I remember, years ago, a video on TED of a guy presenting working technology for generating sound using collapsing waves from multiple sources, so you can have sound limited to desired volume or cancel noise, so you could have silence next to a busy highway, etc. He was boasting high interest from military. His page/name and the video went offline soon after.
Noise-canceling headphones without the headphone
81–90 of 122 posts
Re: Noise-canceling headphones without the headphone
#82I wonder if it is possible to mount a noise-cancelling device directly on the source of noise, for example, on a circular saw? The frequency of sound waves from a particular tool is pretty predictable and I can imagine a device with a mic or a vibrometer and speakers that clips directly to a tool and suppresses most of noise from this particular source. I've been using ANC headphones since I started woodworking in th…
It's a soundfield problem. This only works for wavelengths that are larger than the size of the emitters and the distance between them. And even then it only works well if you can get the emission pattern of your cancelling speaker exactly the same as the source.
So, assuming you had a magical beamforming speaker array around your circular saw, you'd still only be able to cancel frequencies around under 1kHz, because there's no way to get the thing in phase above that.
This is why noise-canceling earphones have much better active cancellation at high frequencies than headphones, which rely more on passive isolation until lower frequencies. They're smaller.
Re: Noise-canceling headphones without the headphone
#83I wonder if it is possible to mount a noise-cancelling device directly on the source of noise, for example, on a circular saw? The frequency of sound waves from a particular tool is pretty predictable and I can imagine a device with a mic or a vibrometer and speakers that clips directly to a tool and suppresses most of noise from this particular source. I've been using ANC headphones since I started woodworking in th…
theoretically, if the saw has constant RPM then just playing back inverted recording loudly would do it. You just need to match them in phase :)
Yes I've had a similar idea with a condo neighbor with loud bass, it must be possible to have some attachment you put on the wall to cancel it out. That would sell well
Re: Noise-canceling headphones without the headphone
#84To me, it seems pretty obvious this can't work. The cancelling signal from your seat will have to be cancelled by all the other seats and vice versa, creating a feedback loop.
Re: Noise-canceling headphones without the headphone
#85Edit: they cheated, this isn't ANC and will never work as ANC. See below. This sounds pretty fundamentally different from normal ANC. A common misconception is that ANC headphones "predict" the incoming noise and cancel it (and thus "they're good with constant noise but not sudden changes"). In reality they're just hybrid open-loop/closed-loop feedback systems. Specifically, the mic inside the cavity works with the s…
The actual study is here [0] and the abstract and introduction do a much better job of describing what the study is actually about.
I encourage you to read at least those before you dismiss the research and its real-world applications.
TL;DR: The purpose of the research is to try out a new way of figuring out which sound is going into the user's ears, so that it can be cancelled out. Current methods work for lower frequencies but not for higher frequencies.
They "cheated" because they're testing one component of the system and the "cheating" component is immaterial to the research they're doing.
Re: Noise-canceling headphones without the headphone
#86Edit: they cheated, this isn't ANC and will never work as ANC. See below. This sounds pretty fundamentally different from normal ANC. A common misconception is that ANC headphones "predict" the incoming noise and cancel it (and thus "they're good with constant noise but not sudden changes"). In reality they're just hybrid open-loop/closed-loop feedback systems. Specifically, the mic inside the cavity works with the s…
The actual study is here [0] and the abstract and introduction do a much better job of describing what the study is actually about. I encourage you to read at least those before you dismiss the research and its real-world applications. TL;DR: The purpose of the research is to try out a new way of figuring out which sound is going into the user's ears, so that it can be cancelled out. Current methods work for lower fr…
They "cheated" because they did the easy part, and the "other component" has no known solution.
What they're handwaving away is the real problem. The reason why current methods work for lower frequencies and not for higher frequencies is that your microphone, emitter, and ear all need to be enclosed within a volume Once you put the ears in open air and the emitters away from them, the problem isn't figuring out the sound that's going into the users' ears, it's figuring it out in advance. The ANC speakers have to send the complement signal before the original signal arrives at the ears, so they both arrive coincidentally.
In other words, the "missing part" to make this research work is time travel (if you use their sensing technology as the only input). Or maybe full-volume sound field sampling and characterization technology (if you don't). Neither of which exist, and which are orders of magnitude more difficult than this research.
The handwave part is "The constraint of the possible locations [of microphones] would affect the control performance and this remains a topic to be further studied in the ANC community."
Yes, it would completely destroy high frequency performance, which is what they were trying to achieve, in anything but lab scenarios (such as the sound sources still being loudspeakers and the microphones being directly in line between them and the user). Real world noise doesn't come from loudspeakers, it comes from all around you. Good luck using distant microphones to compute the expected sound at a user's ear in advance, with any kind of accuracy in the high frequencies.
At best I imagine they could achieve adaptive cancellation for a set of slowly moving pointlike sources in an otherwise simple room, with a number of microphones greater than the number of sources. It's like RF MIMO systems. But again, this is orders of magnitude more work to implement, and real world constraints are going to kill your high frequency response. And for larger sources - forget it. You just can't characterize the transform for that. Not enough dimensions in your input data to solve for it. So anything mechanical, stuff where the noise isn't coming from a literal speaker with a 1-dimensional input signal - nope. As the uncertainty and source size grows, your high frequency response goes down the drain.
Re: Noise-canceling headphones without the headphone
#87Always great to see development in this domain. IWAENC and Silentium come to mind as the forefront. I hope one day the researchers will realize that they are trying to cancel the wrong source. Instead of cancelling noise external to the human, the real breakthrough will be to cancel the human voice. This will confer privacy and other benefits in areas of increased population density. I would prefer a smartphone to ha…
>I hope one day the researchers will realize that they are trying to cancel the wrong source. Instead of cancelling noise external to the human, the real breakthrough will be to cancel the human voice.
Only few care for the latter and millions/billions care for cancellation of external sources.
Besides, "cancelling the human voice" would just provide a false sense of security, as said voice would still need to be received by others -- and like any message it could be intercepted.
Re: Noise-canceling headphones without the headphone
#88Always great to see development in this domain. IWAENC and Silentium come to mind as the forefront. I hope one day the researchers will realize that they are trying to cancel the wrong source. Instead of cancelling noise external to the human, the real breakthrough will be to cancel the human voice. This will confer privacy and other benefits in areas of increased population density. I would prefer a smartphone to ha…
> the real breakthrough will be to cancel the human voice
If you want to cancel another human, just build a wall.
Re: Noise-canceling headphones without the headphone
#89Earlier quoted context omitted.
I don’t think this is even possible. Noise canceling works by creating reverse waves that hit your ears at the same time. You have to be able to calculate how long it will take for those waves to hit each set of ears and be able to direct sound at them.
Right, but the speed of sounds is slow. So things like placing a microphone 6 feet closer to the source allows for much more effective noise cancellation. Current tech in earphones skips that by using past noise as a prediction of future noise, and as a result only works on near constant noise of airplanes and other near constant sources of noise.
> only works on near constant noise of airplanes and other near constant sources of noise.
That is simply not true - at least in my experience with an old model of Sony headphones. It's possible that prediction plays some role, but I bought mine with specific purpose of silencing neighbor's kids.
They work really well with this kind of sporadic, random noise and the difference between turning on active cancellation and just passive attenuation due to ear muffs is very noticeable. I'm talking about low-frequency noises that are mostly transmitted through the vibrations in the walls and floors - feet hitting the floor while running, ball bouncing of the walls and so on.
Re: Noise-canceling headphones without the headphone
#90Edit: they cheated, this isn't ANC and will never work as ANC. See below. This sounds pretty fundamentally different from normal ANC. A common misconception is that ANC headphones "predict" the incoming noise and cancel it (and thus "they're good with constant noise but not sudden changes"). In reality they're just hybrid open-loop/closed-loop feedback systems. Specifically, the mic inside the cavity works with the s…
> This works for wavelengths smaller than the cavity size
(A) "This" works for a wavelength > and above a certain frequency all you have is passive muffling
(B) "This" does not work for a frequency > F. (B') "This" works for a frequency ---
Don't A and B' (or B) contradict each other? Because an upper limit for the wavelength equates to a lower limit for the frequency - not an upper limit.
What is your background that justifies your very confident demeanour?