Temperatures are breaking records this summer. It is simply impossible to be on the street, but at home you want to open the window as soon as possible. However, the noise of the streets and the hum of cars can interfere with a comfortable stay in an apartment, which is why scientists have developed a special active noise cancellation system.
The sound control system can be installed on an open window, allowing the breeze to enter and the hum to remain outside. It includes a microphone to detect incoming sounds and a speaker array to suppress noise.
Currently, there are two ways to suppress noise: passive and active. The first method is quite simple, since to reduce the amplitude of the sound wave oscillation, an obstacle is placed that prevents the wave propagation. The active noise cancellation method is more complicated. It assumes the creation of another wave in antiphase, which, when "superimposed" on the first, "dampens" the sound.
Stephen Elliott, lead author of the paper, said such systems are often used to control sound in cars: "Honda, for example, makes a million cars a year with systems where they control the sound inside the cabin using sound from the speakers."
To test such a system in a living space, the scientists attached a rectangular array of 24 speakers, each 4.5 centimeters in diameter, to an open window, along with a microphone. The speakers deliberately emitted white noise, as well as the sounds of a highway, a moving train and a flying plane lasting 6-19 seconds. So scientists created a "counter" to the sounds of the street, which in turn picked up the microphone.
However, this device is not a magic wand and with it you can still hear the bell ringing on the bicycle bell. Scientists note that this happens because the method works best with low frequency sounds. The system was effective in the 300 Hz to 1 kHz range - the gap that covers most of the traffic and train noise.
