Why Can We Hear the Sound of the Ocean in a Shell? 贝壳传来海洋之音？

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?

大多数的孩子对从握在耳畔的贝壳里能听到神奇的海浪澎湃声啧啧称奇。许多人深信，谁能幸运地捡到大海螺贝壳，便能受邀聆听大自然最盛大的“原音重现”。

把一个空杯子或只是将手合成杯状贴近耳朵，就可以听到类似但比较小的声音效果。一个比较普遍的解释认为这是血液在耳朵血管里流动的声音在杯中回荡不已引起的效果。这说法是不可能的。因为照这样的解释，人在剧烈运动后听到的声音应该会更大，但事实上仍然维持相同的音量。

在贝壳或杯子里流动的空气，也被认为是产生声音的可能因素之一，然而在隔音的房间里所做的实验已将这个可能推翻。虽然隔音房内有充足的空气，贝壳里却一片安静。事实上，问题的答案非常简单，简单到可以用两个字来概括：周围的杂音。

我们处在不断的杂音包围之中，其中大部分杂音我们是听不见的，除非把贝壳之类的东西靠近耳边才能听到。从周围大范围空气中收集来的声波会在贝壳里面产生共鸣，这样我们就能听到更多环绕在我们四周的杂音，不过听起来杂乱不堪。

贝壳中的声音会随着周围杂音的音量变大而增强。因此“海洋”的声音在一个嘈杂的房间中听来会更大。因为房间里多重复杂的声音会在贝壳中来回激荡、相互混杂。我们听到声音的大小同时也取决于贝壳与耳朵的角度及距离。

过去，海螺贝壳螺旋状的尖端常被用作听障人士的助听器。如今，贝壳成了许多客厅橱柜的装饰品。如果你有一个大贝壳，何不闭上眼睛，让自己去海边度个小假呢？