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The Hum is a phenomenon, or collection of phenomena, involving widespread reports of a persistent and invasive low-frequency humming, rumbling, or droning noise not audible to all people. Hums have been widely reported by national media in the UK and the United States. The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the "Bristol Hum" or the "Taos Hum".

Data from a Taos Hum study suggests that a minimum of two percent of the population could detect the Taos Hum, and the Daily Telegraph in 1996 likewise reported a figure of two percent of people hearing the Bristol Hum. For those who can hear the Hum it can be a very disturbing phenomenon. However, amongst those who cannot hear the Hum and some specialists, there has been scepticism about whether it, in fact, exists.

Description

The essential element that defines the Hum is what is perceived as a persistent low-frequency sound, often described as being comparable to that of a distant diesel engine idling, or to some similar low-pitched sound for which obvious sources (e.g., household appliances, traffic noise, etc.) have been ruled out.​ There are a number of audio reproductions of the Hum available on the web, including at least one actual recording.​

Other elements seem to be significantly associated with the Hum, being reported by an important proportion of hearers, but not by all of them. Some people hear the Hum only, or much more, inside buildings as compared with outdoors. Some perceive vibrations that can be felt through the body. Earplugs are reported as not decreasing it.​ For those who can hear the Hum, it can be a very disturbing phenomenon and it has been linked to at least three suicides in the UK.​

The Daily Telegraph reported that two percent of people could hear the Bristol Hum; similarly, research into the Taos Hum indicated that two percent could hear it. The Hum does appear to be geographically focused, i.e. it does appear to be possible for hearers to move away from it; the range of the Taos Hum was reported to be 48 to 72km. Women may be more likely to be affected than men. Age does appear to be a factor, with older people being more likely to hear it.​

The Hum has traditionally been difficult to record; Deming stated in 2004 that there had been no reports of any successful measurements of vibrations or sound associated with the Hum that could not be attributed to ordinary industrial or environmental noise.​ In 2006, however, Dr. Tom Moir of the Massey University in Auckland, New Zealand made a recording of the Auckland Hum .​​ The captured Hum's power spectral density peaks at a frequency of 56 hertz.​ The Taos Hum was between 40 to 80 hertz. Higher-pitched tones have also been reported; the Hueytown (Alabama) Hum has been compared the sound to that made by a dentist’s drill or the sound made by a fluorescent light bulb near the end of its life.​

However, amongst those who cannot hear the hum and some specialists, there has been scepticism about whether it, in fact, exists. In 2009, the head of audiology at Addenbrooke's Hospital in Cambridge, David Baguley, said he believed people's problems with hum were based on the physical world about one-third of the time, and stemmed from people focusing too keenly on innocuous background sounds the other two-thirds of the time. His current research focuses on using psychology and relaxation techniques to minimise the distress, which leads to a quieting or even removal of the noise.​ Leventhall, who prepared a report for the UK government on the subject, similarly suggested that cognitive behavioural therapy was effective: "It's a question of whether you tense up to the noise or are relaxed about it. The CBT was shown to work, by helping people to take a different attitude to it."​

History

Only a handful of articles have been published in the peer reviewed literature, including: Frosch, 2013;​ Deming, 2004;​ Mullins & Kelly, 1998, 1995;​ Broner, 1978;​ Vasudevan & Gordon, 1977;​ others by consultants like Cowan, 2003;​ Leventhall, 2003;​ others in the non-peer-reviewed weekly magazine New Scientist with anecdotal value like Hanlon, 1973;​ Fox, 1989;​ Wilson, 1979.​ Further, there has been little mainstream attention.

The World Hum Database and Mapping Project was launched in December 2012, in order to build detailed mappings of hum locations and to provide a database of Hum-related data for professional and independent researchers.​

Reported hums from around the world, by date first reported:

London and Southampton, UK (1940s)

More than 2,000 people reported hearing sounds dating back to the 1940s in the London and Southampton areas of Great Britain.​

Auckland, New Zealand (1977)

The Auckland Hum was first reported in 1977.​ It is focused on the North Shore, although it has also been reported in the east of the city. Dr. Tom Moir of the Massey University started investigating in 2006. He has reached no definitive conclusions, but the data led him to suggest that it was not related to the electricity mains, common communication devices (e.g. mobile phones, wi-fi, police radio) or military projects. He found that it behaved like a natural phenomena and that it became stronger at lower air pressures. Describing the noise as sounding like blowing over a bottle, he noted that most of the houses were located in dips in the ground.​

He made a recording of the hum.​

Bristol, England, UK (1979)

In Britain, the most famous example was the Bristol Hum that made headlines in the late 1970s.​ 800 people reported hearing it and it was eventually blamed on traffic and factories in Avonmouth.​

Taos, New Mexico, US (1992)

It was in 1992 that the Hum phenomenon began to be reported in North America following complaints from many citizens living near the town of Taos, New Mexico.​

The University of New Mexico undertook studies of hum sufferers in Taos. In one of their tests, hearers were asked to match their Hum with a sound generator, resulting in frequencies ranging from 32 Hz to 80 Hz with modulation frequencies from 0.5 to 2 Hz. The researchers could find no acoustic, seismic or electromagnetic sources that might account for the hum.​

The Taos Hum was featured on the TV show Unsolved Mysteries,​ and it was also briefly mentioned in an episode of The X-Files.​

Kokomo, Indiana, US (1999)

Kokomo, a city of 47,000, allocated $100,000 in 2002 to investigate a hum after nearly 100 complaints were made since 1999. Some sufferers blamed physical symptoms on the hum, including headaches, nausea, diarrhea, fatigue, and joint pain, with one reporting that her health improved when she moved out of the town.​​ In November 2002, acoustic consultants Acentech was hired by the Board of Public Works and Safety of the City of Kokomo to investigate the Hum.

The Acentech investigation found no evidence of ground-borne vibrations within the extremes of human perception. Its investigation of acoustic sources located two sounds that were 20 decibels above background, with frequencies of 36 and 10 hertz. The first was a cooling tower at the local DaimlerChrysler casting plant emitting a 36 hertz tone, the second was an air compressor intake at the Haynes International plant emitting a 10 hertz tone.​ However, even after these noises were addressed to the satisfaction of the consultant, residents still reported hearing the hum.​​

Calgary, Alberta, Canada (2008)

Investigation of the Ranchlands hum began in 2008. Marcia Epstein, an acoustic ecologist at the University of Calgary who is investigating in her spare time, said that whilst there were a variety of tones, there was a concentration of frequencies around 40 hertz,​ sometimes described as a "vibrational feeling",​ affecting "12 to 20 per cent of the community."​ The investigation was ongoing in 2013.​

Windsor, Ontario, Canada (2009)

This phenomenon, first noticed in 2009, has also been reported since 2011 throughout Windsor and Essex County in Ontario, Canada.​ A 2011 study by Earthquakes Canada indicated that it may be originating from the heavily industrialised Zug Island area on the US side of the Detroit river.​ A two-hour telephone town hall meeting in 2012 received calls from 13,000 residents, with another 9,000 leaving comments over the next week, although not all of those were from people who could hear the hum.​

In 2013 the Canadian Government allocated $60,000 for research by the University of Windsor to determine the source of the noise.​ A report released in 2014 confirmed the origin as being from Zug Island, though the precise cause of the noise has not been determined. A U.S. Steel blast furnace on the island was hypothesised to be the source.​ Meetings with U.S. officials and U.S. Steel to discuss the study have begun.​

Woodland, England, UK (2011)

In June 2011, residents of the small rural village of Woodland, England reported experiencing a hum that had already lasted for over two months.​ It has been suggested that disused mine shafts in the area are the main culprit.​

Beaufort, County Kerry, Ireland (2012)

The Hum has also frustrated residents in Beaufort, Ireland.​ This led to it being raised in the Irish Parliament by Michael Healy-Rae, who personally heard the Hum.​

Seattle, Washington, US (2012)

The "West Seattle Hum" in Seattle, US was first reported in the media in 2012, although residents stated that they had heard it in previous years.​ One suggested culprit was the mating call of the Midshipman fish,​ although the University of Washington researcher involved determined that this was not the case in Seattle.​ Local businesses from the West Marginal Way area worked with the West Seattle Blog to isolate and eliminate the noise, which was determined to be coming from equipment used to offload cargo from ships.​​

Wellington, New Zealand (2012)

On 8 October 2012 the city council of Wellington, New Zealand started to receive complaints about a mysterious hum.​ A council investigation failed to locate the source of the noise, with the investigators failing to even hear the hum. It disappeared shortly after it was first reported. The council advanced the theory that the source was a Singaporean naval vessel that had arrived in Wellington the day before the first complaint was received.​​

Possible explanations

Mechanical devices

Although an obvious candidate, given the common description of the hum as sounding like a diesel engine, the majority of hums have not been traced to a specific mechanical source.

In the case of Kokomo, a city with heavy industry, the origin of the hum was thought to have been traced to two sources. The first was a 36 hertz tone from a cooling tower at the local DaimlerChrysler casting plant and the second was a 10 hertz tone from an air compressor intake at the Haynes International plant.​ After those devices were corrected, however, reports of the hum persisted.​​

However, two hums have been linked to mechanical sources. The West Seattle Hum was traced to a vacuum pump used by CalPortland to offload cargo from ships. After CalPortland replaced the silencers on the machine, reports of the hum ceased.​ Likewise, the Wellington Hum is thought to have been due to the diesel generator on a visiting ship.​​ A third hum in Windsor is likely to have originated from a steelworks on the industrial zone of Zug Island.​

Tinnitus

A suggested diagnosis of tinnitus, a disturbance of the auditory system, is used by some physicians in response to complaints about The Hum. Tinnitus is generated internally by the auditory and nervous systems, with no external stimulus. However, the theory that the Hum is actually tinnitus fails to explain why the Hum can be heard only at certain geographical locations, to the degree those reports are accurate. There may exist individual differences as to the threshold of perception of acoustic or non-acoustic stimuli, or other normal individual variations that could contribute to the perception of the Hum by some people in the population and not by others.

While the Hum is hypothesized by some to be a form of low frequency tinnitus​ such as the venous hum, some sufferers claim it is not internal, being worse inside their homes than outside. However, others insist that it is equally bad indoors and outdoors. Some people notice the Hum only at home, while others hear it everywhere they go. Some sufferers report that it is made worse by soundproofing (e.g., double glazing), which serves only to decrease other environmental noise, thus making the Hum more apparent.​

People who both suffer from tinnitus and hear the Hum describe them as qualitatively different, and many hum sufferers can find locations where they do not hear the hum at all. An investigation by a team of scientists in Taos dismissed the possibility that the Hum was tinnitus as highly unlikely.​

Spontaneous otoacoustic emissions

Human ears generate their own noises, called spontaneous otoacoustic emissions (SOAEs), which affect between 38 percent to 60 percent of people, although the majority are unaware of these sounds.​ The people who hear these sounds typically hear a faint buzzing or ringing, especially if they are otherwise in complete silence.​ Recordings of sounds that appear to be the Hum, such as that made in Auckland, would indicate that otoacoustic emissions cannot explain all occurrences of the Hum.​

Frosch has suggested that the Hum has many properties similar to those attributed to SOAEs. The frequencies for both are audible to approximately 2% of the population and they tend to decrease during the years. They can be regarded as Van der Pol oscillators, which generate beats with neighboring external sounds, and may be located in places of extremely improved hearing abilities. Research indicates that both SOAEs and the Hum can be removed with a dose of 2.4g aspirin after the first day of medication, and that they can be eliminated during certain head rotations. He suggests that the same inner ear structures are responsible for the generation of both SOAEs and the Hum.​

Colliding ocean waves

On early June, 2008 an article published in Proceedings of the Royal Society​ announced the location of a "hum hotspot", an "energetic source area stretching from the Labrador Sea to south of Iceland, where wind patterns are especially conducive to generating oppositely traveling waves of same period, and the ocean depth is favourable for efficient microseism generation through the ‘organ pipe’ resonance of the compression waves."​ Researchers from the USArray Earthscope have tracked down a series of infrasonic humming noises produced by waves crashing together and thence into the ocean floor, off the northwest coast of the US. Potentially, sound from these collisions could travel to many parts of the globe.​​

Fish

One of the possible causes of the West Seattle Hum considered was that it was related to the Midshipman fish.​ A previous hum in Sausalito, also on the west coast of the US, was determined to be the mating call of the male Midshipman.​ However, in that case the hum was resonating through houseboat hulls and affecting the people living on those boats. In the West Seattle case, the University of Washington researcher determined that it would be impossible for any resonating hum, transmitted via tanker or boat hulls, to be transmitted very far inland; certainly not far enough to account for the reports.​

The Scottish Association for Marine Science hypothesised that the nocturnal humming sound heard in Hythe, Hampshire in the UK could be produced by a similar "sonic" fish.​ The council believed this to be unlikely because such fish are not commonly found in inshore waters of the UK.​ As of February 2014 the source had not been located, although the sound has now been recorded.​

Media coverage

The Taos Hum was featured on the TV show Unsolved Mysteries.​ It was also featured in LiveScience's "Top Ten Unexplained Phenomena", where it took tenth place.​

In popular culture

In a 1998 episode of The X-Files titled "Drive", Agent Mulder speculates that extremely low frequency (ELF) radio waves "may be behind the so-called Taos Hum".​​

See also

• List of unexplained sounds

Further reading

• «What's that noise?"». The Guardian. October 18, 2001. 
• Moorhouse, Andy; Waddington, David; Adams, Mags (February 2005). «Procedure for the assessment of low frequency noise complaints». Acoustics Research Centre, University of Salford. 
• Leventhall, Geoff. «Coping Strategies». Defra. 

• especially «Development of a course in computerised Cognitive Behavioural Therapy». (2009). 
• and «Coping Strategies for Low Frequency Noise». (2008). 

External links

• Taos Hum Homepage
• Exposure of the Hum (UK based)
• The World Hum Database and Mapping Project
• Low Frequency Noise FAQ, University of Salford
• The Science of the Hum