There’s a reason people compare garbled voicemails to listening to someone talk underwater—our ears just aren’t built for a watery world. But animals like whales and dolphins use sound all the time to hunt down dinner or to serenade a mate. Now, new research is highlighting just how marine mammals evolved to listen underwater.
Sound is basically vibrations in the air or water that people or animals perceive as noise, right?
So why can’t we hear underwater?
We can hear underwater, we just can’t hear well. Our ears are designed for hearing in air. We have an air-filled ear canal—at the end there is an eardrum that vibrates in response to sound, which sets up a chain reaction of movement in the ear bones. The vibrations are translated to the inner ear, where the mechanical energy is translated to electrical pulses to the brain.
Underwater, our whole skull vibrates in response to sound and so both of our ears are affected at the same time. And what that means is that it’s really hard to figure out where that sound is coming from.
How does having our head vibrate keep us from localizing sound?
When your whole skull is vibrating—the bones housing your middle and inner ear are integrated into your skull—both of your ears are vibrating with the skull. That doesn’t happen in air.
In whales, the bones housing the middle and inner ears are separated from the skull, and that’s part of the mechanism that isolates each ear from each other and from the skull, and they’re able to figure out where sounds are coming from much better.source : http://news.nationalgeographic.com/2015/03/150311-whales-hearing-underwater-ears-echolocation-ocean-animals-science/