Do you believe in ghosts? The hallmark signs of a haunted house—mysteriously blown out candles, creepy sensations, and unexplainable feelings of uneasiness—might actually be produced by something called infrasound, according to British scientists.
Infrasound: What Is It?
Infrasound, by definition, is sound lower in frequency than 20 hertz, which is considered the normal limit of human hearing. It is sometimes called low-frequency sound, and it is very difficult for humans to hear. Experiments have shown that infrasound can produce a wide and strange range of effects in those who experience it, including anxiety, shivers, and extreme sorrow. Generally, humans cannot consciously perceive infrasound, but they can feel it. In the British study, researchers played music laced with infrasound for test subjects, and 22 percent reported feelings of uneasiness, revulsion, or fear after listening.
Infrasound can be caused by many different sources—storms, winds, earthquakes, animals, and even wind turbines can produce infrasound. Elephants use infrasound to communicate over long distances; since low frequency sounds travel farther than high frequency ones, infrasound is ideal for communicating from far away. These communications, or “rumbles,” were discovered by a researcher who felt, rather than heard, the elephants rumbling to each other. The discovery of elephant rumblings offers a solution to the question of how elephant families are able to coordinate patterns of movement when separated, and how males find far-away females for breeding. Whales also use infrasonic sound, and have been observed communicating with each other over distances of hundreds of miles.
Studies have also suggested that animals can perceive infrasound before a natural disaster hits. Hours before the 2004 Indian Ocean tsunami, animals fled the coastal areas, and many researchers believe it was due to the presence of infrasound. Animals might also use infrasound as a navigational device. A study of homing pigeons in 2013 discovered that the birds used infrasound, generated by miniscule vibrations of the earth’s surface deep in the ocean, as a tool to find their bearing home.
Infrasound and Hearing Loss
Infrasound affects the ear in several ways. Infrasound can disturb the sensory cells inside your ear and change their sensitivity, according to research done by Washington University of St. Louis. Infrasound may cause subconscious pathways of hearing, causing you to wake up from sleep, even though there hasn’t been any audible noise. It is suspected that infrasound can possibly cause endolymphatic hydrops, which is when a liquid-filled compartment in the ear swells suddenly, causing vertigo, tinnitus, and more. It is unconfirmed for humans, but long exposure to very low frequency sounds may even cause noise-induced hearing loss.
How else does infrasound affect humans? Besides causing odd or discomforting feelings, infrasound may have physical effects as well. There have been several studies examining the infrasound produced by wind turbines and how they affect people who live too close. Wind turbines cause infrasound that can travel through the atmosphere for hundreds of miles, and may cause breathing and digestive problems.
There are no devices to protect your ears from infrasound, but it is unlikely you will be exposed to large amounts. Avoid living near volcanoes or wind turbines, and you shouldn’t have any problems with infrasound!