What is Infrasound?
Infrasound is sound with a frequency too low to be detected by humans. These range from about 17 to 16 hertz, the limits of human hearing, to as low as 0.001 hertz. A sound wave that is 1 hertz has a period of one second. The range of human audibility is around 20 to 20,000Hz, with women capable of hearing slightly higher frequencies, an ability which decreases with age. Numerous animals, including whales, elephants, rhinoceros, giraffes, okapi, and alligators, communicate using infrasound. Infrasound can be thought of as a slow, periodic rumbling – it is generated by large processes such as avalanches, volcanoes, tornadoes, ocean waves, earthquakes, and meteors. It can be generated by large chemical or nuclear explosions. Because it is one of the telltale signs of nuclear testing, infrasound is continuously monitored worldwide by the Comprehensive Nuclear-Test-Ban Treaty Organization. Infrasound can give humans a feeling of unease or awe. It is thought that ambient ultrasound, sound t
geoff@activenoise.co.uk Definitions of infrasound and low-frequency noise are discussed and the fuzzy boundary between them described. Infrasound, in its popular definition as sound below a frequency of 20 Hz, is clearly audible, the hearing threshold having been measured down to 1.5 Hz. The popular concept that sound below 20 Hz is inaudible is not correct. Sources of infrasound are in the range from very low-frequency atmospheric fluctuations up into the lower audio frequencies. These sources include natural occurrences, industrial installations, low-speed machinery, etc. Investigations of complaints of low-frequency noise often fail to measure any significant noise. This has led some complainants to conjecture that their perception arises from non-acoustic sources, such as electromagnetic radiation. Over the past 40 years, infrasound and low-frequency noise have attracted a great deal of adverse publicity on their effects on health, based mainly on media exaggerations and misunderst
