Dolphins do not have external ears, but they can hear through a sophisticated hearing sense located in two small openings on both sides of the head.
However, scientists believe that dolphins hear underwater through the lower jaw bone which conducts sounds to the middle ear.
Dolphins can listen to a broader range of frequencies than humans.
While we can hear sounds from 20 Hz to 20 kHz, dolphins can hear from 20 to 150 kHz being up to 7 times more sensitive their hearing sense than the human ear.
Therefore we are not able to listen to a significant number of sounds made by dolphins.