Mental Floss

Why Do Shells Sound Like the Ocean?

You don’t need to be at the beach to hear what sounds like crashing waves.
ByMatt Soniak|
It’s an aural illusion.
It’s an aural illusion. | KOLOstock/Photodisc/Getty Images

If you hold up a seashell to your ear and listen, you may hear what sounds like rolling waves and wind. But it’s not actually the ocean.

Now that we’ve got that out of the way, what exactly is it that you're hearing? In a word, noise—the ambient noise that’s being produced all around and inside you, which you normally don’t hear or pay attention to because it’s too quiet.

To amplify this noise so you can hear it clearly, you need a resonator. Want to make one right now? Form an o shape with your mouth and flick your finger against your throat or cheek. You should hear a note. Make a smaller or larger o, or change the shape of your mouth, and you’ll get different notes (sort of like this). You’re basically letting your mouth fulfill its potential as a Helmholtz resonator, where sound is produced by air vibrating in a cavity with one opening. Different pitches can be coaxed out by changing the shape of the resonating cavity.

The interior of a seashell has many hard, curved surfaces great for reflecting sound and essentially doing the same thing you just did with your mouth. The air moving past and within the shell, the blood flowing through your head, and the conversation going on in the next room create ambient noise, which resonates inside the cavity of the shell, is amplified, and becomes clear enough for us to notice. Just like the various shapes we make with our mouths will produce higher or lower pitches, the sizes and shapes of shells have distinct sounds because different resonant chambers will amplify different frequencies.

The fact that all shells sound just a little bit like the ocean is purely coincidental. Holding any sort of Helmholtz resonator to your ear will produce a similar effect, whether that object is associated with the ocean or not. Put an empty glass over your ear or even cup your hand over it, and the sound you hear will be just about the same.

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A version of this story was published in 2009; it has been updated for 2025.

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