Infrasound

 ( Sound ) 

When Gavreau and the team attempted to measure an amplitude and pitch, they were shocked when their equipment detected no audible sound. They concluded the sound being generated by the motor was so low in pitch that it was below their biological ability to hear, and that their recording equipment was not capable of detecting these frequencies. Nobody had conceived that sound might exist at such low frequencies, and so no equipment had been developed to detect it. Eventually, it was determined that the sound inducing the nausea was a 7 cycle per second infrasound wave that was inducing a resonant mode in the ductwork and architecture of the building, significantly amplifying the sound. In the wake of this serendipitous discovery, the researchers soon got to work preparing further infrasonic tests in the laboratories. One of his experiments was an infrasonic whistle, an oversized organ pipe.Gavreau V., Infra Sons: Générateurs, Détecteurs, Propriétés physiques, Effets biologiques, in: Acustica, vol. 17, no. 1 (1966), pp. 1–10Gavreau V., infrasound, in: Science journal 4(1) 1968, p. 33Gavreau V., "Sons graves intenses et infrasons" in: Scientific Progress – la Nature (Sept. 1968) pp. 336–344 As a result of this and similar incidents, it has become routine in new architecture construction to inspect for and eliminate any infrasonic resonances in cavities and the introduction of sound-proofing and materials with specialized sonic properties.

* Natural events: infrasonic sound sometimes results naturally from severe weather, surf, , , , , , , Ice calving of , aurorae, , lightning and upper-atmospheric lightning. Nonlinear ocean wave interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, known as . According to the Infrasonics Program at NOAA, infrasonic arrays can be used to locate avalanches in the Rocky Mountains, and to detect on the high plains several minutes before they touch down.

* Animal communication: whales, elephants, , , giraffes, ,E. Von Muggenthaler: Infrasound from the okapi, invited presentation, student competition award, proceedings from the 1992 American Association for the Advancement of Science (A.A.A.S) 158th conference, 1992 , and are known to use infrasound to communicate over distances—up to hundreds of miles in Whale sound. In particular, the Sumatran rhinoceros has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the song of the humpback whale. The roar of the tiger contains infrasound of 18 Hz and lower,Work by Muggenthaler et al, also referred to in: The Secret Of A Tiger's Roar, ScienceDaily, 1 December 2000, American Institute of Physics, Inside Science News Service (1 December 2000), Retrieved 25 December 2011 and the purr of Felidae is reported to cover a range of 20 to 50 Hz.Von Muggenthaler, E., Perera, D. (2002), The cat's purr: a healing mechanism?, In review, presented 142nd Acoustical Society of America International Conference, 2001.Work by Muggenthaler et al, referred to in: David Harrison: Revealed: how purrs are secret to cats' nine lives, The Telegraph, 18 March 2001, Retrieved 25 December 2011von Muggenthaler, (2006) The Felid Purr: A Biomechanical Healing Mechanism, Proceedings from the 12th International Low Frequency Noise and Vibration Conference, pp. 189–208 It has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a aid. Infrasound also may be used for long-distance communication, especially well documented in , and . The frequency of baleen whale sounds can range from 10 Hertz to 31 kHz,

(1995). 9780125884402, Academic Press. ISBN 9780125884402

and that of elephant calls from 15 Hz to 35 Hz. Both can be extremely loud (around 117 Decibel), allowing communication for many kilometres, with a possible maximum range of around for elephants, and potentially hundreds or thousands of kilometers for some whales. Elephants also produce infrasound waves that travel through solid ground and are sensed by other herds using their feet, although they may be separated by hundreds of kilometres. These calls may be used to coordinate the movement of herds and allow mating elephants to find each other.

* Human singers: some vocalists, including Tim Storms, can produce notes in the infrasound range.

* Man-Made sources: infrasound can be generated by human processes such as and (both chemical and nuclear), or by machinery such as , and specially designed mechanical transducers (industrial vibration tables). Certain specialized loudspeaker designs are also able to reproduce extremely low frequencies; these include large-scale rotary woofer models of subwoofer loudspeaker,

(2025). 9780849350917, CRC. . ISBN 9780849350917

as well as large horn loaded, bass reflex, sealed and transmission line loudspeakers.

Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that homing pigeons use low-frequency infrasound to navigate.

From about 1,000 Hz, the dynamic range of the auditory system decreases with decreasing frequency. This compression is observable in the equal-loudness-level contours, and it implies that even a slight increase in level can change the perceived loudness from barely audible to loud. Combined with the natural spread in thresholds within a population, its effect may be that a very low-frequency sound which is inaudible to some people may be loud to others.

One study has suggested that infrasound may cause feelings of awe or fear in humans. It has also been suggested that since it is not consciously perceived, it may make people feel vaguely that odd or supernatural events are taking place.

A scientist working at Sydney University's Auditory Neuroscience Laboratory reports growing evidence that infrasound may affect some people's nervous system by stimulating the vestibular system, and this has shown in animal models an effect similar to sea sickness.

In research conducted in 2006 focusing on the impact of sound emissions from wind turbines on the nearby population, perceived infrasound has been associated to effects such as annoyance or fatigue, depending on its intensity, with little evidence supporting physiological effects of infrasound below the human perception threshold. Later studies, however, have linked inaudible infrasound to effects such as fullness, pressure or tinnitus, and acknowledged the possibility that it could disturb sleep. Other studies have also suggested associations between noise levels in turbines and self-reported sleep disturbances in the nearby population, while adding that the contribution of infrasound to this effect is still not fully understood.

In a study at Ibaraki University in Japan, researchers said EEG tests showed that the infrasound produced by was "considered to be an annoyance to the technicians who work close to a modern large-scale wind turbine".

Jürgen Altmann of the Technical University of Dortmund, an expert on , has said that there is no reliable evidence for nausea and vomiting caused by infrasound. The Pentagon considers ear-blasting anti-hijack gun — New Scientist

High volume levels at concerts from subwoofer arrays have been cited as causing lung collapse in individuals who are very close to the subwoofers, especially for smokers who are particularly tall and thin.

In September 2009, London student Tom Reid died in a club of sudden arrhythmic death syndrome (SADS) after complaining that "loud bass notes" from the club's speakers were "getting to his heart". The inquest recorded a verdict of natural causes, although some experts commented that the bass could have acted as a trigger.

Air is a very inefficient medium for transferring low frequency vibration from a transducer to the human body. Mechanical connection of the vibration source to the human body, however, provides a potentially dangerous combination. The U.S. space program, worried about the harmful effects of rocket flight on astronauts, ordered vibration tests that used cockpit seats mounted on vibration tables to transfer "brown note" and other frequencies directly to the human subjects. Very high power levels of 160 dB were achieved at frequencies of 2–3 Hz. Test frequencies ranged from 0.5 Hz to 40 Hz. Test subjects suffered motor ataxia, nausea, visual disturbance, degraded task performance and difficulties in communication. These tests are assumed by researchers to be the nucleus of the current urban legend surrounding the "brown note" and its effects. ProSoundWeb: some effects of low end (bulletin board entry by Tom Danley)

The report "A Review of Published Research on Low Frequency Noise and its Effects" contains a long list of research about exposure to high-level infrasound among humans and animals. For instance, in 1972, Borredon exposed 42 young men to tones at 7.5 Hz at 130 dB for 50 minutes. This exposure caused no adverse effects other than reported drowsiness and a slight blood pressure increase. In 1975, Slarve and Johnson exposed four male subjects to infrasound at frequencies from 1 to 20 Hz, for eight minutes at a time, at levels up to 144 dB SPL. There was no evidence of any detrimental effect other than middle ear discomfort. Tests of high-intensity infrasound on animals resulted in measurable changes, such as cell changes and ruptured blood vessel walls.

Infrasound is one hypothesized cause of death for the nine Soviet hikers who were found dead at Dyatlov Pass in 1959.

In February 2005 the television show MythBusters attempted to verify whether the "brown note" was a reality. They tested notes down to 5 Hz in frequency and up to 153 dB in sound pressure. They used a type of subwoofer used for major rock concerts, and which had been specially modified for deeper bass extension. The rumored physiological effects did not materialize. The show declared the brown note myth "busted."

In the second concert, the pieces that were to carry a 17 Hz undertone were swapped so that test results would not focus on any specific musical piece. The participants were not told which pieces included the low-level 17 Hz near-infrasonic tone. The presence of the tone resulted in a significant number (22%) of respondents reporting feeling uneasy or sorrowful, getting chills down the spine or nervous feelings of revulsion or fear.

In presenting the evidence to the British Association for the Advancement of Science, Professor Richard Wiseman 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—our findings support these ideas."

The following day, Tandy was working on his fencing foil, with the handle held in a vice. Although there was nothing touching it, the blade started to vibrate wildly. Further investigation led Tandy to discover that the extractor fan in the lab was emitting a frequency of 18.98 Hz, very close to the resonant frequency of the eye given as 18 Hz by NASA. NASA Technical Report 19770013810, Dtic.mil This, Tandy conjectured, was why he had seen a ghostly figure—it was, he believed, 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 caused the vibration of the foil.

Tandy 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. Who ya gonna call? Vic Tandy! – Coventry Telegraph