APA Dictionary of Psychology

n. sound whose frequency is too low to be detected by human hearing, generally encompassing the range of 20 Hz to .001 Hz. The scientific study of infrasound is known as infrasonics. Able to cover long distances and circumvent or penetrate obstacles without dispersing, infrasonic waves are used by many nonhuman animals to communicate (see infrasonic communication) and have a variety of applications in geological monitoring (e.g., prediction of volcanic eruptions, detection of earthquakes). Compare ultrasound.