Anyone who lives on a busy street knows the problem: as soon as the window is opened, not only air comes in, but also a lot of noise. An international research team led by Bhan Lam from Nanyang Technological University in Singapore came up with a solution. The window should play back noise to eliminate noise. In Scientific reports the research results were published.
The working group attached 24 small loudspeakers directly to the open window in order to eliminate the sound entering from outside. The reason for the placement at the window is that the street noise should ideally be combated at the point where it penetrates the apartment.
The basic principle is similar to how Active Noise Canceling (ANC) works in headphones, i.e. active noise suppression. The systems are designed to eliminate noise by playing a suitable counter sound and ideally neutralizing the noise source.
Special windows required
The experiment was developed for apartments in Singapore, where there are often metal struts on the windows. These struts were used to mount the 24 loudspeakers across the window area. If you do not have metal struts in front of the windows, you will have difficulty distributing the speakers over the window area. The system does not necessarily make the outlook more attractive. When you look out of the window, you can see a lot of speakers. The whole thing is called an anti-noise control window.
To measure the external noise, there is a microphone on the outside of the window with which the sound waves are analyzed so that the appropriate counter-sound can be played through the loudspeakers. The microphone and loudspeakers are controlled by a computer system that does all the necessary calculations. This is intended to eliminate sound waves in the range between 300 and 1,000 Hertz.
Active noise reduction should keep out a lot of noise
If the active noise suppression is activated in the corresponding room, there should be a similar effect as with ANC headphones: background noise is at least strongly attenuated or even completely suppressed. Ideally, the Anti-Noise Control Window could keep the outside noise so far away that the noise level corresponds to that when the window is closed.
Especially monotonous sources of noise can currently be suppressed well. Conversations, however, have so far been difficult to filter. It also hardly reduces the sound of sirens or fireworks. The restrictions also have to do with the size of the speakers installed. In order to be able to filter out more frequency ranges, significantly larger speakers would be required. According to Lam, these would have to be housed in the window and that would affect the air exchange even more than it already does, according to a report from New York Times.