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soundlike waves having a frequency below the audible range, that is, below about 16Hz
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


Sound waves, particularly in the atmosphere, whose frequencies of pressure variation and of vibration are below the audible range, that is, lower than about 20 Hz. Earthquake and seismic waves are elastic waves which occur at infrasonic frequencies in the Earth's crust and in the oceans and seas. The physical laws of propagation in the atmosphere are essentially the same as for audible sound. The local speed of infrasound in air at ambient temperatures near 20°C (68°F) is about 340 m/s (1115 ft/s), the same as for audible sound.

At frequencies less than about 1.0 Hz, infrasound propagates through the atmosphere for distances of thousands of kilometers without substantial loss of energy. Sounds at these frequencies are almost always present at measurable intensities. Those of natural origin have many causes, including tornadoes, volcanic explosions, earthquakes, the aurora borealis, waves on the seas, large meteorites, and lightning discharges. When the wind blows, turbulent pressure fluctuations in the atmosphere occur at amplitudes up to tens of pascals, at infrasonic frequencies. People are unaware of these pressures via the sensation of hearing.

Sufficiently strong infrasound is “audible,” contrary to simple acoustic tradition. The threshold sound pressure level (the least intensity for audibility) is about 92 dB at 16 Hz, and increases 12 dB per octave to about 140 dB at 1.0 Hz. However, there is no sensation of tone. Listeners variously describe audible infrasound as pumping, popping effect, or chugging. For vibration at very low frequencies, motion sickness of people in boats must have been one of the earliest noticeable effects. The human body is particularly sensitive to vibrations and infrasound near 7 Hz, at which frequency there is an overall mechanical resonance of organs in the abdominal and chest cavities. See Atmospheric acoustics, Sound

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



elastic waves similar to sound waves but at frequencies below those audible to humans. The upper limit of the infrasonic region is usually assumed to be 16—25 hertz (Hz). The lower limit of the infrasound range is indefinite. Vibrations of tenths and even hundredths of a hertz—that is, with periods dozens of seconds long—are of practical interest. Infrasound exists in the noises of the atmosphere, the forests, and the seas; its source is atmospheric turbulence and wind (for example, the so-called voice of the sea is infrasonic vibrations created by the wind vortices on the crests of ocean waves). Infrasonic vibrations are also produced by lightning discharges (thunder), explosions, and gunfire.

Tremors and vibrations at infrasonic frequencies are observed in the earth’s crust from a great variety of sources including explosions, avalanches, and transportation.

The absorption of infrasound in various mediums is typically small, so that infrasonic waves in air, water, and the earth’s crust can propagate over great distances. This phenomenon is of practical use in locating strong explosions or the position of guns that are firing. The long-range propagation of infrasound in an ocean makes possible the prediction of natural calamities, such as tsunamis. The sounds of explosions, which contain a large number of infrasonic frequencies, are used to study the upper atmospheric layers and the properties of the aqueous medium.

Infrasound is received and measured by means of special microphones, hydrophones, geophones, or vibrometers.


Shuleikin, V. V. Fizika moria, 4th ed. Moscow, 1968.
Cole, R. Podvodnye vzryvy. Moscow, 1950. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Vibrations of the air at frequencies too low to be perceived as sound by the human ear, below about 15 hertz.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


Acoustic oscillations having a frequency below the low-frequency limit (approximately 16 Hz) of audible sound.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


Infrasonic refers to sound below the audible hearing range; typically under 20 Hz. Contrast with ultrasonic.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
References in periodicals archive ?
"Comments on recently published article, 'Concerns about infrasound from wind turbines.'" Acoustics Today 9(4).
National Library of Medicine, was the source of this peer-reviewed literature and the search terms used were as follows: (1) "Infrasound AND Health Effects"; (2) "Low-Frequency Noise AND Health Effects"; (3) "Low-Frequency Sound AND Health Effects"; (4) "Wind Power AND Noise"; (5) "Wind Turbines"; (6) "Wind Turbines AND Noise."
It has been suggested that infrasound explains the feeling of a 'haunting'--that clinging feeling of doom or fear, or the feeling that something is there.
The state Departments of Environmental Protection and Public Health have since convened an expert panel to explore the effects of infrasound and other potential turbine health risks.
Infrasound: Sensors measure very small changes in atmospheric
Brown, a professor of meteor physics at the University of Western Ontario, said the energy estimate derived from infrasound records indicated that the asteroid fragment weighed approximately 10 tonnes when it entered the atmosphere.
Readers who like fast-moving thrillers with a sci-tech angle don't need to have read the first in the series to enjoy this entry, which features lots of action and puts forward some intriguing scientific theories: e.g., could infrasound and breezes be responsible for "hauntings"?
Some specific topics include debris flow mitigation with flexible ring net barriers, infrasound measurements of debris flow, numerical modeling of transient flows with high sediment concentrations, and the role and management of in-channel wood in relation to flood events in Southern Andes basins.
Organizations have their own unique infra-sound and leaders must listen to this infrasound in their organization to avoid losing their orientation.
Elephants, whales, hippos, rhinos, alligators, and giraffes also communicate with a low frequency sound called infrasound. Infrasonic calls can travel effectively for miles though air, land and water to the animal's family members.
They will run tests with low-level sound - known as infrasound - which is said to be associated with haunting experiences.