(as per Wikipedia)
20 Hz is considered the normal low frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz.[15] Below 10 Hz it is possible to perceive the single cycles of the sound, along with a sensation of pressure at the eardrums.
The dynamic range of the auditory system decreases with decreasing frequency. This compression can be seen in the equal-loudness-level contours, and it implies that 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, it may have the effect that a very low frequency sound which is inaudible to some people may be loud to others.
Infrasound has been known to cause feelings of awe or fear in humans. Since it is not consciously perceived, it can make people feel vaguely that supernatural events are taking place. "Infrasound linked to spooky effects". msnbc.com. 2007-09-07. http://www.msnbc.msn.com/id/3077192/. Retrieved 27 January 2010.
Some film soundtracks make use of infrasound to produce unease or disorientation in the audience. Irréversible is one such movie.
The infrasound and low-frequency noise produced by some wind turbines is believed to cause certain breathing and digestive problems in humans and other animals in close proximity to the turbines.[16]
[edit] Infrasonic 17 Hz tone experiment
On May 31, 2003, a team of UK researchers held a mass experiment where they exposed some 700 people to music laced with soft 17 Hz sine waves played at a level described as "near the edge of hearing", produced by an extra-long stroke sub-woofer mounted two-thirds of the way from the end of a seven-meter-long plastic sewer pipe. The experimental concert (entitled Infrasonic) took place in the Purcell Room over the course of two performances, each consisting of four musical pieces. Two of the pieces in each concert had 17 Hz tones played underneath. 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 anxiety, uneasiness, extreme sorrow, nervous feelings of revulsion or fear, chills down the spine and feelings of pressure on the chest.[17][18] In presenting the evidence to 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."[19]
[edit] The Ghost in the Machine
Research by Vic Tandy, a lecturer at Coventry University, suggested that an infrasonic signal of 19 Hz might be responsible for some ghost sightings. Tandy 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 Tandy turned to face the grey blob, there was nothing.
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.[20] This was why Tandy had seen 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.[21]
Tandy investigated this phenomenon further and wrote a paper entitled The Ghost in the Machine[22]. Tandy 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[23][24] and Edinburgh Castle.[25][26]
References:
1. ^ "Gavreau", in Lost Science by Gerry Vassilatos. Signals, 1999. ISBN 0-932813-75-5
2. ^*Gavreau V., Infra Sons: Générateurs, Détecteurs, Propriétés physiques, Effets biologiques, in: Acustica, Vol .17, No. 1 (1966), p.1–10
3. ^ Gavreau V.,infrasound,in: science journal 4(1) 1968,S.33
4. ^ Gavreau V., "Sons graves intenses et infrasons" in: Scientific Progres – la Nature (Sept. 1968) p. 336–344
5. ^ Garces, M.; Hetzer C., Merrifield M., Willis M. and Aucan J. (2003). Observations of surf infrasound in Hawai’i. http://www.agu.org/pubs/crossref/2003/2003GL018614.shtml. Retrieved 2007-12-15. "Comparison of ocean buoy measurements with infrasonic array data collected during the epic winter of 2002–2003 shows a clear relationship between breaking ocean wave height and infrasonic signal levels.".
6. ^ Garces, M.; Willis, M. (2006). Modeling and Characterization of Microbarom Signals inthePacific. http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA456958. Retrieved 2007-11-24. "Naturally occurring sources of infrasound include (but are not limited to) severe weather, volcanoes, bolides, earthquakes, surf, mountain waves, and, the focus of this research, nonlinear ocean wave interactions.".
7. ^ Haak, Hein (2006-09-01). "Probing the Atmosphere with Infrasound : Infrasound as a tool" (pdf). CTBT: Synergies with Science, 1996–2006 and Beyond. Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization. http://www.ctbto.org/reference/symposiums/2006/haak/0901probingtheatmosphere.pdf. Retrieved 2007-11-24.
8. ^ "Microbaroms". Infrasonic Signals. University of Alaska Fairbanks, Geophysical Institute, Infrasound Research Group. http://www.gi.alaska.edu/infrasound/Infrasound254.htm. Retrieved 2007-11-22. "The ubiquitous five second period infrasonic signals called “microbaroms”, which are generated by standing sea waves in marine storms, are the cause of the low-level natural-infrasound background in the passband from 0.02 to 10 Hz."
9. ^ Chen, C.H., ed (2007). Signal and Image Processing for Remote Sensing. Boca Raton: CRC. pp. 33. ISBN 0-8493-5091-3.
10. ^ Goddard Space Flight Center[dead link]
11. ^ "How did animals survive the tsunami?" Christine Kenneally, December 30, 2004. Slate Magazine
12. ^ Nature . Can Animals Predict Disaster? - PBS: posted November 2005.
13. ^ Langbauer, W.R.; Payne, K.B.; Charif, R.A.; Rapaport, L.; Osborn, F. (1991). "African elephants respond to distant playbacks of low-frequency conspecific calls". Journal of Experimental Biology 157 (1): 35–46. http://jeb.biologists.org/cgi/reprint/157/1/35.pdf. Retrieved 2009-05-27
14. ^ Larom, D.; Garstang, M.; Payne, K.; Raspet, R.; Lindeque, M. (1997). "The influence of surface atmospheric conditions on the range and area reached by animal vocalizations". Journal of experimental biology 200 (3): 421–431. http://jeb.biologists.org/cgi/reprint/200/3/421.pdf. Retrieved 2009-05-27
15. ^ Olson, Harry F. (1967). Music, Physics and Engineering. Dover Publications. p. 249. ISBN 0486217698. http://books.google.com/?id=RUDTFBbb7jAC.
16. ^ HowStuffWorks. Do wind turbines cause health problems?
17. ^ Infrasonic concert, Purcell Room, London, 31 May 2003, sponsored by the sciart Consortium with additional support by the National Physical Laboratory (NPL)
18. ^ Sounds like terror in the air Sydney Morning Herald, September 9 2003.
19. ^ "Infrasound linked to spooky effects". msnbc.com. 2007-09-07. http://www.msnbc.msn.com/id/3077192/. Retrieved 27 January 2010.
20. ^ NASA Technical Report 19770013810
21. ^ infrasound
22. ^ Tandy, V.; Lawrence, T. (April 1998). "The ghost in the machine.". Journal of the Society for Psychical Research 62 (851): 360–364. http://www.psy.herts.ac.uk/ghost/ghost-in-machine.pdf.
23. ^ Tandy, V. (July 2000). "Something in the cellar.". Journal of the Society for Psychical Research 64.3 (860). http://www.psy.herts.ac.uk/ghost/Something-in-the-Cellar.pdf.
24. ^ Arnot, Chris (2000-07-11). "Ghost buster". The Guardian (London). http://www.guardian.co.uk/Archive/Article/0,4273,4038891,00.html. Retrieved 2010-05-05.
25. ^ Who ya gonna call? Vic Tandy! - Coventry Telegraph
26. ^ Internet Archive Wayback Machine. 2007 version of Vic Tandy's Ghost Experiment webpage
• "infrasound". Collins English Dictionary, 2000. Retrieved 25 October 2005, from xreferplus. http://www.xreferplus.com/entry/2657949
• Gundersen, P. Erik. The Handy Physics Answer Book. Visible Ink Press, 2003.
• Chedd, Graham. Sound; From Communications to Noise Pollution. Doubleday & Company Inc, 1970.
• O'Keefe, Ciaran, and Sarah Angliss. "The Subjective Effects of Infrasound in a Live Concert Setting". CIM04: Conference on Interdisciplinary Musicology. Graz, Germany: Graz UP, 2004. 132–133.
• Discovery's Biggest Shows aired at 8:00 pm (Indian Standard Time) on The Discovery Channel, India on Sunday, 7 October 2007
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