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Sound solutions to low-frequency noise

By Gerald Ondrey |

Low-frequency noise (≤500 Hz) from various sources, such as construction machinery and aircrafts, is a form of noise pollution that transmits over long distances and disturbs the surrounding area. It is also known to trigger several negative physiological reactions, such as changes to blood pressure, vertigo and breathing difficulties, even when the noise is not audible. Currently, most commercially available noise-cancelling devices and structures are only effective in reducing high-frequency noise, while low-frequency noise continues to penetrate. Therefore, to more effectively mitigate low-frequency noise, a team of mechanical engineers from the National University of Singapore (NUS; www.nus.edu.sg) has designed a set of effective noise-attenuating blocks.

Described in a recent issue of Acoustics, the 3-D printed blocks can be customized to cancel a specific noise frequency by adjusting the size of the air cavity and the neck opening within the block. The blocks can then be slotted into a grid-like host structure to function as a noise barrier. Laboratory studies showed that the modular design was capable of canceling low-frequency noise below 500 Hz by an average of 31 dB. This is said to be six times more effective than other commonly used noise barriers, and the barrier is lighter and thinner than commercially available devices. Using this modular design, the NUS engineers are able to better control the properties of the noise barrier and produce them affordably.

“These noise-reduction blocks can be easily incorporated as part of existing wall structures, and it would not be necessary to build a host structure from scratch in order to implement the sound barrier,” explains NUS Mechanical Engineering associate professor Lee Heow Pueh. “Such a modular design also means that a variety of blocks targeting different noise frequencies can be used within the same host structure to effectively block a range of low-frequency noise.”

The team also developed Noise Explorer, a mobile application capable of accurately tracking noise data based on a new method of calibrating the microphones of smartphones.

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