Particularly with noise-induced hearing loss, the primary area where the ear is damaged is not the eardrum, not the part of the ear that you can see and not the bones that are inside the middle ear — it is actually deeper inside. It's where the nerve that brings the sound message up to the brain connects with the inner ear, and it involves some very specialized cells. These are hair cells, and specifically we're looking at the outer hair cells. When they're overexposed or stimulated at too high a level for too long a duration, they end up being metabolically exhausted. They are overworked. They temporarily lose their function, so sound has to be made louder in order for you to hear it. These cells can recover after a single exposure, but if you overexpose them often enough, they end up dying, and you lose that functional ability inside your inner ear. The cells that die are not replaceable.

特別對于噪音性聽力喪失而言，耳朵中被損壞的主要區域不是耳膜，也不是你所能看到的耳朵部位，或者中耳內的軟骨，事實上是在耳朵內更深的地方。被損壞的區域是些連接大腦的神經，當然，也包括一些特殊的神經元，聲音信號通過它們進入大腦。我們正在尋找這些內部的毛狀神經元，特別是外部的神經元。當它們長期的使用過度或者刺激過高，它們就會被新陳代謝耗盡。它們工作過度了。它們會臨時性的喪失功能，所以你為了聽清楚就不得不擴大音量。這些神經元經過一次照射治療后會恢復功能，但是如果你依然像以前一樣讓它們操勞過度，它們最終會死掉，并且你的內耳將會失去那些聽力功能，這些神經元一旦死掉是無法替代的。

As far as a rule of thumb goes, the figures we got in our studies were that people using that standard earbud could listen at about 80% of maximum volume for 90 minutes per day or less without increasing their risk for noise-induced hearing loss. But the louder the volume, the shorter your duration should be. At maximum volume, you should listen for only about 5 minutes a day.

根據經驗積累，加上從研究得來的數據顯示，當人們每天用那些標準耳塞聽音樂90分鐘，音量控制在80%以下，能有效的預防和減少患噪音性聽力喪失的風險。但是如果你調的音量越大，那么持續聽的時間應該盡可能縮短。如果在最大音量的水平，那么你每天最多只能聽5分鐘。

I don't want to single out iPods. Any personal listening device out there has the potential to be used in a way that will cause hearing loss. We've conducted studies of a few MP3 players and found very similar results across the MP3 manufacturers. Some in-the-ear earphones are capable of providing higher sound levels than some over-the-ear earphones. That said, studies we've done on behavior show that the type of earphones has almost nothing to do with the level at which people set their headphones. It's all dictated by the level of background noise in their listening environment. When we put people in different listening environments, like flying in an airplane — we used noise we'd recorded while flying on a Boeing 757 commercial flight, and we simulated that environment in our lab — 80% of people listened at levels that would eventually put their hearing at risk. On the subway system here in Boston, the ambient noise levels are very comparable to the level on an airplane, although it sounds very different. The noise is sufficiently high that it induces people to listen to their headphones at excessively loud volume.

我不是特別指iPods。無論哪一種隨身聽都有對人造成聽力喪失的潛在危險。我們已經對MP3播放器進行過研究，并且對于其制造商，我們取得了非常相似的成果。一些內置的耳塞能提供比外掛耳塞更高的音量。這也就是說，我們的行為研究報告顯示，該類型的耳機與人們設置的不同音量水平幾乎無關。這些設置都取決于他們收聽環境中的背景噪音水平。當我們把人們放在不同的收聽環境中，比如在一架飛行的飛機上——我們利用的噪音是經記錄過的波音757飛機，我們在實驗室內模仿這樣的環境，結果80%的人們最終都設置了那些可能會危害到聽力的音量。在波士頓的鐵路系統中，其環境噪音水平與飛行中的飛機不相上下，雖然它們聽起來不大一樣。這些噪音音量非常高，以至于人們在利用耳塞聽音樂時設置了過高的音量。

I'm a self-professed loud-music listener. I use my iPod at the gym, and I love it. I think it's one of the greatest inventions ever. I even advocate that people listen to music as loud as they want. But in order to listen as loud as you want, you need to be careful about how long you're listening. I would also strongly recommend that people invest in better earphones that block out background noise. Some of the research we did studied earphones that completely seal up the ear canal. These are passive sound-isolating earphones, as opposed to the ones that are active noise cancelers that block out some of the noise. As far as I can tell, both would allow people to listen to their headphones at their chosen level — and more likely at a lower volume than if they were using the stock earbuds.

我承認我喜歡那種嘈雜的音樂。我非常喜歡在體育館內使用iPod。我想它是一項非常偉大的發明。我甚至鼓勵人們隨心所欲地，想聽多大聲就聽多大聲。但是為了以你喜歡的音量聽音樂，你必須注意到你聽了多長時間。我還要強烈推薦人們去購買好一點的耳塞，這樣可以屏蔽背景噪音。經過我們研究，發現有的耳塞能完全密封住耳槽。相比那些主動地消除噪音，將噪音排除在外的耳機，這些都是被動的隔音耳機。目前我要說的就是，二者都能讓人們調到自己喜歡的音量——而當人們使用內置耳機時，聲音強度最好調得更低一點。