It doesn't feel like it was too long ago that I was a child at a beach, utterly fascinated by my mum having told me that if I held a seashell to my ears, I'd hear the ocean in it. You should've seen my face light up the first time I experienced this complete wonder.
Well, we are kids no more, and we no longer believe that the vast ocean lives inside the little shell in our hands. But what really is the truth behind the roaring waves you hear in there?
The shape of a seashell, specifically that of a conch shell, happens to make it a great amplifier of ambient noise.
Which is basically to say that the rushing sound one hears is in fact the noise of the surrounding environment bouncing off and being echoed by the hollow and rounded form of the shell.
Turns out, the same effect can be produced with any cavity that sound waves can bounce around in - like an empty cup or even your own hand cupped against the ear!
The reason it sounds so similar to the ocean is because the way the waves of the ocean move against the shore are characteristically similar to the way in which air flows within the cavity of the shell.
Interestingly, some people have also spent a long timed having believed the myth that the sound of a seashell is resonating the blood rushing through the blood vessels of your ear. If that were the case, the sound would vary heavily right after exercise for instance, right? But it doesn't. Because while they are audible, the sounds of the body are too subtle and get lost among the other louder noises of the surroundings.
There you have it. The whole truth and nothing but the truth. It is admittedly not nearly as magical as believing that the seashell roared because it brought along some part of the ocean with it. But I suppose, the way in which the laws of physics work together to make this world seem like a magical place is also nothing less than a marvel too, huh?