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2013四川高考状元>福州sat培训
PARTⅠLISTENING COMPREHENSION?
SECTION A TALK?杰克逊吉隆坡演唱会
As we all know,when machines work they give off a lot of noi,and the noi can sometimes be very unpleasant,or annoying.As a result,people have been trying to find ways to reduce noi.Although it may sound a bit strange to you all,one of the best ways to make machines quieter,in cars for example,may be to make them noisier.The source of this paradox is electronic anti-noi which creates sound waves to cancel out unwanted noi,such as rattles,blare,etc.
eliminateNow although the idea dates back to the 1930s,it’s only recently that advances in computer technology have made anti-noi a commercial possibility.Take Franc e for example.Here industry spends a fortune to get rid of noi.We all know how unpleasant it is.Both people working in factories and ordinary people at home enjoying their leisure can be affected by noi.Delicate machines are affected by noi as well.The government has pasd a lot of regulations concerning acceptable levels of noi.?
Noi is costly to industry.In the first place,just following a single regulation can cost 1 to 2 billion US dollars in the textile industry,they say.store是什么意思
only child>环抱Then condly,of cour,vibration can cau damage to machinery.Even very small vibrations can cau parts to wear out and equipment to fail.And naturally enough,this gets added on to the price of the products.About$to 15%of the price of a product comes from noi and vibration costs,it’s estimated.?
At prent,methods ud to dampen down noi and vibrations rely on techniques that are 30 or 40 years old.The usually involve wrapping the noisy or vibrating component in anything from cotton to concrete.But this is often expensive and inefficient.?
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The modern electronic anti-noi devices don’t reduce sound.Instead,sound is ud to attack sound.The trick is to hit the sound waves with other waves in a carefully controlled way.It may not be possible to eliminate noi completely,but engineers can build systems to eliminate specific kinds of noi and vibration.The new systems can deal with repetitive noi.This unfortunately means that there is not much that can be done about one-off noi,like someone try ing to learn to play a trumpet.But they can handle fairly regular things like engine noi.?
A French company has developed a technique which us a microphone and a microprocessor.The processor measures the sound and directs a speaker to broadcast sound waves that are out of pha with the engine noi.The company claimed t hat it will make a car engine quieter,if not completely 100%silent.There are a number of other areas of application in the noisy,industrial environment of today.One system which the company is developing,aims to minimize the noi of aircraft engines and helicopter vibrations.Now anti-noi systems would be able to reduce noi in the cabin of an airplane to mere acceptable levels.?
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Another area which affects ordinary houholds nowadays concerns the noi which electricity and gas suppliers create.The electricity companies spend a lo t of money each year,cutting the harm of transformers,trying to quiet the noi and maintaining equipment that is constantly affected by vibration.If they can get rid of or even stop the vibrations,manufacturers can increa
production speeds.But,of cour,people working in noisy workplaces are perhaps mere affected than anything by the effects of noi.Anti-noi can also create“zones of quiet”in noisy workplaces.To create such a zone,you do two things.
First,microphones are suspended around the workplace.Then speakers that produce out-of-pha sound waves can then be put clo to the worker under the desk o r the machine.A company working in this area has tested this system and says that it cuts noi levels enough for somebody inside the zone to hear a conversation from another part of the work place.Yet,this is only one-way;shouts from t he quiet zone could not be heard over the factory noi by tho outside it,becau the rest of the workplace remains noisy.This is one of the anti-noi measures experimented with today.If this proves to be feasible in many workplaces,I’m sure it can contribute to the reduction of noi in factory workshops in the future.
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