- Mistpouffers: Mistpouffers are unexplained reports that sound like a cannon or a sonic boom. They have been heard in many waterfront communities around the world such as the banks of the river Ganges in India, the East Coast and inland Finger Lakes of the United States, as well as areas of the North Sea, Japan and Italy; and sometimes away from water. Names differ according to area
- Helmholtz resonance (sound of blowing over bottle)
Unsettling effects of Infrasound
The film "irreversible" uses extremely low-frequency sound during the opening twenty to thirty minutes to create a state of disorientation and unease in the audience, including the nine minute rape scene.
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. 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.
The Ghost in the Machine
Research by Vic Tandy, a lecturer at Coventry University, suggested that the frequency 19 Hz 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, the blade 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 (given as 18 Hz in NASA Technical Report 19770013810). 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.
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.