We’re told a number of stories as kids. There’s the one about pulling a face for too long and having it stick that way, or the myth that Australian toilets flush backwards; some of us are even cruelly told that Santa isn’t real, despite ample evidence to the contrary.
One of the more harmless of these little lies is the one about seashells. You know the one: hold up a seashell to your ear, and you can hear the sea, no matter how far inland you currently are. Somehow, those inanimate little nautili and abandoned critter cribs hang onto the sounds from their one-time homeland, just waiting for a passing human to listen in and hear the whispering of the ocean current.
Of course, objectively, this can’t be true – not unless somebody is going around sticking tiny speakers inside all the seashells in the world, at any rate. Yet, it’s also one of the more believable urban legends – for the simple reason that it, well, works.
It’s true: hold up a shell to your ear, and you really will hear something akin to the ocean swirling around inside it. So, what's actually going on here – and if that’s not the sea we’re hearing, what is it?
The stories you’ve probably been told
No doubt some of our readers are already confidently asserting that they know the answer – and indeed, there are one or two supposedly scientific explanations for the phenomenon that you’ve probably heard.
“One popular (but wrong) explanation is that you are listening to your own blood coursing through you,” wrote Karl Kruszelnicki, the Australian science communicator better known as “Dr Karl”, back in 2012.
There’s a way in which this makes sense: after all, when we lie on a pillow, we can hear our blood pulsing in our head, Kruszelnicki pointed out. The hypothesis has some big-name supporters, too: even Carl Sagan got behind the idea, writing in 1973 that “Everyone knows the ‘sound of the sea’ to be heard when putting a seashell to one’s ear. It is really the greatly amplified sound of our own blood rushing.”
However, as popular as this theory is, it’s surprisingly easy to disprove. “Press your ear to a shell and listen, then run around on the beach for a few minutes to increase the blood flow all through your body, and again listen to your magic shell,” Kruszelnicki wrote. “You'll find that the loudness of the ‘sound of the sea’ is still the same.”
If we truly were hearing the sound of our blood rushing through our bodies, that wouldn’t be the case: exercising makes your blood pressure and pulse increase, which would thus intensify the supposed sounds being “reflected” by the shell. The fact that we don’t hear a difference before and after exerting ourselves, therefore, means one thing: the “blood” theory just doesn’t hold water.
If not the red stuff, perhaps it’s some other inner fluid we’re hearing? We know that our inner ears are constantly sloshing with endolymph and perilymph fluids – it’s what keeps us upright, after all. Maybe, then, it makes sense that holding a shell to the outside of the organ would be somehow amplifying the noise of that liquid, rather than the ocean, and reflecting it back at our listening holes.
Yet, again, this fails a simple experiment: our inner ear fluid is in motion whenever we move our heads, implying that any seashell sounds would change depending on the angle and direction we’re facing. If cocking your head to the side doesn’t result in an auditory mini-tidal wave, it stands to reason that this isn’t what causes the phenomenon either.
Finally, there’s the idea that the “sea” you can hear in a shell is actually air – air flowing through the shell and out again, which creates the signature whooshing, flowing noise.
It’s harder to disprove than the others, because it needs some pretty specialist equipment – specifically, an anechoic chamber, or a completely soundproof room. There’s air flow in these rooms, so they shouldn’t affect any airflow around the shell itself – and yet, scientists have repeatedly found that holding a seashell to your ear in one produces a strangely silent result.
“You won't hear anything in a completely soundproofed room,” confirmed Andrew King, director of the University of Oxford's Centre for Integrative Neuroscience and head of the Oxford Auditory Neuroscience Group, speaking to Live Science last year. “Background noise must be present.”
That’s the biggest clue as to what’s really going on here: the sounds we hear “inside” seashells are not coming from inside our bodies, but rather around them.
“You are hearing ambient or background noise that has been increased in amplitude by the physical properties of the seashell,” King explained. It "acts as a resonator, boosting certain sound frequencies, so that they are louder than they would be without the seashell placed next to your ear.”
The specific sounds we hear within a conch or a nautilus depend on the exact shape of the shell itself, he explained: the hard, curved surfaces inside the shell cause the sound waves that enter to bounce around, amplifying some frequencies while dampening others.
Precisely which frequencies are amplified is also important. “The sounds seashells ‘catch’ tend to be what scientists call lower-frequency sounds. Think of these as deeper, or more rumbling sounds,” wrote Chris Brennan-Jones, Head of Ear Health at Curtin University’s Telethon Kids Institute, in a 2022 article for The Conversation.
“The sound of the ocean is also a low-frequency sound,” he continued. “That’s why it sounds similar to the sounds caught in a shell.”
Seashells may be the most poetic of ways to experience this resonance, but they’re definitely not the only method – pretty much any convex surface will do. If you’re in the kitchen, rather than on a beach, you can try holding a teacup or a bowl to your ears, for example; even your own cupped hands can achieve the same effect, albeit to a smaller degree.
In fact, even the natural shape of our ears themselves can be seen as a minor example of this phenomenon.
Of course, should you try this experiment in the kitchen, the sound you hear in your makeshift “shell” will be different from what you hear in a conch next to the sea. That’s for two big reasons: the size and shape of the cup or bowl versus the shell, and the ambient noise – because the soundscape of a kitchen, formed from the buzz of a refrigerator and the hum of water pipes, is quite different from the open ocean.
This rather brings us full circle, doesn’t it? After all, if the sound inside seashells is in fact the ambient noise around us, then really – as long as you stay near the sea itself – it actually is the ocean you can hear in there after all.