Acoustic waves with very low frequencies are called infrasound. In fact, these waves are below the frequency band audible to the human ear, which typically ranges from 20 to 20,000 Hertz. Infrasound is produced by a variety of natural and man-made sources: exploding volcanoes, earthquakes, meteors, storms and auroras in the natural world; nuclear, mining and large chemical explosions, as well as aircraft and rocket launches in the man-made arena.