Active cancellation

[KevinDrummer]

I know that active sound canellation/reduction has been around for years for steady state and LF noise reduction - like say, for large compressors on buildings and stuff.

But with Bose's new headphones, it looks like the technology might be getting a little better. My understanding is that it works better for LF. Is that true? What are the major constraints with this technology? Is it just processing speed? Anyone have any resources on the technology?

If it does indeed work better for LF, and since LF is the hardest to isolate, would it be possible to set up some subwoofers to create the "anti-noise" in a space adjoining a loud space, only cancelling the offending noise by placing the input (mic) in the noisy space?

[Todzilla]

Kevin,

Given that sonic content changes drastically from one point to another in an acoustic environment (even with changes as little as an inch) it would seem that noise cancellation would be fruitless except where one could control the exact positioning of the listener.

Of course, there are plug-ins that analyze noise free of desired signal and can intelligently compensate for it. But even those leave artifacts.

Not sure of the application you had in mind...

[KevinDrummer]

Originally Posted by Todzilla

Kevin,

Given that sonic content changes drastically from one point to another in an acoustic environment (even with changes as little as an inch) it would seem that noise cancellation would be fruitless except where one could control the exact positioning of the listener.

Of course, there are plug-ins that analyze noise free of desired signal and can intelligently compensate for it. But even those leave artifacts.

Not sure of the application you had in mind...

Todd,

My interest is both practical and just plain curiosity. I'd like to look into the technology, but my "googling" seems to indicate this is a very much emerging tech. and everyone is keeping pretting tightlipped about it.

I didn't think about the changes in pitch, etc. that might happen in the other room. hmmm. Perhaps one could "dial in" the prob. freqs.

I'm familiar with some aspects of the plugins you describe - i.e. "vocal removers" that work somewhat but also remove all the desired low-end.

If the technology is truly emerging at a highly increased rate, would it be accurate to say that maybe in 10 years, one could not worry about isolation problems if they had the dough to spend on active cancellation - or are there real physical "walls" that will always prevent this from being a realistic solution. If so, what are those walls?

So, does anyone know about the specifics of the technology? Is it basically a PID loop?

[punkin]

The way I understand those headsets by Bose work is simple phase reversal. It hears the noise and plays it out of phase back at you. That's what I've been told anyway.

[Innovations]

That's my understanding too, here is my experience with them.

1. They add a hiss, like a soft constant static.

2. They do work better on low constant hums. That is because they have a reaction time (how could they not) and so a sudden or high frequency noise is already at your ear.

3. Because of this I would never consider them for mixing or for critical listening situations. Where I used to use them a lot was when traveling on airplanes. They did a lot to reduce the engine noise and ventillation hum.

[TexRoadkill]

Are you hoping to set up a dead area outside of a studio for isolation purposes? I can't see how it would work. My understanding is that any active noise reduction requires the dead spot to be inbetween the sound source and the NR speakers. You would have to setup the NR speakers outside the building.

One of the biggest problems with LF isolation is the mechanical vibrations and an active system won't help with that.

[KevinDrummer]

Originally Posted by TexRoadkill

Are you hoping to set up a dead area outside of a studio for isolation purposes? I can't see how it would work. My understanding is that any active noise reduction requires the dead spot to be inbetween the sound source and the NR speakers. You would have to setup the NR speakers outside the building.

One of the biggest problems with LF isolation is the mechanical vibrations and an active system won't help with that.

No, I'm not really trying to do anything with it. Just curious. Apparently some carmakers are using it now as well.