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Infrasound refers to extreme bass waves or vibrations, those with a frequency below the audibility range of the human ear (20 Hz to 22 kHz). Even though these waves can't be heard by us, they can be felt and have been shown to produce a range of effects in some people including anxiety, extreme sorrow, and chills. "Loud infrasound in the range of 0.5 to 10 Hz is sufficient to activate the vestibular, or balance system, in the inner ear."* Psychologist Richard Wiseman of the University of Hertfordshire thinks that the odd sensations that people attribute to ghosts may be caused by infrasonic vibrations.* He is not alone.
In 1998, Vic Tandy, experimental officer and part-time lecturer in the school of international studies and law at Coventry University, and Dr. Tony Lawrence of the psychology department wrote a paper called "Ghosts in the Machine" for the Journal of the Society for Psychical Research. They cited infrasound as the cause of apparitions seen by staff at a so-called haunted laboratory in Warwick.
Several years earlier, Tandy was working late in the "haunted" Warwick laboratory when he saw a gray thing coming for him. "I felt the hairs rise on the back of my neck," he said. "It seemed to be between me and the door, so the only thing I could do was turn and face it."* But the thing disappeared. However, it reappeared in a different form the next day when Tandy was doing some work on his fencing foil. "The handle was clamped in a vice on a workbench, yet the blade started vibrating like mad," he said. He wondered why the blade vibrated in one part of room but not in another. The explanation, he discovered, was that infrasound was coming from an extractor fan. "When we finally switched it off, it was as if a huge weight was lifted," he said. "It makes me think that one of the applications of this ongoing research could be a link between infrasound and sick-building syndrome." When he measured the infrasound in the laboratory, the showing was 18.98 hertz--the exact frequency at which a human eyeball starts resonating. The sound waves made his eyeballs resonate and produced an optical illusion: He saw a figure that didn't exist.*
Infrasonic waves can carry over long distances and are less susceptible to disturbance or interference than higher frequencies.
Infrasound may be produced by wind, by some types of earthquakes, by ocean waves, and by such things as avalanches, volcanoes, and meteors.* Elephants have the ability to emit infrasound that can be detected at a distance of 2 km. Even tigers emit infrasound.*
books and articles
Tandy V. & Lawrence, T,. (1998). The ghost in the machine. Journal of the Society for Psychical Research, 62, 360-364.
Infrasound by John D. CodyInfrasound (Vic Tandy's scientific investigation of ghosts and infrasound)
Ghost buster by Chris Arnot Guardian July 11, 2000