why do we hear the ocean in a shell
comments Share Print Why do you 'hear the ocean' in a seashell? We live in a sea of sound but can we capture the essence of the ocean in a seashell? Dr Karl visits the seaside to see what he can hear. By It's a lovely experience to walk on the beach, and it can be made even lovelier by finding a large empty seashell and putting it to your ear, and hearing the sounds of the ocean. It also gives grown-ups a feeling of benevolent omnipotence to pass the shell to kids, and to see the amazement on their faces. The ocean can't possibly be inside the shell, so the sounds of the ocean coming from the pink walls of a seashell seem like magic. So what are you actually hearing in the shell? The answer is that you are hearing the local noises already around you, but altered by the shell thanks to some clever physics. One popular (but wrong) explanation is that you are listening to your own blood coursing through you. This explanation might be based on the fact that you can sometimes hear the pulsing of blood as you lay your head onto a soft pillow. It's easy to disprove this theory with a simple experiment. 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. You'll find that the loudness of the 'sound of the sea' is still the same. So now for a three-part explanation. The first part of the explanation is that the shell acts like a 'resonator'. When you blow air strongly through your pursed lips over the mouth of an empty bottle, you will hear a musical note.
The sound is resonating in the bottle. You and I might call it a "bottle" but a physical acoustician would call it a "resonant cavity". Getting back to our seashell, the inside is hard with an almost-glazed finish so it's an excellent reflector of sound (it's a resonator). It also has quite an irregular shape so it will resonate at many frequencies. In the same way, this acoustic filter (or shell-near-the-ear) dampens one frequency (or pitch), and boosts other frequencies. In one study, in a typical noisy room, a cup was held to the ear and a tiny microphone held right next to the eardrum. (They chose a cup, because it has a 'simpler' shape than the internal complexities of a seashell. ) The microphone registered 15 decibels louder at the cup's resonant frequency of 648 hertz (as compared to not having the cup there at all). But at double the frequency (1296 hertz), the sound heard was 16 decibels quieter. But to give you the ocean sound, the shell definitely needs the ambient or background sound. No ambient sound, no 'ocean-in-the-shell' sound. If you go into a soundproof room, and listen to your favourite seashell, you'll hear nothing. The second part of the explanation is that our human brain is superb at finding subtle patterns in the chaotic world around us. We can find animals in clouds, or the face of Jesus in a potato chip, or the Virgin Mary in a fencepost. The third part of the explanation is that we live in a sea of sound, but we mostly ignore it. This is similar to the phenomenon of being able to feel our socks and underwear for a few brief moments after we put them on.
Our brain then blocks the socks/underwear from our consciousness for the rest of the day. In the same way, our brain usually blocks most of the noise of the background buzz. So now we can put it all together. The shell close to your ear acts like the audio equivalent of yellow-tinted sunglasses. It changes the make-up of the sounds that continually assault our ears, and that we continually ignore. For example, it lets through more of one frequency, but less of another frequency. So the combination of 'ear and brain' recognises that something has changed in the incoming noise. The brain tries to put a label on this new noise, and notices that you are near the ocean so it labels this noise as "ocean". But some people find different patterns in seashell noise. There's a strange psychic phenomenon called 'shell scrying'. It encourages you to listen carefully to the shell. First, they say, you should hear fragments of words, then words, and finally, whole segments of conversation. Tags:, 2018 Karl S. Kruszelnicki Pty Ltd Kevin in Bentonville, Arkansas, wrote in to ask this question: "Why do you hear the ocean when you put a seashell up to your ear? "M All right, first things first: no matter how much it may sound like the rolling waves, it's not actually the ocean you're hearing in a shell. 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 on the cheap? 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. What you're doing here is 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 seashell you're listening tothe inside of which has many hard, curved surfaces great for reflecting soundis essentially doing the same thing you just did with your mouth. The ambient noise mentioned beforethe air moving past and within the shell, the blood flowing through your head, the conversation going on in the next roomis resonating inside the cavity of the shell, being amplified and becoming clear enough for us to notice. Just like the various shapes we make with our mouths will produce different pitches, different sizes and shapes of shell sound different 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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