Why Can We Hear the Sound of the Ocean in a Shell? 貝殼傳來海洋之音？

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?

大多數的孩子對從握在耳畔的貝殼里能聽到神奇的海浪澎湃聲嘖嘖稱奇。許多人深信，誰能幸運地撿到大海螺貝殼，便能受邀聆聽大自然最盛大的“原音重現”。

把一個空杯子或只是將手合成杯狀貼近耳朵，就可以聽到類似但比較小的聲音效果。一個比較普遍的解釋認為這是血液在耳朵血管里流動的聲音在杯中回蕩不已引起的效果。這說法是不可能的。因為照這樣的解釋，人在劇烈運動后聽到的聲音應該會更大，但事實上仍然維持相同的音量。

在貝殼或杯子里流動的空氣，也被認為是產生聲音的可能因素之一，然而在隔音的房間里所做的實驗已將這個可能推翻。雖然隔音房內有充足的空氣，貝殼里卻一片安靜。事實上，問題的答案非常簡單，簡單到可以用兩個字來概括：周圍的雜音。

我們處在不斷的雜音包圍之中，其中大部分雜音我們是聽不見的，除非把貝殼之類的東西靠近耳邊才能聽到。從周圍大范圍空氣中收集來的聲波會在貝殼里面產生共鳴，這樣我們就能聽到更多環繞在我們四周的雜音，不過聽起來雜亂不堪。

貝殼中的聲音會隨著周圍雜音的音量變大而增強。因此“海洋”的聲音在一個嘈雜的房間中聽來會更大。因為房間里多重復雜的聲音會在貝殼中來回激蕩、相互混雜。我們聽到聲音的大小同時也取決于貝殼與耳朵的角度及距離。

過去，海螺貝殼螺旋狀的尖端常被用作聽障人士的助聽器。如今，貝殼成了許多客廳櫥柜的裝飾品。如果你有一個大貝殼，何不閉上眼睛，讓自己去海邊度個小假呢？