When you hold a shell to your ear, suddenly, there's the ocean! But the sounds you hear in a shell actually have nothing to do with the ocean. They are sipmly the sounds around you and inside your ear.
The noise around you is made louder by the vibration of the air in the shell. The air molecules are bumping into each other. What you hear just sounds like the waves of the ocean.You can hear the same thing in an empty can or even a cup. That's not the sound of the ocean, either but the vibration of air inside your ear, says 3-2-1- Contact magazine.
When you control that vibration, you can make beautiful music. Much the same kind of vibration takes place in musical instruments. When you strum a guitar, for instance, the strings vibrate. The sound waves pass through the wood to the air trapped inside the guitar. The air vibrates, making the sound greater. It's music to your ears.