Worthy Of Consideration: ANC(Active Noise Cancellation) on the Road
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TheSonicTruth

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Worthy Of Consideration: ANC(Active Noise Cancellation)

Within the last twenty years, with or without carmakers calling attention to it in driver/consumer literature, various systems have been introduced into factory car audio systems to minimize or cancel out engine and other noise in the passenger cabin.

This capture, from the service manual for the Eighth-Gen. Honda Accord(2008-2012), explains the concept and implementation in lay-terms.

Your thoughts?

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SilverEars

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I think it's worthy to implement this, but of course you'd have to give it a test run to see how effective it is. ANC isn't effective for random sounds particularly quicker high frequencies. It will reduce the cyclic noise like on engines and so on. This is why ANC is very practical in airplane cabins as the loudest majority noise is the engine noise. So yes, for engines it makes sense to implement. I would enjoy car audio with more coherency from it.
 
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bigshot

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I would also think that it's a lot easier to do this in headphones that are enclosed and controlled than it is in a car cabin where every seat is getting different sound and different noise.
 
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old tech

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Many new cars have ANC technology incorporated in them - typically the more premium brands, but it is filtering its way through other makes.

Not sure how well it works though. I've been in a couple cars with that technology and it is not really apparent if they are any quieter than other similar vehicles that do not have it.
 
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TheSonicTruth

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For those here in favor of it, I have an even simpler and better form of 'Active Noise Cancellation' - it's called a VOLUME KNOB. Couple with the option of installing adhesive sound-deadening material on the interior firewall, or doors, floor, etc.

In my car's case, it's not a user-adjustable/defeatable menu item(such as Speed-sensitive volume).

I have to remove half of the forward trim(center console, partial dash) to get at either the back of the radio or the actual ANC module to unplug it. The module is supposedly slightly bigger overall than a classic Zippo brand cigarette lighter. Disabling it in diagnostic mode from the radio front panel it just resets the next time one gets in the car and starts it up.

I'm pretty sure it's contributing to a massive 150-200Hz hump in my factory stereo's listening response, and from what I've read in forums relevant to my make and model of vehicle, the only reported effect of disabling ANC is both a more neutral sound, tone controls that actually do something to the sound, plus higher output. Something I'm looking forward to!

The reports also suggest that just disconnecting the microphones(front and rear cabin) is nothing more than filing a couple inches off the horns of an angry Bull - the ANC is still active and sapping energy from the stereo head unit.

I'm just not sure if I'm capable of dismantling and reinstalling half my dash to accomplish that.
 
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gregorio

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The problem is that the published diagram shows how the principle of phase cancellation works, NOT what is actually happening with their ANC system. To explain:

If we say the peak value of the sine wave (representation of noise) is +50 and the trough is -50, then if the peak of the noise occurs at exactly the same instant as the trough of the generated cancellation signal we get +50 + (-50) = 0, complete cancellation of the noise and cancellation signal. However, if they don't occur at the same instant, say the cancellation signal is delayed by the equivalent of quarter of a cycle (IE. We move the generated signal to the right by quarter of a wave cycle), we've now got the peak of the noise at +50 at the same instant in time as the generated signal is at -25, so we've reduced the noise by half, +50 + (-25) = 25, not cancelled it. Worse still, if we delay the generated signal by exactly half a cycle we've now got the peaks and troughs of the noise and cancellation signal occurring at the same instant, +50 + (+50) = 100, double the amount of noise!

So why would the generated signal be delayed and what are we actually talking about in real terms? The noise signal has to be picked up by a mic, sent to a processor, a cancellation signal calculated and generated, then sent to your speaker and then the sound wave has to travel from your speaker to your ears. All of this this is going to take more time than it takes the noise to reach your ears. In real terms, a 200Hz sine wave (for example) completes a cycle in 5 milli-secs, so half a cycle is 2.5ms and sound travels at just over a foot a milli-second. So, not even considering the processing/generating delay, if your head were about 3ft further from the speaker, instead of noise cancellation you'd have the exact opposite, double the amount of noise! And, the processing time is likely to take at least a milli-sec or so.

This of course is a simplification, there are a lot of variables and with careful mic positioning and clever freq compensation, you could in theory get very close to or actually achieve complete cancellation but on the other side of the coin: That's with one speaker and one head position (relative to that speaker). In practice, if your seat (or seat back) is set to any position other than that calculated (presumably for the average driver), the cancellation will be compromised, plus of course we've got more than one speaker which are at different distances relative to the driver's head and, unless the system is designed for ANC only for the driver, two or more quite different head positions. In practice, a well designed and implemented system should give a decent reduction in noise but if it's not so meticulously designed/implemented and/or if your head position is some distance from point calculated for the average driver, then you might not get any noticeable reduction in noise and possibly even an increase in those generated freqs. We're only talking about tiny slivers of time and fairly small distance differences making a relatively large difference to the summed sound wave entering your ears.

For the above reasons, I'd be very careful about what I "read in forums" from other owners. They probably don't know the principles or variables involved and even assuming their perception is accurate, a say 150Hz-200Hz hump for one owner could be a relatively flat response (with reasonable noise reduction) for another, depending on their seating position for example. As @bigshot stated, it's a whole lot easier with headphones, the distance between the HP drivers and the user's ear drums aren't significantly different between different owners, no more than a fraction of an inch or so, rather than potentially a couple of feet or so.

G
 
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TheSonicTruth

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The problem is that the published diagram shows how the principle of phase cancellation works, NOT what is actually happening with their ANC system. To explain:

If we say the peak value of the sine wave (representation of noise) is +50 and the trough is -50, then if the peak of the noise occurs at exactly the same instant as the trough of the generated cancellation signal we get +50 + (-50) = 0, complete cancellation of the noise and cancellation signal. However, if they don't occur at the same instant, say the cancellation signal is delayed by the equivalent of quarter of a cycle (IE. We move the generated signal to the right by quarter of a wave cycle), we've now got the peak of the noise at +50 at the same instant in time as the generated signal is at -25, so we've reduced the noise by half, +50 + (-25) = 25, not cancelled it. Worse still, if we delay the generated signal by exactly half a cycle we've now got the peaks and troughs of the noise and cancellation signal occurring at the same instant, +50 + (+50) = 100, double the amount of noise!

So why would the generated signal be delayed and what are we actually talking about in real terms? The noise signal has to be picked up by a mic, sent to a processor, a cancellation signal calculated and generated, then sent to your speaker and then the sound wave has to travel from your speaker to your ears. All of this this is going to take more time than it takes the noise to reach your ears. In real terms, a 200Hz sine wave (for example) completes a cycle in 5 milli-secs, so half a cycle is 2.5ms and sound travels at just over a foot a milli-second. So, not even considering the processing/generating delay, if your head were about 3ft further from the speaker, instead of noise cancellation you'd have the exact opposite, double the amount of noise! And, the processing time is likely to take at least a milli-sec or so.

This of course is a simplification, there are a lot of variables and with careful mic positioning and clever freq compensation, you could in theory get very close to or actually achieve complete cancellation but on the other side of the coin: That's with one speaker and one head position (relative to that speaker). In practice, if your seat (or seat back) is set to any position other than that calculated (presumably for the average driver), the cancellation will be compromised, plus of course we've got more than one speaker which are at different distances relative to the driver's head and, unless the system is designed for ANC only for the driver, two or more quite different head positions. In practice, a well designed and implemented system should give a decent reduction in noise but if it's not so meticulously designed/implemented and/or if your head position is some distance from point calculated for the average driver, then you might not get any noticeable reduction in noise and possibly even an increase in those generated freqs. We're only talking about tiny slivers of time and fairly small distance differences making a relatively large difference to the summed sound wave entering your ears.

For the above reasons, I'd be very careful about what I "read in forums" from other owners. They probably don't know the principles or variables involved and even assuming their perception is accurate, a say 150Hz-200Hz hump for one owner could be a relatively flat response (with reasonable noise reduction) for another, depending on their seating position for example. As @bigshot stated, it's a whole lot easier with headphones, the distance between the HP drivers and the user's ear drums aren't significantly different between different owners, no more than a fraction of an inch or so, rather than potentially a couple of feet or so.

G
Well, as I said right above you, I *don't* like what I'm hearing in this Accord - whether or not ANC is working properly or not. And, since the majority of those Honda and Acura drivers intrepid enough to dismantle half their dash have reported cleaner, louder output with that ANC box unplugged, and no other functionalities(of radio, or car in general) affected, I'd be willing to give disabling a try, although I might have to pay a dealer or someone a fortune just to properly remove and reinstall all that trim & paneling once I've disabled what I want to.

I'm an audio purist, Gregorio, who prefers a minimalist, clean signal path from source to speaker, and could care less about Active Noise Canceling, in theory or practice. My 'noise cancellation' doctrine?...

Maximum insulation, isolation, and amplification power. Not some whiz-bang software solution or gizmo box. Look how that worked out on the Max8-9 737. :wink:
 
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Well, as I said right above you, I *don't* like what I'm hearing in this Accord - whether or not ANC is working properly or not. And, since the majority of those Honda and Acura drivers intrepid enough to dismantle half their dash have reported cleaner, louder output with that ANC box unplugged, and no other functionalities(of radio, or car in general) affected, I'd be willing to give disabling a try, although I might have to pay a dealer or someone a fortune just to properly remove and reinstall all that trim & paneling once I've disabled what I want to.

I'm an audio purist, Gregorio, who prefers a minimalist, clean signal path from source to speaker, and could care less about Active Noise Canceling, in theory or practice. My 'noise cancellation' doctrine?...

Maximum insulation, isolation, and amplification power. Not some whiz-bang software solution or gizmo box. Look how that worked out on the Max8-9 737. :wink:
Comparing ANC to an engineering problem that claimed hundreds of lives? Not the analogy I would have made.

If you're that concerned about ANC, why did you buy a car where it's difficult to defeat? I'd have thought an "audio purist" would have done some basic research to avoid such a problem.
 
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I'm an audio purist, Gregorio ...
Sorry but that doesn't make any sense to me, TheSonicTruth. I'm an audio purist, so I very rarely listen to music in a car (by my choice), because that's by far the least "pure" listening environment I own!

G
 
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Comparing ANC to an engineering problem that claimed hundreds of
lives? Not the analogy I would have made.

If you're that concerned about ANC, why did you buy a car where it's difficult
to defeat? I'd have thought an "audio purist" would have done some basic
research to avoid such a problem.

I know, sorry. Kind of 'Imus' to make such a comparison!

Well, the ANC thing kind of snuck in. When I traded my 2015 Hyundai in for the 2010 Accord, my priorities were handling, a moonroof, steering wheel control of major audio functions as well as cruise, plus - not having to bang my head on the top of door jamb every time I get in the thing! I'm only 5'8" yet still managed to at least brush my head on the jamb of that Elantra everytime I got in. Who knows, along with gimmicky electric steering, maybe the Hyundai employed ANC also. We'll never know.

If I follow the well-published steps to removing center console trim pieces and some dash trim carefully enough, perhaps I could join the ranks of those enjoying the full potential of their Honda and Acura OEM head systems. Aside from that gimmickry, I am more content and satisfied with the Accord that with the Elantra. It's the car I should have bought second-hand five years ago, after my not-my-fault crash.
 
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Sorry but that doesn't make any sense to me, TheSonicTruth. I'm an audio purist,
so I very rarely listen to music in a car (by my choice), because that's by far the
least "pure" listening environment I own!

G
Don't nit pick. Most of us have to make the best of what we got.

Not everyone is endowed with or able to afford an acoustically treated, shock-dampened, time-aligned listening chamber, know what I mean, Greg? :wink::wink:
 
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I'm an audio purist
I'm a music lover. I listen to music in whatever context I can and adapt to the best way to present music in that context. If noise cancellation worked in a car, I'd be interested in trying it. But just from the theoretical standpoint, I can see a lot of differences between noise cancellation in headphones as opposed to in a car.
 
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I'm a music lover. I listen to music in whatever context I can and adapt to the best way to present music in that context. If noise cancellation worked in a car, I'd be interested in trying it. But just from the theoretical standpoint, I can see a lot of differences between noise cancellation in headphones as opposed to in a car.
By "purist" I mean, as clean and clutter free a signal path between the source and my speakers. That includes any electronic noise cancellation gizmotry.

Although, car vs cans, I do agree: implementing ANC in the latter would probably be far easier and be more predictable. (If one insists on having the feature!)
 
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I like whatever presents the music best. Sometimes that is simple and straightforward, sometimes processing can improve sound. My AirPod Pros have fantastic noise cancelling. It's a huge improvement when I'm out and about. And I would be lost without my DSPs for my speaker system. There's no one correct answer. You just have to know how to apply the tools effectively.
 
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I like whatever presents the music best. Sometimes that is simple and straightforward,
sometimes processing can improve sound. My AirPod Pros have fantastic noise cancelling.
It's a huge improvement when I'm out and about. And I would be lost without my DSPs for
my speaker system. There's no one correct answer. You just have to know how to apply the
tools effectively.
DSPs, for which speakers, home/personal or for work?
 
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