Researchers from Singapore have developed an active sound control system which can be fitted to an open window to reduce observed sound coming from outside a building.
The team behind the system recently published a paper on their work in Scientific Reports.
Essentially, the device functions like noise-cancelling headphones for buildings located in cities, allowing their occupants to keep the windows open without having to deal with loud sounds emanating from traffic, construction, alarms, and other sources.
This can be especially beneficial in densely-populated, high-rise cities with climates that require natural ventilation to increase comfort and lower the health risks of constantly using air conditioning systems.
It employs a reference microphone directed towards the outside of a building, which captures exterior sounds and provides advanced information to a controller to compute an anti-noise signal.
This is then sent to an array of small loudspeakers, the control units, directed towards the inside of the building. These speakers actively attenuate the incoming sound by producing an appropriate anti-noise signal.
For the experimental prototype of their device, the researchers constructed a mock-up room with a 1m x 1m window and installed a system with 24 speakers placed on its security bars.
They then placed a large loudspeaker 2m away from the window to recreate loud city sounds, as measured in real-world conditions in residential buildings.
Within the room, they used an array of seven observation microphones to measure the energy-averaged sound pressure levels, in accordance with the necessary ISO standards.
The results of their tests showed that a reduction of at least 10dB was attainable for noises up to 1kHz.
As a control test, they also closed the window and found that while it still worked better for reducing the noise levels, the difference was only between 2.22 dB to 6.39 dB.
Below is a schematic of the room and image of the system which the researchers developed.