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Unwanted sound， or noise， such as that produced by airplanes， traffic， or industrial machinery， is considered a form of pollution.Noise pollution is at its worst in densely populated areas.It can cause hearing loss， stress， high blood pressure，sleep loss，distraction，and lost productivity.
Sounds are produced by objects that vibrate1 at a rate that the ear can detect2. This rate is called frequency and is measured in hertz3， or vibrations per second. Most humans can hear sounds between 20 and 20，000 hertz， while dogs can hear high-pitched4 sounds up to 50，000 hertz. While high-frequency sounds tend to be more hazardous5 and more annoying to hearing than low-frequency sounds， most noise pollution damage is related to the intensity of the sound. Measured in decibels6， noise intensity can range from zero， the quietest sound the human ear can detect， to over 160 decibels. Conversation takes place at around 40 decibels， a subway train is about 80 decibels， and a rock concert is from 80 to 100 decibels. The intensity of a nearby jet taking off is about 110 decibels. The threshold for pain， tissue damage， and potential hearing loss in humans is 120 decibels. Long-lasting， high-intensity sounds are the most damaging to hearing and produce the most stress in humans.
Solutions to noise pollution include adding insulation7 and sound-proofing8 to doors， walls， and ceilings； using ear protection， particularly in industrial working areas； planting vegetation to absorb and screen out9 noise pollution； and zoning10 urban areas to maintain a separation between residential areas and zones of excessive noise.
噪音，人类的杀手
人们不希望听到的声音，或称噪音，比如飞机、交通车辆或工业机械产生的噪音，被认为是一种污染。在人口密集的地区噪音污染的影响最糟。它可以导致人们失聪、精神紧张、血压升高、睡眠减少、注意力分散以及生产力降低。
物体以人耳能感觉的速率振动而产生声音。这种速率叫做频率，计算单位为赫兹（每秒钟振动频率）。大多数人能够感觉到20至20000赫兹的声音，而犬类能听到高达50000赫兹的高频声音。虽然高频声音比低频声音更加危险且恼人，大多数的噪音污染损害却与声音强度有关。按分贝计算，噪音强度可以从零 （人耳所能感到的最低声音）到160分贝以上。人交谈的声音强度一般为40分贝，地铁的噪音强度约为80分贝，摇滚音乐会声音强度在80到100分贝之间。一架在附近起飞的喷气机的声音强度大约是110分贝。120分贝是人类感到痛苦、组织受损、造成潜在的听力丧失的下限。长期高强度的声音对听力损害最大，给人类带来最紧张的情绪。
解决噪音污染的措施包括对门、墙和天花板进行隔音处理，使用耳朵保护装置（尤其是在工业生产区），种植植物吸收并屏蔽噪音，对城市分区使居住区与过量噪音区分开。
注释：
1.vibrate vi.振动，抖动，振动着传播
2.detect vt.测出，察觉，侦查出
3.hertz n.（物）赫兹（频率的单位，略作Hz）
4.high-pitched adj.声调高的，失声的
5.hazardous adj.有危险的，有危害
6.decibel n.分贝（表声音强度的单位）
7.insulation n.隔音，隔音材料
8.soundproofing n.隔音设备
9.screen vi.屏蔽～out去掉，消除
10.zone vt.将…分成区，指定…为区
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