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.

特别对于噪音性听力丧失而言，耳朵中被损坏的主要区域不是耳膜，也不是你所能看到的耳朵部位，或者中耳内的软骨，事实上是在耳朵内更深的地方。被损坏的区域是些连接大脑的神经，当然，也包括一些特殊的神经元，声音信号通过它们进入大脑。我们正在寻找这些内部的毛状神经元，特别是外部的神经元。当它们长期的使用过度或者刺激过高，它们就会被新陈代谢耗尽。它们工作过度了。它们会临时性的丧失功能，所以你为了听清楚就不得不扩大音量。这些神经元经过一次照射治疗后会恢复功能，但是如果你依然像以前一样让它们操劳过度，它们最终会死掉，并且你的内耳将会失去那些听力功能，这些神经元一旦死掉是无法替代的。

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.

根据经验积累，加上从研究得来的数据显示，当人们每天用那些标准耳塞听音乐90分钟，音量控制在80%以下，能有效的预防和减少患噪音性听力丧失的风险。但是如果你调的音量越大，那么持续听的时间应该尽可能缩短。如果在最大音量的水平，那么你每天最多只能听5分钟。

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.

我不是特别指iPods。无论哪一种随身听都有对人造成听力丧失的潜在危险。我们已经对MP3播放器进行过研究，并且对于其制造商，我们取得了非常相似的成果。一些内置的耳塞能提供比外挂耳塞更高的音量。这也就是说，我们的行为研究报告显示，该类型的耳机与人们设置的不同音量水平几乎无关。这些设置都取决于他们收听环境中的背景噪音水平。当我们把人们放在不同的收听环境中，比如在一架飞行的飞机上——我们利用的噪音是经记录过的波音757飞机，我们在实验室内模仿这样的环境，结果80%的人们最终都设置了那些可能会危害到听力的音量。在波士顿的铁路系统中，其环境噪音水平与飞行中的飞机不相上下，虽然它们听起来不大一样。这些噪音音量非常高，以至于人们在利用耳塞听音乐时设置了过高的音量。

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.

我承认我喜欢那种嘈杂的音乐。我非常喜欢在体育馆内使用iPod。我想它是一项非常伟大的发明。我甚至鼓励人们随心所欲地，想听多大声就听多大声。但是为了以你喜欢的音量听音乐，你必须注意到你听了多长时间。我还要强烈推荐人们去购买好一点的耳塞，这样可以屏蔽背景噪音。经过我们研究，发现有的耳塞能完全密封住耳槽。相比那些主动地消除噪音，将噪音排除在外的耳机，这些都是被动的隔音耳机。目前我要说的就是，二者都能让人们调到自己喜欢的音量——而当人们使用内置耳机时，声音强度最好调得更低一点。