Noise cancellation for fun or profit

[Boy Howdy]

I'm not sure this is in the right place, but here goes anyway.

I live on the noisiest street on planet Earth. I'm tired of earplugs and brown noise CDs. I'm starting to think on noise cancellation. Does anyone know anything about this subject?

I understand the idea of phase cancellation from putting guitar pickups out of phase and such. But the only setup I can imagine possibly working would feature: a microphone to pick up the outside noise, then an amplifier, then two speakers wired out of phase with each other. The in-phase speaker could have the cone removed so it would produce no sound.

Does this sound like it would work? Can anyone improve on this idea, or suggest alternative setups?

[Helmholtz]

I don't understand the out-of-phase speakers idea.
The noise cancelling sytem needs to produce a sound that is out-of-phase with the outside noise and thus cancels it in your ears. But I'm sure details are tricky.

[Mick Bailey]

Take a look here;

https://www.youtube.com/watch?v=MCW5HUkrr-o

Towards the end he describes why noise cancelling in a room is flawed.

[Boy Howdy]

To Helmholtz: The idea was that the noise from outside would be in phase and unamplified. The amplified noise would be out of phase and adjustable for volume, theoretically cancelling some of the noise.

[Boy Howdy]

I've seen that before. I forgot about it. I'll have to check it out again.

But surely there's a way to make this work.

[Helmholtz]

To Helmholtz: The idea was that the noise from outside would be in phase and unamplified. The amplified noise would be out of phase and adjustable for volume, theoretically cancelling some of the noise.

But that wouldn't require two out-of-phase drivers.

Anyway, full spectrum cancellation will only work within a small space (preferably your ears - so headphones). Reason is that the phase of sound waves varies with position and wavelength, so two coherent sound fields in a room will produce a spatial interference pattern. Each frequency would have a different interference pattern, meaning that at some spot some frequencies might cancel while at other spots the same frequencies will be intensified.
Another concern is that the microphone needs to be placed close to the driver to avoid spatial phase shift. That in turn requires efficient acoustic screening to avoid feedback.

I think NC can only work satisfactorily if it's integrated into headphones.

[Jazz P Bass]

Your best bet is to treat the room.
https://www.bing.com/search?q=reside...ANCMS9&PC=U531

[tubeswell]

But that wouldn't require two out-of-phase drivers.

Anyway, full spectrum cancellation will only work within a small space (preferably your ears - so headphones). Reason is that the phase of sound waves varies with position and wavelength, so two coherent sound fields in a room will produce a spatial interference pattern. Each frequency would have a different interference pattern, meaning that at some spot some frequencies might cancel while at other spots the same frequencies will be intensified.
Another concern is that the microphone needs to be placed close to the driver to avoid spatial phase shift. That in turn requires efficient acoustic screening to avoid feedback.

I think NC can only work satisfactorily if it's integrated into headphones.

This is pretty much why noise cancellation won’t work in a room.

you’d need a ‘smart’ noise cancelling system that detected the 3 dimensional spatial position of each listeners Pair of Ears and was calibrated to the peculiarities of each listener’s hearing, and was able to detect the spatial and temporal location of each node and anti node at each frequency, so that the Noise cancelling generators could be continuously adjusted so the noise cancelling sound-wave anti nodes met at the precise location of each listener’s ears, or some such contrivance

[Boy Howdy]

But that wouldn't require two out-of-phase drivers.

Anyway, full spectrum cancellation will only work within a small space (preferably your ears - so headphones). Reason is that the phase of sound waves varies with position and wavelength, so two coherent sound fields in a room will produce a spatial interference pattern. Each frequency would have a different interference pattern, meaning that at some spot some frequencies might cancel while at other spots the same frequencies will be intensified.
Another concern is that the microphone needs to be placed close to the driver to avoid spatial phase shift. That in turn requires efficient acoustic screening to avoid feedback.

I think NC can only work satisfactorily if it's integrated into headphones.

Yeah, I thought that might be a problem, but had hoped it might work a little.

I couldn't think how to get two signals out of phase with one another without two speakers, And since you already have an in-phase signal coming from the outside noise source, my brilliant idea was a dedicated in-phase speaker with no cone so it would not just amplify the outside noise.

. . .CURSES! Foiled again.

[Enzo]

And for it to work, the pickup would have to be mounted on your head. A microphone on the table might pick up ambient sound and allow a cancelling signal at that table, but siting across the room, all those phase cancellations would not apply.

[Jazz P Bass]

In high end autos they use multiple microphones and a computer.
The noise is sorted out by an algorithm and the antiphase is played through the sound system.
In your case you would have to stay in one spot and not move. (being on the wrong 'lobe' of the sound wave will actually increase the sound)

I would look into window treatments first.
Window plastic to keep out drafts would put up an air buffer at the glass.
Heavy drapes would also help.

[Helmholtz]

As I've been told there are good active NC headphones. I guess each ear needs its own microphone.

[Leo_Gnardo]

In high end autos they use multiple microphones and a computer.
The noise is sorted out by an algorithm and the antiphase is played through the sound system.

It's not exactly a new technology in airplanes - I've been on a couple of Bombardiers with cabin noise suppression and they were surprisingly quiet - that was 15-20 years ago. I'm sure other manufacturers have picked up on noise suppression by now.

Another trend in autos - noise making for electric cars. So you can let pedestrians know you're there. Or just make kool noises vroom vroooooom!

[Boy Howdy]

In high end autos they use multiple microphones and a computer.
The noise is sorted out by an algorithm and the antiphase is played through the sound system.
In your case you would have to stay in one spot and not move. (being on the wrong 'lobe' of the sound wave will actually increase the sound)

I would look into window treatments first.
Window plastic to keep out drafts would put up an air buffer at the glass.
Heavy drapes would also help.

Not an option that works for me, unfortunately. Low frequency noise is my issue, which needs heavy, hard mass to stop. And my main room has too many windows and doorways for anything to be very effective.

[Boy Howdy]

And for it to work, the pickup would have to be mounted on your head. A microphone on the table might pick up ambient sound and allow a cancelling signal at that table, but siting across the room, all those phase cancellations would not apply.

I already have a pickup mounted to my head. Doesn't everybody? Damn government!