题目内容
A New Headphone
The answer to a very great noise may not be blocking it out with earplugs but taking that noise and bearing it as its own game.
Earplugs have been the simple but effective way to stop noise affecting your mind, but their shortcoming is that they also block out sounds you may want or need to hear, such as music or someone talking to you.
The answer to this problem is “ active noise cancellation(抵消)” headphones that are made up of a microphone and electronics (电子装置)that take all background low-frequency (低频率) noise, turn the sound waves upside down and rebroadcast them into your ears.
The result is that all the unwanted noises around are blocked out.
In effect, one set of electronically produced around wave has sucked away the unwanted sound waves of noise.
Stand next to a busy road wearing the noise cancellation headphones and the traffic noise disappears. Sit in an airplane and the engine noise dies away. In a noisy office, the noise of office equipment, people and air-conditioning is gone. You can still , however, hear music or people talking because that sound does not have a regular pattern and so the device (装置) does not block it.
49．What is the best way to keep out the unwanted noise?
A．To wear an earplug. B．To wear a headphone.
C．To wear a microphone. D．To wear electronics.
50．Which of the following gives a general idea of how the above device works?
A．By producing low-frequency sound waves and rebroadcast them.
B．By producing new sound waves to suck away the unwanted sound waves.
C．By changing all background low-frequency noise into an irregular pattern.
D．By sucking away all the low-frequency sound waves turned upside down.
51．Suppose you are driving your friend to the airport and the car radio is on, what can't you hear if you wear a headphone?
A．The radio music and the car engine noise.
B．The noise of the planes passing overhead and what your friend says.
C．The radio music and what your friend says.
D．The nose of the car and the planes passing overhead.
