Scientists Say You Can Cancel the Noise But Keep Your Window Open (nytimes.com)
- Reference: 0133324460
- News link: https://entertainment.slashdot.org/story/20/07/13/2239248/scientists-say-you-can-cancel-the-noise-but-keep-your-window-open
- Source link: https://www.nytimes.com/2020/07/11/science/windows-street-noise.html
> Researchers in Singapore have developed an apparatus that [1]can be placed in a window to reduce incoming sound by 10 decibels . The system was created by a team of scientists, including Masaharu Nishimura, who came up with the basic concept, and Bhan Lam, a researcher at Nanyang Technological University in Singapore. Their results were [2]published on Thursday in Scientific Reports . The prototype is not yet the most practical device in real world conditions, but it points the way toward the development of technologies that may help ease the strain of noisy city living.
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> Borrowing from the same technological principles used in noise-canceling headphones, the team expanded the concept to fit an entire room by placing 24 small speakers in a window. The speakers emit sound waves that correspond to the incoming racket and neutralize it -- or, at least some of it. The system is based on the frequency of the sound waves and, for now, the optimal range is between 300 and 1,000 hertz. [...] The system uses a microphone outside the window to detect the repeating sound waves of the offending noise source, which is registered by a computer controller. That in turn deciphers the proper wave frequency needed to neutralize the sound, which is transmitted to the array of speakers on the inside of the window frame. The speakers then emit the proper "anti" waves, which cancel out the incoming waves, and there you have it: near blissful silence.
Unfortunately, there are some limitations. The system works best from the types of steady noise sources found within the optimal frequency range and isn't great at neutralizing sporadic noises. Also, since human voices don't fit within most of that range, they won't be canceled out.
[1] https://www.nytimes.com/2020/07/11/science/windows-street-noise.html
[2] https://www.nature.com/articles/s41598-020-66563-z
Could make for some chilling movie scenes (Score:2)
I am imagining some apocalyptic event happening outside someone's window and they don't even notice because of something like this. Or a person's child screaming for help right outside while they casually make dinner.
It's also kind of a pretty apt metaphor for modern society: try to block out what is going on right outside your window as much as possible so that you can focus on more important things (like the latest twitter trends, etc.).
Sorry. That's enough cynicism for today.
Re: (Score:2)
The apocalyptic concern isn’t an issue, as active noise cancellation systems do not reduce sound pressure levels. This means that a person can genuinely believe the room is silent but be going deaf - or worse.
Re: (Score:1)
> active noise cancellation systems do not reduce sound pressure levels
Is this true? How? Please clarify, because I don't believe you and I fear I'm wasting effort trying to understand.
Thus... (Score:2)
Synthetically amplifying any sound over 1000Hz, which is a lot of the sound that bothers people in cities (aka taxi horns).
Maybe more distant microphones could help (Score:2)
It's interesting it only works in such a limited range...
I was wondering if it might work a lot better, if you had several microphones oriented well away from the window at different locations - so you could get directional information on sound, which might in turn use differently oriented speakers to help cancel out particular sounds better coming from different directions.
Or, maybe speakers located at these of the bed facing the window would have a more advantageous position to cancel out noise - then you
Wavelength is the problem for higher frequencies (Score:2)
The systems work by producing the same same sound wave, but in opposite phase.
For a low-frequency sound, the wave is over 10 meters, so the air pressure rises and falls in the entire room and the device can counteract that by doing the opposite.
For high frequency sounds, the wavelength is several millimeters, so the pressure is rising in one of your ears while it's falling in the other ear. There is really to way to counterbalance that with speakers a few meters away. Maybe if you had a million microphones
Re: (Score:3)
Of course two layers of glass, say 6mm and 8 mm with a 50mm airspace between will do a lot more permanently. Now add in a duct, a filter and a small fan and suck in outside air past a filter and blow it in (use a solar panel to power the fan), cleaner and more reliable (when the winds do not blow). Fixed windows and ducted air is probably more sound in reality, health wise and environmentally.
Re: (Score:3)
No, you can absolutely cancel the sound at an arbitrary location from the source of noise and the cancellation transducers. You just need to track the listener's position accurately. And then accept that everyone else in the room will have a significantly degraded (louder) experience. But you can cancel anywhere you want - it's just a matter of getting the phase correct at the receiver (listener) position.
And yes, I design audio products - including ANC headphones - for a living.
Re: (Score:2)
> I was wondering if it might work a lot better, if you had several microphones ...
It works best if you simply roll your windows all the way up and use the A/C. :-) Besides, the Mythbusters already demonstrated that cars (theirs anyway) got better mileage with the windows up and A/C on.