【正确答案】 C

【答案解析】[解析] Transcript Interviewer: Now, turning to the problem of noise - what can we do to fight the increasing huge volumes of noise affecting us all today, like the noise you can hear in the background in this factory we're standing in now? I have with me Dr Susan Hall, one of North America's leading experts on what is called 'anti-noise'. Dr Hall, what can be done? Dr Hall: Well, strange though it may sound to you, one of the best ways to make machinery quieter, like in cars, for example, may be to make it noisier. Interviewer: Really? Dr Hall: Yes, the source of this paradox is electronic 'anti- noise', which creates sound waves to combat unwanted rattles, blare and thumping. Now although the idea dates back to the 1930s, it's only recently that advances in computer technology have made 'anti-noise' a commercial possibility. Interviewer: And where has this happened? Dr Hall: Well, America. Interviewer: Huhuh. Dr Hall: Here industry spends a fortune to get rid of noise. We all know how unpleasant it is. Delicate machinery is interfered with and people working in factories and ordinary people at home enjoying their leisure can be affected by noise. Interviewer: Yes. Dr Hall: Even very, very small vibrations can cause parts to wear out and equipment to fail. And this is very important, all this gets added on to the price of the product. Did you know that about five to fifteen per cent of the price of a product comes from noise and vibration costs? But the usual methods used to dampen down noise and vibration rely on techniques that are thirty to forty years old. Interviewer: And what are they? Dr Hall: Well, these usually involve wrapping or covering the noisy or vibrating component with anything from cotton to concrete. But it's often very expensive and very inefficient. The performance of the noisy part also suffers as a result. Well, this is the case with the car muffler or silencer. Interviewer: And how does this differ from these new techniques? Dr Hall: The modern electronic 'anti-noise' devices don't muffle. Instead, sound is used to attack sound. Interviewer: And how do you do that? Dr Hall: Well, the trick is to hit these sound waves with other waves in a carefully controlled way. It may not be possible to eliminate noise completely, but engineers can build systems to eliminate specific kinds of noise and vibration. The new systems can deal with repetitive noise. This unfortunately means that there is not much that can be done about unpredictable noises like someone trying to play the trumpet... But the), can handle fairly regular things like engine cylinders or the sound of a turbine turning around. One new technique involves the use of a microphone and a microprocessor. The processor measures the sound and directs a loudspeaker to broadcast sound waves that are a hundred and eighty degrees nut of phase with the engine noise. The developers claim that it would make a car engine quieter and more efficient, if not one hundred per cent silent. Interviewer: Aren't there other areas of application in the noisy industrial environment of today? I mean, we're all of us affected in some way or another. Dr Hall: True. Interviewer: Whether we work in a noisy factory or not. Dr Hall: Sure. One system which the same company is developing aims to minimize the noise of aircraft engines and helicopter vibrations. The design of new aircraft engines today means that they're often more fuel efficient than earlier ones. But they're also noisier. 'Anti-noise' systems would be able to reduce noise in the cabin of an aircraft to more acceptable levels. Interviewer: That's brilliant. And how about the noisy workplace? And the effect on the workers themselves? Dr Hall: Sure. Well, people working in noisy workplaces are probably more affected by noise than anything else. 'Anti- noise' techniques can create zones of quiet in loud workplaces - well, like the one we're standing in now. You can hear the factory noise all around you, but we can still carry on a conversation without having to shout, can't we? Interviewer: Yes, but how does this work? Dr Hall: Well, to create a zone, microphones are suspended around a work station on a factory floor. Loudspeakers that generate out of phase sound waves are put close to the worker under the desk or the workbench. Well, there's one, look, over there. Yeah, yeah. And the rest of the factory remains noisy. If we just step outside the zone, you'll hear what I mean. Interviewer: OK, let's try that. Here we go... Dr Hall: See what I mean? Interviewer: Yes, let's get back inside the quiet zone, shall we?