英语听力文摘 English Digest 285、手枪消音器

　　Gun Silencers
所谓“消声手枪”也不可能是完全无声，只是将声音尽量降低。手枪的消声方法有很多. 手枪的声音主要来自子弹出膛，空气冲出枪口是巨大的压力对外面的空气引起的冲击震动.消声器是安装在空气动力设备(如鼓风机、空压机)的气流通道上或进、排气系统中的降 低噪声的装置。消声器能够阻挡声波的传播，允许气流通过，是控制噪声的有效工具。消声器的种类很多，但究其消声机理，又可以把它们分为六种主要的类型，即阻性消声器、抗性消声器、阻抗复合式消声器、微孔板消声器、小孔消声器和有源消声器.阻性消声器主要是利用多孔吸声材料来降低噪声的。把吸声材料固定在气流通道的内壁上或按照一定方式在管道中排列，就构成了阻性消声器。当声波进入阻性消声器时,一部分声能在多孔材料的孔隙中摩擦而转化成热能耗散掉，使通过消声器的声波减弱 。阻性消声器就画像电学上的纯电阻电路，吸声材料类似于电阻。因此，人们就把这种消声器称为阻性消声器。阻性消声器对中高频消声效果奸、对低频消声效果较差。

　　You’ve seen them in spy movies. The evil assassin is about to kill the helpless victim, but he’s worried that someone might hear the shot. What’s an evil assassin to do? In Hollywood, the answer is simple: He deftly¹ attaches a silencer to his gun, fires a soundless shot, then escapes into the night. Do silencers really work this way?
Actually, real silencers are likely to be bulkier and noisier than the ones in a Hollywood stockroom. Many are actually larger than the guns they are designed to work with, and no silencer can remove ALL sound of a shot.
Most of a gunshot’s noise comes from hot gasses bursting out of the gun behind the bullet. The more suddenly these gasses emerge, the sharper and louder the sound will be. A silencer works by slowing and cooling this burst of gas, trapping it in a spiral of steel wool and forcing it to exit the gun more gradually. As they emerge, these slower moving gasses make less sound than the concentrated burst of a normal gunshot.
You can feel the difference yourself by making the sounds”Bam!” and “Phoof!” The sharp burst of air following the “B” sound of “Bam!” will make a sharper, more percussive² noise than the more gradual escape of “Phoof!” It’s the same difference as letting the air out of a balloon slowly instead of popping it. Both gun silencers and car mufflers work the same way—they were invented by the same person, Hiram Maxim³, in the early twentieth century. Maxim didn’t care much about gun-toting(带枪的) assassins or spy movie screenwriters. He was ecologically minded. What was his main, ecological⁴ concern? Noise pollution!

1 deftly   

adv.灵巧地，熟练地，敏捷地

参考例句：

• He deftly folded the typed sheets and replaced them in the envelope. 他灵巧地将打有字的纸折好重新放回信封。 来自《简明英汉词典》
• At last he had a clew to her interest, and followed it deftly. 这一下终于让他发现了她的兴趣所在，于是他熟练地继续谈这个话题。 来自英汉文学 - 嘉莉妹妹

2 percussive   

adj.敲击的

参考例句：

• When it is dragged over pliant areas, an additional percussive tap could indicate this collision. 当它被拖到受范区域时，一个附加的敲击声提示这种碰触。 来自About Face 3交互设计精髓
• Pneumatic DTH (Down-The-Hole) hammer is one of main pneumatic percussive-rotary drilling equipments. 风动冲击器是气动冲击回转钻进的主要设备之一。 来自互联网

3 maxim   

n.格言，箴言

参考例句：

• Please lay the maxim to your heart.请把此格言记在心里。
• "Waste not,want not" is her favourite maxim.“不浪费则不匮乏”是她喜爱的格言。

4 ecological   

adj.生态的，生态学的

参考例句：

• The region has been declared an ecological disaster zone.这个地区已经宣布为生态灾难区。
• Each animal has its ecological niche.每种动物都有自己的生态位.