High-Tech Window Cling is Like a Volume Knob for Real Life
gajitz.com
gajitz.com
> With its concentric broadband antenna rings, it harvests the energy of electromagnetic noise from Wi-Fi, and similar signals and this way also reduces the level of e-smog pollution in your environment.
facepalm. This is nonsense.
I always thought the only way of doing this would be to have detached microphones positioned between the speaker and the target noise so the system has enough time to compute the inverse of the incoming waves and send them out with enough space to cancel in the correct phase.
But a good concept and hard work (and hope) usually lead to quite good products...
I.e. noise cancellation in building is usually approached through "get better insulation", not through the plausibly cheaper "let's spread a speaker/mic array inside/outside to cancel what's coming form outside".
Geometry
The mic/speaker assembly are in the middle of the window but the window has substantial size relative to the dimensions of the room and the distance the listener is from the device. What this means is that you have a multipath problem; the original sound can come through the whole window (even the wall!) but the canceling sound can only eminate from the speaker.
If you draw a straight line from the original noise source, through the device and from there it happens to head towards your ears, this can work. If not things will get jumbled up and it might cancel or it might actually reinforce the noise, rather than cancelling it.
http://en.wikipedia.org/wiki/Loudspeaker#Directivity
Physics
A speaker is a device that works as a derivative of the original signal. That means it needs some amount of "advance notice" of the sound in order to be able to create the proper pressure wave to cancel out said sound. The "advance notice" is usually done by means of some distance between the microphone and the speaker but the device is very thin. Worse, the amount of "advance notice" depends on the frequency of the sound which generally makes it an intractable problem to solve for the transient case.
http://www.customanalogue.com/elsinore/elsinore_19.htm
So what people do is focus on periodic noises like hum, hiss, buzz, rumble, what-have-you. In this case you don't need to make sure that any one peak has it's inverse reproduced perfectly, you only have to ensure that ONE peak is cancelled out by SOME OTHER out of phase peak. If it takes a couple of cycles for the computer to catch on, no big deal that's just a bit of start-up noise. Bose headphones don't IMMEDIATELY make the plane quieter, they just do it so fast that you don't notice the amount of time it takes for the system to warm up. It seems instant even though it's not.
But what this means is that a bunch of the sounds being cancelled out probably wouldn't be cancelled out quite so nicely as a lot of them are transients like the bottles breaking or the construction site or the park.
I'd really love to be wrong about this. There's a joke that goes "An engineer will tell you it's impossible until you show him how to do it. Then he'll say it's obvious." It's entirely possible that this guy has figured something out that the rest of us haven't. But I will remain skeptical until I can actually put my hands on one and benchmark it for myself
The mic/speaker assembly are in the middle of the window
but the window has substantial size relative to the
dimensions of the room and the distance the listener is
from the device.
http://en.wikipedia.org/wiki/Loudspeaker#Piezoelectric_speak...
Really, fellas? I don't mind a discussion on how it could possibly be done, but where's your rudimental critical thinking? Even reddit had a better discussion [1].
[1] http://www.reddit.com/r/gadgets/comments/1pdfb0/volume_knob_...
Of course, there's one question the article didn't address: what proportion of sound is actually transmitted through window panes? One would expect that a whole lot of low-frequency sounds (traffic) would come through the walls too.
To see why this is useful, imagine a song you wanted to listen to that was recorded with a low-pitch hum in the background because the microphone running next to a power cable and picked up the 60 Hz signal. Removing this unwanted tone by looking at the value of the song in time is really hard because the 60 Hz signal is mixed up with the rest of the song. However, when transformed into the frequency domain, the 60 Hz hum is very easy to spot and remove. When you transform the signal back into the time-domain (so you can listen to it), the 60 Hz will still be gone.
This process can be done automatically with computers using a technique called the Fast Fourier Transform. This is the basis of many techniques in the field of Digital Signal Processing (DSP) which is the theory behind most of the communication breakthroughs of the last 40 years. I should note that many naive approaches to this problem (like the approach in my example) don't work particularly well, so as in any problem domain, there are important but subtle performance trade-offs to consider.
Years ago I wanted to splice a noise canceling headphone into one of these devices and make the windows noise canceling. Would that even be feasible?
I just don't believe this concept could work the way the video demonstrates it. Nice interface though... but that's kind of the easy part.