I think that it works by producing an “isometric mirror image” of the incoming sound wave to “cancel” it out (as much as possible anyway since I doubt that in practice such cancellation can be perfect). Thus, if you were to “graph” the amplitutde and frequency of the incoming sound wave, and that of the produced out going sound the “hills” would be met with perfect “valleys” and vice versa. I think that Bose may offer a product that uses this technology. Does this technology actually work? Couldn’t this be employed to make “stealth suits” or at least “stealth shoes” that let you walk virtually in silence?
Here is an even more interesting question IF this is valid theory. Couldn’t the same principals theoretically be applied to “light” which also has a fequency? Thus, we should at least in theory be able to “cancel out” incoming light creating effective invisibility (at least at night since during the day canceling out all incoming light would make you appear “black” to the observer). Could we take this concept even further and cancel out “heat” or thermal energy (not sure if simple heat posesses a wave length unless we are talking about microwave or Infrared heat). However, IF we could then in theory we might be able to produce special “fire suits” for firemen tha generate a “anti heat” field enableing them to enter hotter areas and stay longer.
It works but there are some limitations to the technology. It’s easy to visualize the “peaks and valleys” of a wave in a single plane, but it gets a lot more complicated in three dimensions. In every point in space you have sound coming from multiple directions, so you get different peaks and valleys all over the place. Noise cancellation systems for a very small area like headphones works pretty well, but cancelling out noise over a larger area is a lot more complicated. The systems used in some automobiles typically use a lot of microphones and speakers with some complicated digital signal processing units in between. They also tend to run the music system through the same speakers, so as a side benefit you get a wicked cool sound system. But as far as the noise cancellation goes, it makes an audible difference in the amount of noise, but it doesn’t cancel it out completely.
Light is too high in frequency and moves too fast for us to make any similar sort of system using present technology and heat isn’t a wave.
Note that such cancellation is behind the classic Young Double Slit Experiment. But the cancelling wave has to be: Of the same frequency. Of the same phase. Of the same amplitude.
Such cancellation can be quickly generated for sound waves, but not for visible light frequencies. Just producing a wave of a given frequency and phase in an instant is well beyond our means. Note that your ideas also require sensors that can detect all three properties on every microscopic area of the surface. That is just asking way too much.
Note that you can generate (more or less) all three wave properties for radio waves, but with a delay. This can be used to jam radio waves, but the classic USSR type jammers just used a transmitter on the same frequency broadcasting noise without trying to actually cancel the signal.
And also of the same polarization, which you don’t have to worry about at all with sound.
On the other hand, as you already pointed out, the net effect of such technology (if it existed) would be to make you look black. Well, we already have a technology which will do that just as effectively. It’s called paint.
Let’s say I have a sealed room with two speakers, each facing the other. Both of them are creating a single, perfect tone, and each is perfectly out-of-phase with the other.
I ramp up the amplitude of both waves exactly in sync, to levels completely absurd. What eventually happens, assuming the speakers will not blow out or fail in any other ways?
This demonstrates the whole problem with noise cancelling technology. If the two speakers were at exactly the same point in the room (which is physically impossible), then they would cancel each other out exactly at all points in the room.
The problem is they aren’t at the same point. So at some points in the room, the two waves will cancel and make nothing. At other points in the room, the two waves will add together and you’ll get double the sound volume. At all other points in the room you’ll get somewhere in between, so in some places the sound will be lessened but in some it will be greater than just one speaker.
The second problem here is that where each of these points are depends on the frequency, which means for any arbitrary sound the points where they cancel will be different. Even worse, where the points are will also change as the weather changes. What’s important here is the wavelength relative to the distance of the two points (assuming each speaker is a point source, which is also an approximation). The wavelength is the velocity of the wave (the speed of sound in this case) divided by the frequency. The speed of sound varies slightly with the air pressure. The points where the sounds will cancel is when the total distance between the point and the two speakers is any multiple of the wavelength, since the two waves are out of phase. Any point where the distance is a multiple of the wavelength plus half a wavelength will get double the sound.
This is why for headphones, you can almost assume that the sound coming into the ears is from a big point source outside of your head, and simply sending in a cancelling wave form works fairly well. But in something like a car, it gets a lot more complicated, which is why noise cancelling systems in cars have so many microphones and speakers.