首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, b
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, b
admin
2013-11-29
19
问题
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, blaring car alarms, and roving boom boxes come first, second, and third on my list of most obnoxious noise offenders, but everyone could come up with his own version of aural hell—if he could just find a quiet spot to ponder the matter.
Yet what technology has done, other technology is now starting to undo, using computer power, to zap those ear-splitting noises into silence. Previously silence-seekers had little recourse except to stay inside, close the windows, and plug their ears. Remedies like these are quaintly termed "passive" systems, because they place physical barriers against the unwanted sound. Now computer technology is producing a far more effective "active" system, which doesn’t just contain, deflect, or mask the noise, but annihilates it electronically.
The system works by countering the offending noise with "anti-noise", a somewhat sinister-sounding term that calls to mind antimatter, black holes, and other Popular Science mindbenders but that actually refers to something quite simple. Just as a wave on a pond is flattened when it merges with a trough that is its exact opposite (or mirror image) , so can a sound wave be negated by meeting its opposite.
This general theory of sound cancellation has been around since the 1930s. In the fifties and sixties it made for a kind of magic trick among laboratory acousticians playing around with the first clunky mainframe computers. The advent of low-cost high-power microprocessors has made active noise-cancellation systems a commercial possibility, and a handful of small electronics firms in the United States and abroad are bringing the first ones onto the silence market.
Silence buffs might be hoping that the noise-canceling apparatus will take the shape of the 44 Magnum wielded by Dirty Harry, but in fact active sound control is not quite that active. The system might more properly be described as reactive, in that it responds to sound waves already headed toward human ears. In the configuration that is usual for such systems microphones detect the noise signal and send it to the system’s microprocessor, which almost instantly models it and creates its inverse for loudspeakers to fire at the original. Because the two sounds occupy the same range of frequencies and tones, the inverse sounds exactly like the noise it is to eliminate: the anti-noise cancelling Beethoven’s Fifth Symphony is heard as Beethoven’s Fifth. The only difference is that every positive pressure produced on the air by the orchestra is matched by a negative pressure produced by the computer, and every negative pressure is matched by a positive, thereby silencing the sound. The system is most effective as a kind of muffler, in which microphones, microprocessor, and loudspeaker are all in a unit encasing the device that produces the sound, stifling it at its source. But it can work as a headset, too, negating the sound at the last moment before it disturbs one’s peace of mind.
According to the passage, an active noise-cancellation system______.
选项
A、contains noise rather than negates it
B、eliminates noise rather than muffles it
C、deflects noise rather than baffles it
D、holds noise back rather than stifles it
答案
B
解析
本题的四个选项中,只有B项为正确答案。这可从文中第二段的最后一句“…which doesn’t just contain,deflect,or mask the noise,but annihilates it electronically”推知。
转载请注明原文地址:https://kaotiyun.com/show/nRhO777K
0
考博英语
相关试题推荐
Inrecentyears,railroadshavebeencombiningwitheachother,mergingintosupersystems,causingheightenedconcernsaboutmo
Inrecentyears,railroadshavebeencombiningwitheachother,mergingintosupersystems,causingheightenedconcernsaboutmo
BetweentheinventionofagricultureandthecommercialrevolutionthatmarkedtheendoftheMiddleAges,wealthandtechnology
Justiceinsocietymustincludebothafairtrialtotheaccusedandtheselectionofanappropriatepunishmentforthoseproven
MorethanhalfofallJewsmarriedinU.S.since1990havewedpeoplewhoaren’tJewish.Nearly480,000Americanchildrentrader
Acompleteinvestigationintothecausesoftheaccidentshouldleadtoimprovedstandardsandshould_______newoperatingproce
Everycultureattemptstocreatea"universeofdiscourse"foritsmembers,awayinwhichpeoplecaninterprettheirexperience
OnecountrythatiscertainoftheeffectoffilmsontourismisAustralia.TheTouristOfficeofQueenslandsaythatCrocodile
Ourpresentgenerationofculturalcritics,arrivingaftertheassaultofpostmodernismandtheincreasinglywidespreadcommerci
Duringourlivesallofusareexposedtothepossibilityofavarietyofriskeventssuchas:workaccidents,majorillness,de
随机试题
[*]用凑微分及分部积分法求之.解
Shetriesherbestto___________thechangesinfashion.
有关骨关节结核,下列哪项错误
横曲线由哪些牙尖的连线所构成
引进设备合同中设备权利担保是指卖方对提供设备的()担保。
在各种开挖方法中,初期支护无需拆除的方法是()n
用于向上级汇报工作进程,反映工作问题,总结工作经验教训的是()。
院的外科病区有甲、乙、丙、丁、戊等5位护士,她们负责病区1、2、3、4、5,、6、7号等7间病房的日常护理工作,每间病房只由一位护士来护理,每位护士至少护理一间病房,在多年的护理过程中,她们已经形成特定的护理习惯和经验。已知:(1)甲护理1、2号两间病房
一个社会的文明水平,一个人的文明水平,在相当程度上取决于职业道德意识的强弱和深浅。()
Unlesswespendmoneytospotandpreventasteroids(小行星)now,onemightcrashintoEarthanddestroylifeasweknowit,sayso
最新回复
(
0
)