Infrasound

Infrasound is sound with a frequency too low to be detected by the human ear. The study of such sound waves is sometimes referred to as infrasonics, covering sounds from the lower limit of human hearing (about 16 or 17 hertz) down to 0.001 hertz. This frequency range is the same one that seismographs use for monitoring earthquakes. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation.

About infrasound
Possibly the first observation of naturally-occurring infrasound was in the aftermath of the Krakatoa eruption in 1883, when concussive acoustic waves circled the globe seven times or more and were recorded on barometers worldwide.

One of the pioneers in infrasonic research was French scientist Vladimir Gavreau, born in Russia as Vladimir Gavronsky. His interest in infrasonic waves first came about in his lab during the 1960s where he and his lab assistants experienced pain in the ear drums and shaking lab equipment, but no audible sound was picked up on his microphones. He concluded it was infrasound and soon got to work preparing tests in the labs. One of his experiments was an infrasonic whistle.

Infrasound sometimes results naturally from ocean waves, avalanches, earthquakes, volcanoes, and meteors. Infrasound can also be generated by man-made processes such as explosions, both chemical and nuclear. The Comprehensive Nuclear-Test-Ban Treaty Organization uses infrasound as one of its monitoring technologies (along with seismic, hydroacoustic, and atmospheric radionuclide monitoring).

Whales, elephants, hippopotamuses, rhinoceros, giraffes, okapi, and alligators are known to use infrasound to communicate over varying distances of up to many miles, as in the case of the whale. It has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a navigational aid.

Scientists discovered by accident that the spinning core or vortex of a tornado creates infrasonic sounds. When the vortices are large, the frequencies are lower; smaller vortices have higher frequencies. These infrasonic sound waves can be detected for up to 161km (100 miles) away, and so can help provide early warning of tornadoes.

Animal and human reactions to infrasound
Concerning behavioral patterns of animals and the infrasonic effects of natural disasters, it is to be noted that animals can also recognize the infrasonic waves emitted from such natural disasters and can use these as an early warning. A recent example of this is the 2004 Indian Ocean earthquake. Animals were reported to flee the area long before the actual tsunami hit the shores of Asia. It is not known for sure if this is the exact reason, as some have suggested that it was the influence of electromagnetic waves, and not of infrasonic waves, that prompted these animals to flee.

It has long been realized that infrasound may cause feelings of awe or fear. Since it is not consciously perceived, it can make people feel vaguely that supernatural events are taking place. In a controlled experiment published in September, 2003, people at a concert were asked to rate their responses to a variety of pieces of music, some of which were accompanied by infrasonic elements. The participants were not aware of which pieces included the infrasound. Many participants (22%) reported feelings of anxiety, uneasiness, extreme sorrow, nervous feelings of revulsion or fear and chills down the spine which correlated with the infrasonic events. In presenting the evidence to the BA, the scientist responsible said "These results suggest that low frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound. Some scientists have suggested that this level of sound may be present at some allegedly haunted sites and so cause people to have odd sensations that they attribute to a ghost&mdash;our findings support these ideas".

Some film soundtracks also make use of infrasound to produce unease or disorientation in the audience. Irréversible is one such movie.

In music, Brian "Lustmord" Williams is known to utilize infrasound to create these same feelings.

Source of ghosts
Research by Vic Tandy, a lecturer at Coventry University, suggested that the frequency 19 hertz was responsible for many ghost sightings. He was working late one night alone in a supposedly haunted laboratory at Warwick, when he felt very anxious, and could detect a grey blob out of the corner of his eye. When he turned to face it, there was nothing.

The following day, he was working on his fencing foil, with the handle held in a vice. Although there was nothing touching it, it started to vibrate wildly. Further investigation led him to discover that the extraction fan was emitting a frequency of 18.98 Hz, very close to the resonant frequency of the eye. This was why he saw a ghostly figure - it was an optical illusion caused by his eyeballs resonating. The room was exactly half a wavelength in length, and the desk was in the centre, thus causing a standing wave which was detected by the foil.

Vic investigated this phenomenon further, and wrote a paper entitled The Ghost in the Machine. He carried out a number of investigations at various sites believed to be haunted, including the basement of the Tourist Information Bureau next to Coventry Cathedral and Edinburgh Castle