Humans A Human can hear frequencies that range from 20Hz to 20,000Hz. Sounds are made by something moving backwards and forwards. This is called Vibrating When a man speaks his vocal cords vibrate this makes the sound travel, so when someone else picks up the vibration they can then hear what they are saying. Sound waves travel through the air and into the ear, making the eardrum vibrate. These vibrations then cause the 3 small bones in the ear to vibrate and these in turn cause the liquid inside the cochlea to vibrate.
Dolphins Today we know that dolphins produce clicks using nasal sacs. The sounds reflect off objects and are picked up again in the dolphins lower Jaw The reflected sound waves travel through a channel filled with fat and then into the ear. Like light waves, sound waves can be focused, and dolphins have a “lens” made of fat that they use to focus on sound waves. Sound waves that have a frequency above 20,000hz (the upper limit of human hearing) are called ultrasound. However dolphins are only known to emit sound waves within frequencies up to about 150 kHz where as ultrasound use waves of 1-20mhz.