I remember when I was a young boy and my mom had me listen to a souvenier conch shell. I was amazed! It sounded just like the ocean waves, crashing on the beach. But I was sitting on the couch at our house, 75 miles from the ocean!
So, what causes this illusion?
One theory is that it’s caused by your own blood going through your ear. But if you do an experiment, you will see that this is not true. Just run for awhile, get the heart rate up, and listen to your sea shell. You’ll notice no difference in the sound than before you ran. So, that’s not it.
Another theory says the sound of waves are caused by the air flowing through the shell. But if you test this out in a sound-proof room (where it is dead-quiet), holding the sea shell to your ear, there is no sound of waves.
This last experiment leads us to the most likely explanation – the wave sound is actually the background noise in the area around you. The shell has hollow chambers that allow sound to resonate around, inside the shell.
You don’t even need the seashell to hear the same type of noise. You can produce the same ‘ocean-waves’ sound using an empty cup over your ear. Try it yourself. Vary the distance you place the cup near your ear. The level of the sound will vary depending on the angle and distance the cup is from your ear. The louder the background noise in the environment, the louder the ocean-like sound will be.