B2 Reading Multiple Choice Exam 5
Noise pollution and antinoise
Noise pollution is excessive noise which can harm human or animal life, and can lead to hearing loss and serious stress through irritation. Most outdoor noise is mainly caused by machines and transportation systems such as motor vehicles, aircraft, and trains. Indoor noise can be caused by machines, building activities, and music performances, especially in some workplaces. It makes no difference whether noise-induced hearing loss is brought about by outside or inside noise, something needs to be done.
Antinoise is a process designed to eliminate noise. A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out. There must, however, be a perfect match, otherwise you end up with double the din. Thus anti-noise has had to wait for the microprocessor in order to be effective. The microprocessor can monitor the unwanted sound and respond in milliseconds.
It has now hit the marketplace which means that refrigerators will no longer whine, vacuum cleaners no longer roar, and washing machines no longer rumble. It may even soon be possible to cancel out the low-frequency throb of the teenage stereo blasting its bass through the wall from the flat next door. Already Toshiba has introduced a silent refrigerator. Built into the fridge is a system that silences the hum of the motor by firing anti-noise at it.
A typical active noise cancellation system has been sold to a railway company in the United States which unloads grain from trains by using giant vacuum tubes. These tubes produce as much noise as a jet taking off and after installing the system, the noise was reduced to the level of an air-conditioner's hum. Forty were installed and the people living nearby are extremely grateful.
In the aircraft industry, active noise cancellation is contributing to a revival in propeller-driven passenger aircraft, which passengers disliked because of their noise. In the car industry, conventional exhaust pipes generate back-pressure, which forces the engine to work harder. An active noise canceller removes the need for sound-absorbing chambers, and thereby improves fuel consumption by as much as six per cent. No wonder car makers are keen to install the technology. At this rate it won't be long before silent washing machines, fridges and vacuum cleaners are in the High Street shops. Electrolux has signed an agreement to manufacture the technology which should be on the market soon.
If only the bird that starts singing at 5 in the morning could be anti-noised.