Why Can We Hear the Sound of the Ocean in a Shell?
Most children have probably wondered at the noise of roaring ocean waves magically captured inside seashells held up to their ears. According to popular belief, anyone lucky enough to hold a big, spiral conch shell will be treated to the loudest rendition of one of nature's "recordings."
A similar, but quieter effect can be heard by using an empty cup or even just by cupping a hand over an ear. One popular explanation is that the sound of blood rushing through the ear's blood vessels echoes inside the cup. This is unlikely, because the sound ought to be louder after vigorous exercise, yet it remains at the same level.
Air flowing through the shell or cup has also been suggested as a possible cause, but experiments in soundproof rooms have disproved this. No sound comes from the shell, though there is plenty of air in the room. In fact, the answer is fairly simple, and can be summed up in two words: ambient noise.
We are constantly surrounded by noise, most of which is not audible to us unless we hold something like a seashell close to one of our ears. The sound waves collected from a larger area resonate inside it and we hear a greater amount than usual of the ambient sound around us, though in a jumbled up form.
The noise in the shell increases along with the level of ambient noise in the surrounding area. The "ocean" is a lot louder in a noisy room where a multitude of sounds bounce around and mix together inside the shell. The level of noise we hear also depends on the angle and distance of the shell from the ear.
In the past, the spiral tips of conch shells were often used as aids for the hearing impaired. Nowadays, shells decorate many a living room cabinet. If you have a big seashell, why not close your eyes and treat yourself to a quick trip to the seaside?