单项选择题

TEXT B
As more people live closer together, and as they use machines to produce leisure, they find that their leisure, and even their working hours, become spoilt by a by-product of their machines--namely, noise. Noise is nowadays in the news; it has acquired political status, and public opinion is demanding, more and more insistently, that something be done about it. So it was very appropriate’ that many people professionally interested in noise control should meet to discuss their common problems at a large-scale conference. In the three days of the Conference at Teddington, 25 papers were presented; and faced with the pile of texts, whose contents ranged from sophisticated aerodynamics to general comments on the irritation expressed by neighbours, it was difficult to sort out the new ideas which remain active in one’s mind six months from now, from the big mass of valuable knowledge and facts which will remain on the shelves for reference.
This difficulty was faced by Mr. D. W. Robinson, head of the acoustics work at the National Physical Laboratory. His introduction elaborated the general idea that noise must be considered in relation to the social organism which produces it. Sound becomes annoying noise only when someone’s opinion has made it so. In terms of energy, it is an undesired byproduct, often an exceedingly small fraction of the main output of the machine or process which produces it, and correspondingly difficult to reduce significantly. To control noise is going to demand much self-discipline (annoyance arises often from lack of common courtesy and imagination), a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.
Technical difficulties often arise from the subjective-objective nature of the problem. You can define the excessive speed of a motor Car in terms of a pointer reading on a speedometer. But can you define excessive noise in the same way The results of several large-scale experiments, involving numbers of vehicles and of listeners, show how difficult it is to fix any instrumental reading as a legal limit in a way which satisfies most of the public and yet is fair to the vehicle owner. You, find, for example, that with any existing simple "noise meter", vehicles which are judged to be equally noisy by a jury may show considerable difference on the meter.
A group of papers dealt with noise, at the source--the basic origins of noise in gears, internal combustion engines, fans and jets. The prospect of a significant reduction in noise output from jet engines of the future was one of the most important questions discussed at the conference. Though the ideal cure for noise is to stop it at its source, this may in many cases be impossible. The next weapon in the anti-noise armory is to absorb it in transit to the ear.
It is a common fallacy that a sound absorbent such as glass wool is opaque to sound and is therefore the best way of diminishing annoying noise from the flat next door. In a normally furnished room, lining a wall with absorbent will have little effect on the noise level built up by reverberation; and will contribute hardly anything to the acoustic opacity of the wall. In a typical factory building, even if all available surfaces are covered with absorbent, the noise level is unlikely to drop by more than five decibels. A consultant will often recommend light partitioning, and partial screening round noisy machines, as a more of the Conference at Teddington, 25 papers were presented; and faced with the pile of texts, whose contents ranged from sophisticated aerodynamics to general comments on the irritation expressed by neighbours, it was difficult to sort out the new ideas which remain active in one’s mind six months from now, from the big mass of valuable knowledge and facts which will remain on the shelves for reference.
This difficulty was faced by Mr. D. W. Robinson, head of the acoustics work at the National Physical Laboratory. His introduction elaborated the general idea that noise must be considered in relation to the social organism which produces it. Sound becomes annoying noise only when someone’s opinion has made it so. In terms of energy, it is an undesired byproduct, often an exceedingly small fraction of the main output of the machine or process which produces it, and correspondingly difficult to reduce significantly. To control noise is going to demand much self-discipline (annoyance arises often from lack of common courtesy and imagination), a sense of proportion (there is usually a conflict of interest if a noise is to be stopped), the expenditure of money (and it is far more economical to do this early rather than late), and, finally, technical knowledge.
Technical difficulties often arise from the subjective-objective nature of the problem. You can define the excessive speed of a motor Car in terms of a pointer reading on a speedometer. But can you define excessive noise in the same way The results of several large-scale experiments, involving numbers of vehicles and of listeners, show how difficult it is to fix any instrumental reading as a legal limit in a way which satisfies most of the public and yet is fair to the vehicle owner. You, find, for example, that with any existing simple "noise meter", vehicles which are judged to be equally noisy by a jury may show considerable difference on the meter.
A group of papers dealt with noise, at the source--the basic origins of noise in gears, internal combustion engines, fans and jets. The prospect of a significant reduction in noise output from jet engines of the future was one of the most important questions discussed at the conference. Though the ideal cure for noise is to stop it at its source, this may in many cases be impossible. The next weapon in the anti-noise armory is to absorb it in transit to the ear.
It is a common fallacy that a sound absorbent such as glass wool is opaque to sound and is therefore the best way of diminishing annoying noise from the flat next door. In a normally furnished room, lining a wall with absorbent will have little effect on the noise level built up by reverberation; and will contribute hardly anything to the acoustic opacity of the wall. In a typical factory building, even if all available surfaces are covered with absorbent, the noise level is unlikely to drop by more than five decibels. A consultant will often recommend light partitioning, and partial screening round noisy machines, as a more effective and a more economical course.
Domestic noises may perhaps be controlled by forethought and courtesy and industrial noises by good planning and technical improvement. But, if we are going to allow fast motor-cycles and heavy diesel lorries to pass continuously through residential and business property, the community as a whole must decide on the control it needs to exercise, for in the long run, it has got to pay for it. And if a nation is to take a leading part in modern air transport, it must enter into international agreements on the noise control measures it will impose at its airports and here the cost of any real control is immediately to be measured in millions of pounds.
Which of the following is true about noise control