Noise-cancelling windows that block traffic sounds even when windows are open are inching closer to reality, with a new study showing that the technology can reduce perceived loudness of traffic noise by half.
Researchers from Nanyang Technological University in Singapore (with the support of the national government through the Cities of Tomorrow Research Programme) have been working on such a device to solve a common dilemma felt by households in busy tropical cities like Singapore: keep windows open and expose yourself to irritating traffic noise, or keep windows closed and swelter without cooling breezes. Not to mention the need for extra airconditioning.
Research like this is becoming increasingly important as more evidence emerges to link noise exposure to health problems. In 2018, the World Health Organisation linked chronic noise exposure to a range of health issues such as coronary heart disease, high blood pressure, annoyance, sleep disturbance and children’s learning and hearing impairment.
The new device developed by acoustic engineer Bhan Lam and his colleagues uses the same “active noise control” technology as noise-cancelling headphones. This relies on using microphones that pick up noise and speaker-like devices that then emit “anti-noises”, which are waveforms that are the inverse of the noises detected. When the noise and anti-noise converge, they cancel each another out.
The new device is made up of 24 speakers (each 4.5 cm in diameter), fixed in a grid pattern to bars on the inside of a window, with a sensor located outside the window.
This formation was able to decrease the perceived loudness of urban transportation noises by up to half (10 decibel reduction), translating to a 7 per cent to 17 per cent decrease in associated health risks.
While the device is capable of cancelling out noise at a range suitable for passing cars, trucks and trains (between 300?Hz to 500?Hz), for it to block out low-frequency noises, such as aircraft, the speakers would have to be much bigger and therefore disrupt airflow and views.
It may also struggle to block out yelling on the street because it is ineffective for frequencies higher than 1000 hertz, a range that includes human voices. While the existing device is best for consistent noises such as traffic, it may be able to be modified for inconsistent noises, such as construction site sounds.
“We hope that this active noise control system encourages the increased adoption of natural ventilation without the drawback of increasing noise exposure in cities,” said lead author Bhan Lam.
The device is on track for a pilot in real-world settings and will then face the next challenge of commercialisation.