Why can you hear the sea when you put a shell to your ear? Many of us have picked up a seashell, held it against an ear and heard the sound of the sea. But where does this sound, that is so reminiscent of waves splashing on the shore, actually come from?
The answer is that the sound you hear when pressing a shell against your ear comes from the surrounding environment. Wherever you are in the world, there is always some ambient noise present, however quiet it may be. When you put a shell to your ear it acts as a resonant chamber, amplifying some of the frequencies present in this background noise. These accentuated frequencies combine to give the characteristic shhhhh sound that reminds us of waves breaking on a beach. The exact nature of the sound depends on the shape and size of the shell. The larger the shell, the lower the frequencies that are emphasised and the deeper in tone the sound that is heard.
The following two audio tracks demonstrate this effect. Each recording was made by positioning a microphone at the entrance to a large seashell. The same recording levels were used in both cases.
Surf or turf?
This first audio track was recorded in a courtyard located outside a group of offices. The background noise level was as you might expect on a normal day. If you play track one, you should be able to hear the characteristic shhhhh sound associated with putting a seashell against your ear. If you listen carefully, you may also be able to hear some birdsong in the background.
Sounds of silence
The second audio track was recorded in an anechoic chamber – a room whose walls, floor and ceiling are lined with foam wedges. This provides a high level of soundproofing, ensuring that the ambient noise within the anechoic chamber is minimal. If you play track two, you should be able to hear that the characteristic shhhhh sound is now barely audible.
The real thing
You can compare the sound from a seashell with the real sound of the sea by listening to this final audio track. It was recorded on a beach and features the soothing sound of waves lapping on to the shore.