Sound moves form its source to the ear by wavelike fluctuations in air pressure, something like the crests and troughs of ocean waves. Once way to keep from hearing sound is to use ear plugs. Another way is to cancel out the sound with anti-sound. Using a noisemarker controlled by a microprocessor, engineers have produced sound waves that are half a wavelength out of phase with those of the noise to be quieted-each crest is matched to a trough, and vice versa. Once the researchers have recorded the offending sound, a microprocessor calculates the amplitude and wavelength of sound that will cancel out the crests and troughs of noise. It then produces an electric current that is amplified and fed to a loudspeaker, which produces antisound and wipes out the noise. If the anti-sound goes out of synchronization, a microphone picks up the leftover sound and sends it back to the microprocessor, which changes the phase of the anti- sound just enough to cause complete silence.

   The research team has concentrated on eliminating low-frequency noise from ship engines, which causes fatigue that can impair the efficiency and alertness of the crew, and may mask the warning sounds of alarm and fog signals.

The researcher mentioned in the passage are concerned about unwanted noise because it can_________.

Câu hỏi liên quan

• How did Juliette Davidson benefit from the experience of her first job?

• It can be inferred from the passage that John Adams was: 

• What will the speaker probably discuss next?

ZUNIA12

• The passage would be most interest to...

• Which of the following is closest in meaning to “frigid” in paragraph 1?

• The word “they” in paragraph 5 refers to .............

• Today’s students with the aid of computer__________

• According to the passage, an exuberant tone of voice may be an indication of a person's _______.

• What causes dodder to grow in a particular direction?

• Why is noise difficult to measure?

• When was M.L. born?

• The man mentioned in the passage, who used his cellphone too often, ______.

• What is the main topic of the passage?

• According to the text, all of the following sentences are true EXCEPT _____.

• Applauding was cited as an example of ____________.

• What did the five campers do when they saw a group of apelike creatures?

• What does the author imply about the rate hummingbirds’ wings beat?

• The word “ball” in paragraph 2 probably means ............

• It can be inferred from the passage that after getting married, .............

• The author of the passage argues that ...............