For years, audiophiles had been hearing audible frequencies (20 Hz – 20Khz) & synthesizing the perfect sound. But there are few Secrets about Sounds that you don’t actually hear.
Infrasound is a sound that is lower in frequency than 20 Hz (Hertz), lower than the “normal” limit of human hearing. We mostly hear infrasound through our ears, but at higher levels it is possible to feel infrasound vibrations in various parts of the body. Examples of natural events that produce ultrasound include: lightning, earthquakes, volcanoes, etc.
Human ear’s ability to listen to lower frequencies decreases logarithmically. In simple language, you need very high intensity (high air pressure) of lower frequency sound to be actually heard. This intensity needs to be really high for human ears to hear something near or below 20hz.
However, 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.
Such sound waves fall under science of infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz. This frequency range has its applications too. It is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation.
Human Reactions to Infrasounds
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. Truth be told, some Movie soundtracks make use of infrasound to produce unease or disorientation in the audience. Irreversible & Paranormal Activity are among them. We often only perceive them subconsciously, and it is usually in the pits of stomachs, or in our bones.
Research by Vic Tandy suggested that an infrasonic signal of 19 Hz might be responsible for some ghost sightings. One night, Tandy was working 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.
Although there was nothing touching fencing foil, 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. 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 center, thus causing a standing wave which was detected by the foil.
Tandy’s research led to the removal of many doubts humans had about haunted houses. 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.
Sounds play with human emotions, when we hear them and when we don’t. 16Hz is the sweet spot, when produced from a high quality Amp and Woofers. One would hear the deepest Bass with a frequency that resonates your bones and/or the brain. The feeling is immense, the experience is amplified by several multipliers. Most of the High-end Home theaters and even IMAX grade theaters would have it. Else, check it out with an audiophile, your woofers probably won’t do it.