Infrasound's sound that's lower in frequency than 20 cycles per second, the normal limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear's the primary organ for sensing infrasound, but at higher levels it's possible to feel infrasound vibrations in various parts of the body. The study of such sound waves's sometimes referred to as infrasonics, covering sounds beneath 20… (More on Infrasonic)