Infrasound sometimes referred to as low-frequency sound, lower in frequency than 20 Hz or cycles per second of the “normal“ limit of human hearing (20 kHz). Infrasound is characterized by an ability to get around obstacles with little dissipation.

The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.1 Hz and rarely to 0.001 Hz. This frequency range can be used for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart.

Infrasounds interest the field of phonotelemetry, in relation to the low frequency components present in the gunshot wave, the field of impulsive noises, for the same reason, and above all the field of vibrometry, since the elastic waves propagating in building structures have the fundamental component in the infrasound field; this problem closely concerns anti-seismic constructions. Infrasound surveying is performed using microphones sensitive to quasi-continuous pressures, such as piezoelectric and electret microphones.