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现代科技研究表明，歌声在未来或许不仅可用来欣赏和娱乐，还可以用来灭火！

For over 150 years, scientists have known that fires can be extinguished1) with sound waves, but they still don't know how.

"I throw more power into my voice, and now the flame is extinguished," wrote Irish scientist John Tyndall about his experiments with sound and fire in 1857. After countless public demonstrations and a handful of lab tests, researchers are still struggling to determine exactly how sound snuffs2) flames.

Sound travels in waves, which are simply variations of pressure in a medium—whether solid, liquid or gas. The energy from vibrating3) objects moves from particle to particle in the air in a repeating pattern of high- and low-pressure zones that we perceive as sound. According to the ideal gas law, temperature, pressure and volume4) are related; therefore, a decrease in pressure can lead to a corresponding decrease in temperature, which may explain how sound can extinguish a flame.

In 2004, Dmitry Plaks, now a student at the Georgia Institute of Technology, and his classmates at the University of West Georgia tested whether sound waves could extinguish fires in hopes of using sound to extinguish flames in a spacecraft. They placed a candle in a large topless chamber with three bass5) speakers attached to the walls. The candle was lit and the Canadian rock band Nickelback6)'s "How You Remind Me" was pumped through the speakers. Within roughly 10 seconds, once the song hit a low note, the flame was out.

Physicist James Espinosa, a former advisor to the student team, notes that the candle wasn't running out of oxygen to fuel the flame because the chamber was large and open to the air. He also doesn't believe that wind—which would actually displace the warm air around the candle with cooler air—had put out the fire. There is another indication that the fire hadn't been extinguished by wind: frequency7). The students tested a range of frequencies and found that the effective range was between 40 and 50 hertz, within the range of human hearing.

Plaks speculates8) that the pressure drop created by the sound wave was what extinguished the flame. Gary Ruff, project manager for fire suppression technologies at NASA's Glenn Research Center, agrees: if the difference between the high-pressure peak and low-pressure trough9) in the sound wave was large enough, the flame would go out.

Such acoustic10) fire suppression might prove useful in space, Espinosa suggests. But Ruff and NASA disagree with him: Making the sound waves to extinguish a fire would require electricity, and astronauts would also have to be able to see the flames in order to direct sound waves at them.

Nevertheless, this summer Espinosa will try to extinguish a larger flame with a smaller speaker system. He plans to create an electric arc11), like that used for welding12). This spark creates a shock wave13) that can be focused with an acoustic horn14) so that an array15) of such waves can be aimed at the fire.

Such a system might prove useful here for putting out fires in locations whose contents could be damaged by water, such as museums that house valuable artwork or centers with data servers or other electrical equipment. "Sound is being used to cut pieces of metal, to destroy kidney stones," Espinosa adds. "It can do more than people give it credit for16)," including, apparently, firefighting.

一百五十多年以来，科学家们早已知道可以用声波来灭火，但他们还是没找出灭火的方法。

“我提高了嗓音，接着火焰被熄灭了。”这是1857年爱尔兰科学家约翰·廷德耳写下的一段实验记录，实验研究的是声音与火的关系。经过无数次公开演示及一系列实验测试，研究人员仍在努力探究声音能灭火的确切原因。

声音以波的形式传播，声波其实就是介质中的压力变化——不管介质是固态、液态还是气态。振动的物体发出的能量在空气中的粒子间传递，形成一系列连续的高压带和低压带——这就产生了我们听到的声音。根据理想气体定律，温度、压力和体积三者相关；因此，气压的降低可以引起温度的相应降低，这或许可以解释声音为什么能灭火。

德米特里·普拉克斯现在是佐治亚理工学院的学生。早在2004年，他和西佐治亚大学的同学就曾做过一个实验，研究声波能否灭火，以期能用声音来扑灭航天飞机内的火焰。他们把一支蜡烛放入一个无盖的大燃烧室，并在燃烧室的内壁上安装了三个低音喇叭。蜡烛点燃后，那些超低音喇叭就开始播放加拿大摇滚乐队“五分钱乐队”的歌曲《你如何提醒我》。结果，大概在10秒内，歌曲只要唱到一个低音处，蜡烛就会熄灭。

物理学家詹姆斯·埃斯皮诺萨曾担任过这个学生实验组的指导老师。他指出，蜡烛并不是因燃烧所需的氧气耗尽而熄灭的，因为实验所用的燃烧室很大，而且不是密闭的。他还认为，也不是风使火熄灭的——虽然风确实能让冷空气取代蜡烛周围的热空气。另有迹象表明，火并不是被风吹灭的，那就是频率。学生们当时对不同波段的频率进行了测试，发现对灭火有效的频率介于40～50赫兹之间，而这一波段在人类的听觉范围之内。

普拉克斯推断，声波引起的气压下降是让火焰熄灭的原因。加里·拉夫是美国宇航局(下称NASA)格伦研究中心的灭火技术项目负责人，他赞同普拉克斯的观点：如果声波中高压的波峰与低压的波谷之间的压力差足够大的话，火就会被熄灭。

埃斯皮诺萨认为，这种声学灭火法或许能在太空派上用场。不过拉夫和NASA并不认同他的看法：产生灭火用的声波需要用电，而且航天员还必须看得到火焰，才能将声波瞄准火焰。

不过，今年夏天，埃斯皮诺萨将尝试使用更小的扬声装置来扑灭更大的火势。他打算制造出类似焊接所用的电弧。电弧光会产生冲击波，而这种冲击波可以通过射声器聚焦后对准火焰传送。

这种灭火系统也许最终会对摆放有怕水物体的场所的灭火工作十分有用，比如在收藏有珍贵艺术品的博物馆和装有数据服务器或其他电子设备的中心场所。“声波已被用来切割金属和粉碎肾结石，”埃斯皮诺萨补充说，“它的用途远比人们认为的要多，”显然也包括灭火。

Vocabulary

1. extinguish [Ik5stIN^wIF] vt. 熄灭，扑灭(火等)

2. snuff [snQf] vt. 熄灭，掐灭(蜡烛等)

3. vibrate [vaI5breIt] vi. 颤动；振动；抖动

4. volume [5vRlju:m; (?@) -jEm] n. 音量，声量；响度

5. bass [beIs] adj. (乐器)低音的

6. Nickelback: 加拿大当红摇滚乐队，其专辑All the Right Reasons自2005年发行以来，创下了在美国音乐排行榜Billboard 200中停留156周的纪录，迄今为止总销量接近700万张。最新专辑Dark Horse也凭借32.6万张的骄人销量夺得了Billboard 2008年12月的亚军。

7. frequency [5fri:kwEnsI] n. 【物】频率，周率

8. speculate [5spekjuleIt] vt. 推测，推断

9. trough [trC:f] n. 【物】波谷

10. acoustic [E5ku:stIk] adj. 受声波控制的

11. electric arc: 电弧；arc [B:k] n. 弧

12. welding [5weldIN] n. 焊接；焊合

13. shock wave: 冲击波，运动气体中的强压缩波

14. acoustic horn: 射声器，喇叭(筒)，传话筒

15. array [E5reI] n. 整齐的一批；大量

16. give sb./sth. credit for: 认为某人(物)有(某种优点或能力)