Low Frequency Hum in the Earth

Elephants 'hear' low-freq 'sound' sent by other elephants 20 or more miles away through the fatty deposits in the soles of their feet.

Researchers use hydrophones (often adapted from their original military use in tracking submarines) to ascertain the exact location of the origin of whale noises.[citation needed] Their methods allow them also to detect how far through an ocean a sound travels. Research by Dr. Christopher Clark of Cornell University conducted using military data showed that whale noises travel for thousands of kilometers.[23] As well as providing information about song production, the data allows researchers to follow the migratory path of whales throughout the "singing" (mating) season. One important finding is that whales in a process called the Lombard effect adjust their song to compensate for background noise pollution.[24] Moreover, there is evidence that Blue Whales stop producing foraging D calls once a mid-frequency sonar is activated, even though the sonar frequency range (1–8 kHz) far exceeds their sound production range (25–100 Hz).[2]

Prior to the introduction of human noise production, Clark says the noises may have traveled right from one side of an ocean to the other, agreeing with a thirty-year-old concept blaming large-scale shipping.[23] His research indicates that ambient noise from boats is doubling with each decade.[23] This has the effect of reducing the range at which whale noises can be heard. Environmentalists fear that such boat activity is putting undue stress on the animals as well as making it difficult to find a mate.[23]

Wiki

The Hum is a generic name for a series of phenomena involving a persistent and invasive low-frequency humming noise not audible to all people. Hums have been reported in various geographical locations. In some cases, a source has been located. A Hum on the Big Island of Hawaii, typically related to volcanic action, is heard in locations dozens of miles apart. The Hum is most often described as sounding somewhat like a distant idling diesel engine. Typically, the Hum is difficult to detect with microphones, and its source and nature are hard to localize.

The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the "Bristol Hum", the "Taos Hum", or the "Bondi Hum".[1]

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.

Other elements seem to be significantly associated with the Hum, being reported by an important proportion of hearers, but not by all of them. Many people hear the Hum only, or much more, inside buildings as compared with outdoors. Many also perceive vibrations that can be felt through the body. Earplugs are reported as not decreasing the Hum.[2]

On November 15, 2006, Dr. Tom Moir of the Massey University in Auckland, New Zealand made a recording of the Auckland Hum and has published it on the university's website.[3][4] The captured hum's power spectral density peaks at a frequency of 56 hertz.[5] In 2009, the head of audiology at Addenbrooke's Hospital in Cambridge, Dr David Baguley, said that he believed people's problems with hum were based on the physical world about one-third of the time and the other two-thirds stemmed from people focusing too keenly on innocuous background sounds.[6]
History

In Britain, the most famous example was the Bristol hum that made headlines in the late 1970s.[6] It was during the 1990s that the Hum phenomenon began to be reported in North America and to be known to the American public, when a study by the University of New Mexico and the complaints from many citizens living near the town of Taos, New Mexico, caught the attention of the media. However, in the 1970s and 1980s, a similar phenomenon had been the object of complaints from citizens, of media reports and of studies. It is difficult to tell if the Hum reported in those earlier cases and the Hum that began to be increasingly reported in North America in the 1990s should be considered identical or of different natures.[citation needed]

On June 9, 2011, it was reported that residents of the village of Woodland, England were experiencing a hum that had already lasted for over two months.[7]

This phenomenon has also been reported since 2010 throughout Windsor and Essex County in Ontario, Canada,[8] where some residents claim it to be correlated with the time of day, or week, while others seem unaffected or unable to hear it.[9] On April 20, 2012 the Canadian Government decided to officially investigate. Current suspicions are that the noise originates on Zug Island [10]

The Hum has also frustrated residents in County Kerry, Ireland.[11] This led to it being raised in the Dáil by Michael Healy-Rae, who personally heard The Hum.[12] The phenomenon was also recorded in 2012 in Seattle.[13]

BBC News:

A village in Durham is the latest place to report a strange vibrating noise - known as "the hum". Why is it such a mystery?

According to sufferers, it is as if someone has parked next to your house and left the engine running. The Hum is a mystery low frequency noise, a phenomenon that has been reported across Britain, North America and Australia in the past four decades.

There is a range of theories from farm or factory machinery to conspiracy theories such as flying saucers. And yet, "the hum" remains an unsolved case.

Woodland, a village in county Durham, is the latest place to fall victim to the noise. Some residents have reported hearing a buzzing noise like electricity or a car engine that won't go away.

"It sounds like an overhead power line with this constant humming buzz," says Kevin Fail, a 53 year-old bathroom installer who lives in the village.
Continue reading the main story
The answer

Despite research, no-one has conclusively proved the source of The Hum, although farm or factory machinery is most commonly cited
Not everyone appears to be able to hear it
Recording equipment is sometimes unable to pick it up

He said that he and his wife hear it in bed, downstairs in the house and outside in the garden, but some residents have heard nothing. Fail believes it may have something to do with a disused mine shaft in their garden.

Durham County Council says it is planning to send someone with sound monitoring equipment to the village to investigate.

There are "crackpot theories" doing the rounds about UFOs, and Fail says his daughter, whose hobby is ghost hunting, hasn't ruled out the possibility that the mine is haunted. But unlike some residents, Fail says he's not worried. "This has been happening all over the world for decades. Whatever's out there is not going to hurt you."

Another resident of the village said they had received media interest from all over the world.

"The hum" is an international phenomenon. The beach front neighborhood of Bondi in Sydney was afflicted by it two years ago. One local resident told Australia's Sunday Telegraph at the time: "It sends people around here crazy, all you can do is put music on to block it out. Some people leave fans on.''

One case that was partially solved was in Kokomo, Indiana. The source of "the hum" was located to a fan and a compressor on an industrial site, and yet even after these were turned off some people complained the noise had not stopped.

The Largs Hum in Scotland and Bristol's mystery noise in the 1970s are two of Britain's most famous cases. Often the source of the noise is never found but disappears unexpectedly.

The truth is no-one really knows the cause of "the hum", says Geoff Leventhall, a noise and vibration consultant who has advised the government on the issue.

A part of BBC News Magazine, Who, What, Why? aims to answer questions behind the headlines

Despite years working in the field, he has never heard the hum himself and has only rarely been able to pick it up on recording equipment. In one case, his recording equipment picked up a 200 hertz signal at a complainant's house that was detectable in the lab. He managed to trace the buzz to a neighbor's central heating. But this, he says, was an exception.

"Some experts say if you can't measure a noise the presumption is tinnitus," he says. "It all gets rather fraught because people say there's nothing wrong with my hearing."

"The hum" is sometimes heard in cities but is more likely to be audible in the countryside and at night, when there is less background noise. Most complainants are people aged 50-60. The most plausible causes are industrial compressors and fans or farm machinery, Leventhall says.

In the 1970s he worked with the News of the World on their campaign to discover the mystery behind "the hum". They received 800 letters from readers complaining of the phenomenon - some of them citing UFOs. But no specific explanations emerged.

In 2009, Dr David Baguley, head of audiology at Addenbrooke's Hospital told the BBC that in about two thirds of cases no external noise could be found. He believed that sufferers' hearing had become over-sensitive. "It becomes a vicious cycle. The more people focus on the noise, the more anxious and fearful they get, the more the body responds by amplifying the sound, and that causes even more upset and distress."

In the end, the solution for sufferers may be to adopt a more accepting mindset, Leventhall argues. He prepared a report for the Department for Environment, Food and Rural Affairs that suggested cognitive behavior therapy was effective in treating the symptoms. "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."

As for the source of "the hum", don't expect a breakthrough anytime soon, he says.

"It's been a mystery for 40 years so it may well remain one for a lot longer."