infrasound

thumb|upright=1.5|Infrasound arrays at a monitoring station in Qaanaaq, [[Greenland]]

Infrasound, sometimes referred to as low frequency sound or (sometimes ambigously) subsonic (subsonic being a descriptor for "less than the speed of sound"), describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz, as defined by the ANSI/ASA S1.1-2013 standard). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body.