Have you ever visited the ocean? Maybe you live along a coastline where you get to see the ocean all the time. For most others, though, seeing the ocean means taking a trip — sometimes a long trip! — to visit the ocean.

If you’ve ever walked along a seashore, you’ve probably searched for seashells. They’re not always easy to find, though. If you can’t find any big seashells, you may decide to check out the selection of shells at a local souvenir shop.

One thing most children do upon first picking up a large seashell is to hold it up to their ears to listen for the sounds of the ocean inside the shell. If you’ve ever tried this, you know that it works. No matter how far you are from the ocean, it seems like you can hear the soothing sounds of ocean waves lapping up onto the beach when you hold a shell to your ear.

Obviously, the ocean isn’t inside the shell. So what exactly is it that you’re hearing? If not the ocean, what in the world is it?

One popular myth that many people believe is that, when you hold a shell up to your ear, what you’re really hearing is the echo of the blood pumping through the blood vessels in your head. It sounds believable, but scientists have proved that the echo of pumping blood is not what you’re hearing.

Others believe what you hear is the sound of air flowing through the shell. Scientists have disproved this theory, too, though. When tested in a soundproof room — where there’s still air flowing — shells don’t produce the same “ocean” sound.

So what IS that sound you hear? Scientists believe the most likely answer is that it’s the echo of the noise in the air around you. They call this ambient noise. The seashell captures the ambient noise, which then resonates inside the shell.

Depending upon the size and type of shell you listen to, different frequencies of sound will be echoed back to your ear. This leads to different shells making different “ocean” sounds. The best shells are large, spiral conch shells.

Would you believe you don’t even need a shell to hear the “ocean”? You can produce the same effect with an empty cup or simply by cupping your hand over your ear. You may want to try this in a noisy area. The more ambient noise there is around you, the louder the effect will be.