Active vs Passive Noise Cancelling

Active and passive noise-canceling both sound like some futuristic technologies, but one of them is just masquerading its complexity. Here is a guide.

Answer:

Active noise canceling makes use of microphones to analyze ambient noise and counter it by electronically generating mirror images of said ambient noise.

Passive noise canceling is what you get when you stick your fingers in your ears – it’s a physical obstruction that may or may not prevent some sounds from reaching your eardrums.

It doesn’t take a lot of guesswork to figure out what the main benefit of noise-canceling headphones is – it’s right there in the name.

But while more and more manufacturers are marketing their headphones as noise canceling, the methods they use to reach this desired effect can vary hugely.

In broad strokes, we can separate noise-canceling devices into those that utilize active noise canceling (ANC) and those that utilize passive noise canceling (or noise isolation).

ANC and noise isolation have next to nothing in common and carry different benefits and drawbacks, so it’s important to understand which one better suits your needs before committing to either one.

Active Noise Cancelling vs Passive Noise Cancelling

To illustrate the difference between these two approaches to noise-canceling, we’re going to have to get medieval for a second.

First up, imagine a castle. The castle has high walls that were made to repel invaders. They are a form of obstruction. Even if the castle walls were unmanned, if the gates are closed, we couldn’t just waltz in. The walls are enough to stop us dead in our tracks.

But we’re clever people (and really motivated to get inside those walls for some reason), so we bring a giant ladder. Now, if the walls are unmanned, we could get in. However, if the walls were protected by guards, our chances of breaking in would fall drastically as the guards would employ active measures to stop us.

This situation is strangely similar to the way noise canceling works if we imagine the assaulting forces as sound, the walls as ear cups, and the area on the other side of the wall as our ears. Ambient noises are constantly trying to find their way inside our eardrums. But they have a hard time passing through physical obstacles.

Some physical obstacles present a larger hurdle than others, but all of them are a hurdle. For example, we often can’t hear what people are doing in adjacent rooms unless they’re being very noisy – the walls block out those sounds. This is what’s known as noise isolation.

And this is what some manufacturers are trying to pass off as passive noise canceling as if it’s some fancy feature. It does work though – anyone who’s ever plugged their ears with their fingers to drown out surrounding noise can testify to that.

On the other hand, active noise canceling actually works to eliminate ambient sounds by utilizing some impressive technologies. To explain how ANC works, it will help to learn how the idea behind ANC was first conceived.

How ANC Was Invented

Back in 1978, Dr. Amar Bose (the Bose) took a flight from Zurich to Boston and absolutely hated how the noise of the airplane drowned out the music he was listening to on his headphones. So, being a super smart guy, we decided to take it upon himself to bestow the world a solution to this problem.

His solution – headphones that could listen in on the ambient noise and eliminate it using destructive interference. It took him eight years to build the first working prototype, but it wasn’t long before airlines and the military realized he’d struck gold. That is to say, the technology has been here for a while and it has a solid foundation, even though it’s only entered the mainstream relatively recently.

To this day, Bose is a leader in the field of active noise canceling, although other companies have got a good handle on the technology by now as well, particularly Sony, who’s on par with Bose when it comes to producing high-quality ANC headphones. So if you’re going to buy such a device, you can’t go wrong with Sony or Bose.

But first, let’s see whether or not this is something worth buying for the average consumer by looking at the benefits that noise canceling brings to the table.

The Benefits of Noise Cancelling

Naturally, the main appeal of noise-canceling is being able to listen to your music (or whatever else it is you’re listening to) without any disruptions. And not just because this will elevate the listening experience to new heights or let you completely immerse yourself, although these are good reasons.

The best reason for purchasing a pair of headphones with good noise canceling is because it promotes safer and healthier listening and can therefore prevent hearing loss. The threat of noise-induced hearing loss is very real. We cover this topic in-depth in this article, but to generalize it, you shouldn’t listen to music at volumes over 60% if you want to maintain good hearing.

In a vacuum (literally and figuratively) this isn’t a problem if you’re using good quality headphones. So why do we listen to music at louder volumes?

The main two reasons are these:

  1. We try to drown out ambient noise. If at 60% volume you can still hear what’s happening around you, you turn the music up so that it will overpower the ambient noise. This is why noise canceling is so helpful.
  2. Low-quality headphones often won’t be able to reproduce music the way it should be, so we turn up the volume to better hear certain frequencies that the driver has a problem delivering. Admittedly, this doesn’t have anything to do with the topic of this article, but it’s good to know that there’s such a compelling reason for casual consumers not to buy low-quality products just because they’re not audiophiles.

ANC – How it Works, the Pros and the Cons

So, how exactly do ANC headphones work?

As we’ve mentioned, these headphones feature miniature microphones that actively listen in on and analyze ambient sound (with sound, of course, being a wave constructed through vibrations). Like all waves, sound waves have peaks (+) and valleys (-). Math tells us that positive and negative numbers cancel each other out if their total sum equals zero. This same principle is used by balanced audio connections to eliminate interference.

So after the microphone analyses the surrounding ambient noise, the headphones generate antiphases – sound waves that are exact opposites of the ambient noise. Both the ambient noise and antiphases make their way inside your ear together and, ideally, cancel each other out completely, leaving only the sound you want to hear. This is known as destructive interference.

We say ideally because ANC technology isn’t flawless, despite the math behind it being sound.

For starters, the antiphases generated by the headphones aren’t perfect opposites of the ambient sound. If the highest peak of an ambient sound wave is 10, the antiphase generated by the headphones would have to be at -10 to result in perfect silence. More often than not, the antiphase will generate a -8 or a -6. This will still result in less noise, but not in perfect silence.

Furthermore, ANC handles certain frequencies better than others. In particular, it has a much better time reducing low-frequency noises than higher ones. Between the microphone registering the ambient noises and the headphones analyzing them, there’s very little time to construct antiphases. And it just so happens that low frequencies take less effort to cancel out.

This is why ANC headphones will have no problem reducing the low and steady vroom of a car engine, but won’t manage to catch the high and sudden honk of a car horn. Of course, sudden and erratic sounds are also a sore point of ANC in general. If, in a fit of road rage, a driver holds down the horn for a long time, good ANC headphones may well catch on and reduce the noise despite the high frequency. But if the noise is instantaneous, they just won’t react as well.

That said, some subtypes of ANC are a bit better at this.

Types of ANC Technologies

There are three subtypes of active noise canceling: feedforward, feedback, and hybrid.

They differ in terms of microphone placement, which affects their ability to self-correct and the time they have to generate antiphases. We won’t go too in-depth about the differences of these ANC technology subtypes in this video, but the short of it is this:

  • Feedforward ANC is better at canceling higher-frequency noises, but it has no means of self-correcting, so in worst-case scenarios, it can even amplify certain sounds.
  • Feedback ANC lets the microphone hear the anti-noise it makes, but because the microphone is closer to the ear, it has less time to react and is therefore not as effective at canceling our higher frequency noises.
  • Hybrid ANC employs both previously mentioned methods, with microphones inside and outside the earcup. This lets it reap all the benefits without suffering any of the drawbacks. It also costs as much to make as the two other subtypes combined.

Obviously, it takes the best of the best ANC has to offer to cancel out the annoying highs of crying babies on airplanes, but it can be done. It’s not cheap, but a Sony WH-1000XM4 will have no problem doing this. Hopefully, understanding the breadth of the differences in ANC subtypes will underpin the point that not everything that has ANC (or worse yet noise-canceling) plastered on the box can be expected to perform phenomenally.

Downsides of ANC

Now if you are already considering dropping massive amounts of cash into a pair of ANC headphones, you should know what downsides they come with (aside from the price, of course).

One of the biggest downsides of using ANC is the fact that using it brings down the overall audio quality of the headphones. After all, the headphones need to generate their own antiphases as they’re playing your music, which is too taxing for even the best ANC headphones to do without any sound degradation – even though you ideally won’t hear the antiphases, the drivers will have to generate them while also playing your music.

This downside is usually offset by the fact that being able to hear music without any ambient noise will enhance the listening experience. Thankfully, most ANC headphones let you turn this feature on and off at your leisure so that you don’t have to suffer the lower audio quality when you’re already in a quiet environment.

Another downside is the pressure that using ANC puts on your ears. To put it simply, wearing headphones with the ANC turned on will make you feel like you’re going through a tunnel. This isn’t in any way physically painful, nor is it harmful, but it can get irksome.

Also, there’s just the general fact that there’s no way to tell how well the ANC is implemented in a particular pair of headphones without using them. Looking at the specs tells you nothing whatsoever about the quality of the ANC featured in that product.

What’s particularly irritating is that you’ll often see or hear claims like 10dB of noise-canceling, but for that, you’d need ANC that’s equally good at creating antiphases for all sound frequencies, and that just doesn’t happen.

In fact, if you want to reduce ambient mids and highs, headphones with good passive noise isolation will often work better than your average ANC headphones.

This is why we recommended choosing a pair of headphones made by a reputable company with a proven track record. Of course, looking at reviews can also help if you’re not into Bose and Sony products or you simply want a quality pair of budget ANC headphones. They do exist, believe it or not; in fact, we’ve featured some in our best noise-canceling headphones guide.

Passive Noise Cancelling

We’ve already explained all these is to know about how passive noise cancelling works, but we’d also like to use this opportunity to talk about some of its pros and cons.

Headphones that have excellent passive noise cancellation are constructed in a way that impedes ambient sound waves from reaching your ears – this means thicker and denser materials. For example, leather ear cushions do a better job of isolating sound than mesh ear cushions. You should not underestimate how effective this can be.

Just imagine this scenario: It’s raining. You’re wearing a hood to keep your head dry. Walking side by side with you is a friend trying to hold a conversation. You may have trouble understanding them just because of the noise isolation the hoodie provides. So when manufacturers set their mind to maximizing noise isolation, they can achieve masterful results.

Construction workers use thick earmuffs that are designed to maximize noise isolation.

The upside of passive noise canceling is that it’s cheaper. It also doesn’t impede audio quality and it can even outperform poor quality ANC, especially when it comes to blocking out the mids and highs. But the downside is that the threshold of loudness that they can block out is lower than that of ANC. And it’s predicated on the device forming a proper seal around your ears or inside your ear canal.

Getting a good seal is imperative in order to achieve passive noise isolation. This is why earbuds don’t sound good if you’re not using the best ear tips for your ears. But we all have different ears, and we don’t just mean the ear canals. This is why even regular on-ear or over-ear headphones can create a better seal for some people than for others, resulting in more or less noise isolation.

Which is Better For You?

Due to the way in which noise canceling promotes healthier listening habits, we feel that everyone should bear this feature in mind when shopping for headphones.

But which type should you get?

  • Active noise canceling is a sophisticated technology that works to eliminate noise, but due to technological limitations, it does its best work while canceling low-frequency noises and gradually gets sloppier as the ambient noise rises in frequency.
  • Passive noise-canceling (or noise isolation) uses dense materials as a physical obstruction to prevent ambient noise from reaching your ear. Overall, it doesn’t fare as well against loud volumes, but it is more effective at drowning out the mids and highs than most ANC.

ANC headphones are indispensable for folks who travel a lot and people who work in noisy environments. It’s a cool feature, but not everyone needs it.

Pound for pound, though, passive noise-canceling headphones tend to have better audio quality, so if you don’t find yourself in a lot of noisy environments you can save a few bucks and get better audio without sacrificing anything.

If you can identify which types of noises bother you the most, this should help you pick the method of noise-canceling that’s more effective for you.

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James is a self-proclaimed audiophile and tech geek. With his CS degree, 5 years of experience as a software developer and 2 years of experience testing audio devices, James is more than fit to be trusted in this field.