Below 20 Hz, above 20 kHz

Most adults can hear from about 20 Hz to 16-17 kHz (children up to ~20 kHz). Outside that band, fascinating sound still exists.

• Infrasound (<20 Hz): elephant calls, ocean storms, earthquakes - felt rather than heard, can travel huge distances.
• Ultrasound (>20 kHz): bat echolocation, medical imaging (sonograms), industrial cleaners, dog whistles.