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
31
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.
Active noise-cancellation systems require______.
选项
A、microphones
B、microprocessors
C、loudspeakers
D、all of the above
答案
D
解析
本题的四个选项中,只有D项为正确答案。这可从文中的“…in which microphones,microprocessor,and loudspeaker are all in a unit…”推知。
转载请注明原文地址:https://kaotiyun.com/show/IRhO777K
0
考博英语
相关试题推荐
Atthefall2001SocialScienceHistoryAssociationconventioninChicago,theCrimeandJusticenetworksponsoredaforumonth
Whilestillcatching-uptomeninsomespheresofmodernlife,womenappeartobewayaheadinatleastoneundesirablecategory.
Customerexperienceistheinternalandsubjectiveresponsecustomershavetoanydirectorindirectcontactwithacompany.【B6】
Honestynolongerseemstobethebestpolicywithtellingofliesbecomingacommonpartofourdailylives.Anewresearchby
Acompleteinvestigationintothecausesoftheaccidentshouldleadtoimprovedstandardsandshould_______newoperatingproce
Beingagoodparentishardernowthanithaseverbeenbefore.Inpressurizedmodernlives,demandstobeafulfilledindividua
OnecountrythatiscertainoftheeffectoffilmsontourismisAustralia.TheTouristOfficeofQueenslandsaythatCrocodile
Amongthelowestofthejudicialranks,justicesofthepeaceneverthelessfrequentlyexercisejurisdictionoveravarietyofmi
Thereareavarietyofwaystothinkabouttheself.Twoofthemostwidelyusedtermsareself-conceptandself-esteem.Self-co
However,attimesthisbalanceinnatureis______,resultinginanumberofpossiblyunforeseeneffects.
随机试题
组织的核心过程包括设计程和_____。
工具摆放要()。
在《社会组织与经济组织理论》一书中,他最早提出一套比较完整的行政组织体系理论,因此被称之为“组织理论之父”。他就是德国古典管理理论的代表——韦伯。()
细菌性阴道病正确的是
()是一种较为直观的、通过分析基金在不同市场环境下现金比例的变化情况来评价基金经理择时能力的一种方法。
社会工作者刘洋服务的社区中,有位前年毕业的大学生刘莉莉,她自毕业后一直赋闲在家,无所事事。刘洋想通过帮助刘莉莉上就业指导班或者找工作来改变她无所事事的生活。在未经刘莉莉同意的情况下,刘洋开始了介入行动,最后发现刘莉莉并不愿意这么做。社会工作者刘洋的做法违背
教师在对幼儿的学习与发展进行评价时应注意哪些方面?
影响幼儿心理健康的因素有()
除了大型商场,小丽从不去其他地方购物。所有有钱人都喜欢去大商场购物。大型商场的特点是服务态度好,产品种类多,质量有保证。大部分去大商场购物的人都会在购物后选择在餐厅就餐。如果上述断定为真,则以下哪项一定为真?()
中国共产党在长征途中召开的遵义会议,集中解决了在当时具有决定意义的
最新回复
(
0
)