in that it is associated with some facet of the vehicle itself.


The most likely cause of the magnetic comb spectrum is some facet of the car electrical system itself especially as it was always present for a constant timing.


Both individuals present perceived the Hum to cease when the amplitude of the comb spectrum decayed.


The most likely cause of the Hum perceived was a combination of radio frequency and low frequency magnetic fields.


Such combinations have also been known to evoke other types bio-kinetic effects in certain individuals. 


The author and his wife also perceive the Hum inside their residence wherein infrasonic and acoustic fields have been measured at certain times coinciding with the Hum. It is believed that generally these conditions give rise to the Hum indoors. Although there are various other mechanisms discussed elsewhere and yet to be proposed as to how there could also be high frequency electromagnetic field involvement in either    Hum perception per se or at the very least in the enhancement of the amplitude of the phenomenon. (REFS).


However, on just one occasion in the last five years the Hum was truly unbearable and it was impossible to screen it out as usual using wax earplugs and/or silver foil.

On that occasion, a magnetic comb spectra extending from 2Hz –40 Hz was also recorded, quite similar to the intermittent one seen in the car.      It is believed that such spectra may be associated with so called ‘seismic q spikes’ (ref).    


This personal observation of the author is in strong support for the hypothesis presented.


Only by taking into account as much anecdotal evidence as possible and following this up with real site visits and measurements will new Hum theories become fully validated and accepted.  It is hoped to report further in future. The author has recently established interesting personal contacts with another UK Hum Researcher and researchers in Canada and the U.S.