Australasian Science: Australia's authority on science since 1938

Noise Cancellation on a Larger Scale

Researchers at The Australian National University have found a way to cancel out the noise produced by motors and air conditioning units, providing some much-needed relief to anyone working or living in a noisy environment.

“What we’re looking at is cancelling the sound over an extended region, without wearing headphones,” said Prof Thushara Abhayapala. “That’s a much more difficult and complex task because it’s not just confined to the ear cup, and things reflect back from walls and around rooms.”

“We’ve come up with a technique to separate the sound going out from the sound coming in, and actually cancel the sound going out. No matter where you are around it, you get the reduced noise level.”

The system, published in the Journal of the Acoustical Society of America (https://goo.gl/g8P2bu), uses a range of microphones and loudspeakers to override the original noise source with a second sound. While it works effectively on low frequency noises, high frequency noises present a bigger challenge. When the frequency is high the acoustic wavelength is small, so cancelling them would require multiple microphones and loudspeakers. This isn’t always practical.

“You can’t cancel noise like jackhammers, unfortunately, because the frequency is too high, but boilers on top of buildings and that kind of sound you can cancel,” said PhD scholar and lead author Fei Ma.

The louder the sound, the louder the residual noise, but the technique can reduce noise by around 10 dB. This could be enough to protect hearing, as prolonged exposure to noises above 80 dB can cause long-lasting damage.