Infrasound

Infrasound Arrays

Graham Holliman Velocity-Coupled Infra Bass speaker design

Infrasound refers to sound waves that have a frequency below the lower limit of audibility for humans, which is typically considered to be about 20 Hz. Sounds with frequencies below this threshold cannot be heard by humans, but they can be felt as vibrations in some cases. Infrasound is produced by a variety of natural and man-made sources, including earthquakes, volcanic eruptions, thunderstorms, wind, and certain types of machinery and industrial processes.

Production and Sources

Infrasound can be generated through a variety of mechanisms. Natural events such as earthquakes, volcanic eruptions, thunderstorms, and tornadoes are significant sources of infrasound. The ocean is another source, with waves and other movements generating infrasound frequencies. Animals, including elephants and whales, use infrasound for communication over long distances, as these low-frequency sounds travel further than high-frequency sounds.

Man-made sources include explosions, machinery, and certain types of industrial equipment. Wind turbines have also been identified as a source of infrasound, leading to discussions about their impact on human health and comfort.

Detection and Measurement

Detecting and measuring infrasound requires specialized equipment. Infrasound microphones, also known as infrasonic microphones, and seismometers can detect these low-frequency sounds. These instruments are sensitive to air pressure changes and can pick up infrasound waves over long distances.

Effects on Humans and Animals

While infrasound is below the human threshold of hearing, it can still have effects on individuals. Some studies suggest that exposure to infrasound at certain levels can cause feelings of unease, anxiety, or even fear, potentially due to its association with natural disasters. There is ongoing research into the health effects of long-term exposure to infrasound, especially concerning wind turbines and industrial machinery.

Animals, particularly those that communicate using infrasound, are affected by these frequencies in various ways. For example, elephants use infrasound to communicate over long distances, and whales use it to navigate and communicate in the ocean's depths.

Research and Applications

Research into infrasound has a wide range of applications, from detecting natural disasters before they occur to studying animal communication patterns. Infrasound monitoring is used in earthquake and volcano monitoring, offering a method to detect events before they become more apparent. The military has also explored the use of infrasound for surveillance and detection purposes.

Conclusion

Infrasound occupies a unique place in the spectrum of sound, invisible to the human ear but impactful in many ways. Its study bridges disciplines from geophysics to biology, and understanding its sources, detection methods, and effects remains a vital area of research.

Infrasound Resources
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