Currently, there are two different noise-proofing strategies: active noise control using devices that emit negative sound waves, and passive noise reduction with sound wave absorbing materials.
Mechanical engineers at Boston University used a 3D printer to create a donut-shaped noise-canceling barrier. This brand new design, first constructed as a mathematical model, is capable of blocking up to 94% of the energy transmitted in the sound wave while letting air pass through. The interior of the barrier is shaped in such a way that it can literally send incoming sounds "back to where they came from". In a proof-of-concept experiment, they managed to silence a cranked-up loudspeaker by covering its outlet with the barrier. One could easily see that the subwoofers were actively thrumming away during the test.
The researchers hope to develop their invention for everyday noise-proofing tasks. For example, their design can be used to reduce noise from HVAC systems effectively, without interrupting airflow. If they can build a wall-like structure using a similar metamaterial concept, the resulted noise shield would ease the noise pollution from highway traffic and block high-pitched noise generated by MRI scanners.
Their research was published in the journal Physical Review B.