How Does Active Noise Canceling Work?


  • Active noise canceling works by replicating ambient noises but does so on the opposite wavelength to the one it “hears”.
  • Because the human brain can’t perceive the same noise on the positive and negative wavelength at the same time, it hears nothing.
  • Active noise canceling is great for low frequencies, but hardware and software limitations make it a bad match for high pitch sounds.

I was always skeptical of the lofty promises of noise canceling headphones. My, admittedly limited, knowledge of physics taught me that everything these headphones claim to offer just simply shouldn’t be possible. Eventually, the allure of uninterrupted audio became too much and I took the plunge. I haven’t regretted it since.

But how exactly does this tech work? Why is it generally so expensive and what does the future hold for noise canceling technology? Today we’re going to take a deep look at the magic behind what makes noise canceling technology tick.


Active Vs. Passive Noice Cancelling

What’s the difference?

There are two main types of noise canceling techniques that are widely used. We’ll mainly be focusing on Active noise canceling in this piece, however, you may see the term passive noise canceling thrown around a lot.

Simply put, passive noise canceling is achieved through physical design. By creating a seal from the outside world you are effectively blocking out a large number of outside noises. While most headphones do an ample job of doing this, there are some headphones that have gone through great lengths to provide an effective noise canceling hardware design and have spent many years of research and development doing so.

That said since there’s no real regulation or industry standard as to what “passive noise canceling” really is, unfortunately, it does mean that many lower quality brands try to pass this claim off when it clearly isn’t true. At least not in any meaningful way anyway. For this reason, I always recommend taking some time to look at the actual design and materials of the headphones to see how much thought has really been put into their design.

How can I spot good passive noise canceling?

Below is a perfect example of this in action. While the product description claims to offer a noise canceling design, it’s hard to identify anything that you wouldn’t find on an ordinary pair of headphones. Just take a look at the overall design. We don’t believe in naming and shaming here at Beyond Amplified, however, it’s safe to say these certainly weren’t produced by any of the bigger audio manufacturers.

On the flip side, let’s take a look at Sennheiser’s “Momentum” range of headphones. They tout noise isolation as one of their killer features. If we take a quick look at their offering, we see a pair of beefy ear cups made from premium materials. There’s no denying these are sure to isolate surrounding external noises. This certainly isn’t just an afterthought either, they’ve been designed from the ground up to dampen noises at a hardware design level.


How It Works

The Basics

So with Passive cancellation explained, let’s move on to the real star of the show, active noise cancellation.

Let’s start by explaining what happens in its very basic technical form. Noise canceling works by using a small microphone to listen out for the noises around you. It then uses that information to produce a wave that is the exact opposite of the waveform it hears, thus, canceling the ambient noise out.

But what does all that actually mean?

I want you to imagine a tug of war. On one side we have Team A, the other Team B. Team A gives the rope a gigantic tug, but Team B reacts instantly by tugging in the opposite direction and mimics their exact force. Because of this, the rope goes nowhere.

So let’s put this into an audio form.

Audio travels through the airspace in “waves” and these waves are made from Compression and Rarefactions, or more simply put “Ups” and “Downs”.

So let’s say a noise is made, it causes the sound waves that reach your ear to shoot up high. Your trusty noise canceling headphones hear this noise via the microphone. They react by creating a waveform in the opposite direction at the exact same force and voila! The two waveforms cancel each other out because brain simply cannot process a compression and rarefaction (Up and Down) of the same frequency at the same time. As a result you simply hear “nothing”. Going back to that tug of war analogy, if the rope was pulled in equal force in opposite directions at the same time, it wouldn’t go anywhere, the end result would again be “nothing”.

Still lost? Don’t worry! This video does a great job of explaining exactly how it works in a more visual form.


Discomfort

Mild Comfort Issues

Now that we have the basics down, as you might have guessed, anything involving “tricking” your brain is going to have some kind of side effect. Because waves travel through the air using pressure to propel them towards your ear, by creating a second wavelength to create that noise canceling effect, the headphones are doubling the amount of pressure that’s hitting your ear.

Unfortunately, if you are particularly prone to motion sickness or general queasiness I have bad news. There’s a good chance you may find noise canceling headphones extremely uncomfortable because of this. Many people liken the feeling to that of an airplane cabin during landing. While this is certainly something you can get used to over time, many users will find noise canceling quite disorientated on first use.

Safety

Something else worth stressing is that, while there may be a small level of discomfort for some, noise canceling technology is absolutely safe. There is no risk involved in this technology and in fact, due to the fact it will enable you to listen to music at a lower volume due to lower outside interference, it can even help save your hearing in the long run. The internet is full of false claims about the hazards associated with noise canceling technology, but there is zero substantial evidence to back this. (Source)


Limitations

What can’t noise canceling do?

There are some limitations to bear in mind when it comes to noise canceling. The most apparent being the types of frequencies it can deal with. While they are great at dealing with low frequencies and can cancel out the noise of airplane engine with ease, they may struggle with the shrieking child sat next to you, I’m afraid.

The reason for this goes back to the “waves” we talked about earlier. Lower frequencies generally have much longer “Ups” and “Downs” in a wave, giving the software and hardware inside your headphones time to catch up.

High frequencies, however, are much shorter and erratic. Human conversation, for example, has a much higher pitch with unpredictable stopping and pausing. Because of this, the device processing all this information would need to work extremely hard to match all these waves. 

Powering the noise cancelation

Another thing to consider is that the processing involved needs to be powered in some form. Whether that’s with a rechargeable internal battery or simply a single AAA battery. While some headphones can function without noise canceling when the battery is dead, not all work this way and some may become completely unusable after the battery is depleted. Something to bear in mind while purchasing.

The good news is that this technology doesn’t put too much of a drain on the battery. Generally, you’re looking at anywhere between 10-30 hours depending on whether the headphones are also wireless or not.

Difference in quality

Something else worth considering when purchasing is that because you are essentially relying on a miniature computer to predict and cancel out the waves, the quality of the processing units can vary greatly. You’ll more or less be getting what you pay for here so if you want true top end noise cancelling, don’t be surprised if you’re asked to fork out anywhere upward of $200 for the full effect the same way you wouldn’t expect a $100 notebook to match that of a $1000 gaming PC. 

One last consideration is that many will also argue that by adding in this extra processing, you’re slowly detracting from the “pure” audio source. It’s unlikely anyone but a true audiophile would really notice the difference here, however, this could be something that becomes more prominent as cheaper manufacturers jump on board with noise canceling technology. This is always one of those things that will be up for debate, but the layman is highly unlikely to truly notice any difference with daily usage.


Summary 

Active noise canceling is an incredibly simple concept when stripped back to basics. We’re essentially tricking our brain into hearing two waves at once in the opposite direction, as a result causing us to hear “nothing”.

Manufacturers are certainly aware of the limitations involved with noise canceling technology in its current form so it’s no surprise they’re mostly marketed towards frequent flyers or those who want to block out their daily commute with the drone of an underground train carriage. They also have a number of practical industrial usages too. For example, those working in ground handling at the airport can combine them with a microphone to effectively communicate with each other without the roar of jet engines in the background ruining their hearing. 

As technology evolves, no doubt noise canceling will continue to impress. At this stage, we have the science down, it’s simply a matter of creating software and processing units cable of predicting and handling those higher frequencies more effectively. Consider how smartphones and tablets have evolved in recent years and the mass market appeal of blocking out the droning noises of the outside world, the future of noise canceling technology looks to be very bright indeed.