Imagine that I have a gizmo in my home not unlike a home stereo. Only this gizmo does the opposite of a stereo: rather than introduce sound into my home, it drowns out existing sound with silence. The higher I turn up the “volume,” the quieter things become. At 1, the edge is taken off ambient noise but family members can still carry on conversations. At 5, the sounds of rain, dogs barking, and other outside noises are gone and Mrs. Homie and I have to raise our voices to be heard. At 10, a passenger jet could fly overhead and I wouldn’t hear it. When it is turned off, everything resumes as normal and no damage is done to my hearing.
Has such a thing ever been attempted? Is it even possible, even in theory? The industrial applications are probably worth billions (put a bunch in a loud factory, or in neighborhoods near airports, etc.).
I’m not an expert, but noise cancellation is an imperfect example of exactly what the OP is asking about; so yes, it’s possible.
Noise cancellation works by creating sound waves that are the opposite of ambient sound, resulting in net silence, ideally. I don’t know if an adjustable version like the OP postulates has ever been made, however.
I don’t know the theoretical limits of such technology, but one important limitation I do recall is the system’s ability to predict/analyze the ambient sound, in order to produce an opposite set of soundwaves. The system has to be able to analyze and produce the opposite waves before the original reaches your ears, so it’s more effective with steady sounds ( which can be predicted ) than unpredictable ones. And by the same token it should in theory be possible to better block sounds from farther away than nearby, since there will be more time to analyze the sounds.
However, you could connect your house up to a large vacuum pump.
Too noisy? Just suck out all the air, and you have blessed silence.
Unfortunately, you’d also risk serious ear damage from sitting around in a depressurized living room.
You can’t ‘create’ silence any more than you can ‘create’ darkness, but as has already been said, there are so-called active noise control devices that essentially work by cancelling out a sound wave with its inverse.
How about the ever-popular science fiction/fantasy conceit of the “cone of silence” - an invisible barrier that stops sound from passing through? Is such a thing theoretically possible?
There are a few anechoic chambers out there, which are similar. It shouldn’t be any trouble to create a soundproof room, but you can’t cancel out the noises generated inside.
I’m giving him the benefit of the doubt and assuming he means because a receiver (or ring of receivers) can be situated a certain distance from the device to sample and analyze incoming sounds, giving the device that head start on forming a cancelling wave.
Pretty much; sorry if I was unclear. I was making a point about the fundamental limits of such a system; the farther away the sound is from, the farther away the samplers can be, and the more time the system has to work. Having the sampler fifty feet away won’t give you an edge in the speed of processing the sound if the sound is only from five feet away, after all; rather the opposite.
If the sound you’re trying to cancel is coming from far away, then far simpler and more effective than trying to analyze it before it comes and using that analysis to cancel it with precisely synchronized negative waves would be simply setting up a thick wall between you and the source.
(Not that this is always an available option, of course)
My landlord works at a large aircraft manufacturer, making devices that reduce cabin noise on passenger jets according to this principle. I talked to him about it once; they’re not perfect, but as computers get faster, they improve incrementally over time.
Here would be my question:
If you had a device at point B that could analyze and instantaneously sends out soundwaves perfectly out of phase with a noise source at point A, would the two waves be out of phase at point C?
I don’t think so because of the distance AC and BC are differen, the waves and troughs from the two sources would not cancel.
I suggest reading the short story “Silence Please” from Arthur C. Clarke’s collection “Tales From The White Hart”. A cautionary tale about an acoustic silencer, written in the 1950s.
I have heard of devices in cars that do the noise cancelling trick. The advantage they have there is that many of the noises are preictable. As well as sampling the ambient sound through a network of microphones placed as close as practical to the ears of the passengers, it also processes information from the engine.
The three sources of noise that the system predominantly deals with:
engine noise – reasonable successful cancellation
road noise – moderate success
wind – almost no success – this is essentially high frequency white noise with no predictable patterns.
I am guessing that such a system would also deal adequately with rattles that cars develop over time.
IIRC, The device was marketed at a car show where the aim was to re-introduce an artificial “engine noise” so that your Hyundai could sound like a Porsche. Anything you couldn’t cancel out was drowned out – not quite the silence I would hope for.
You’re right for any randomly picked point C. Although “perfectly out of phase” isn’t really necessary; it just needs to be out of phase to produce the nodes and anti-nodes.
If C is in line with A and B, though, a theoretically perfect device could prevent any sound from travelling directly to C from A. Imagine some sort of speaker membrane that negates the sound from one side, and no sound proceeds out the other.
It’s far easier, though, to use a dampening device to achieve a similar effect (and the technical term for that is “a wall”).
Funky looking, there’s one at the university that a few mates have performed inside.
Not quite as funky looking was the padded room Dad showed me inside the local court house, for phone calls between solicitor and client. Just nicely padded inside, the dampening effect on a normal conversation inside is slightly eerie.
