What’s the Difference Between Active and Passive Noise Cancellation?

Active sound-enhancing headphones and earbuds have skyrocketed in popularity over the past few decades, spreading from a niche product popular among frequent flyers to a near-ubiquitous technology. Whether we’re talking about Apple’s ubiquitous AirPods Pro or high-end headphones from brands like Sony and Bose, it seems there’s one thing we can all agree on in these divisive times: the world around us is loud and we don’t want to hear it.

But if you’ve spent time looking for the best noise-cancelling headphones, you may have come across a confusing difference between passive and active noise reduction. At a basic level, the difference between the two is that noise canceling (ANC) headphones use a computer algorithm to prevent you from hearing outside sounds, while artificial noise cancellation uses physical materials. But the human ear is a remarkably sensitive instrument, and keeping it from doing its job is not easy. The limitations of both types of mitigation are large enough that they both work best when used in tandem.

But the details of this technology get very interesting. To work, active noise cancellation uses the polarity of sound to create something called anti-noise, which destroys sound before it reaches your eardrum. And active noise cancellation is so central to how most gaming devices work that allowing ambient noise to pass through requires more engineering work. Here’s what you need to know about both types of noise cancellation.

Active noise cancellation is the easiest type to understand. It simply means using material to block sound from reaching your ears. If you put your hands over your ears, that’s noise cancellation. Ditto for wearing earmuffs or earplugs. In the context of headphones and earbuds, passive noise cancellation is what happens when you put your headphones on without opening them.

Almost all pairs of earbuds or headphones have noise cancellation by definition, because you cover your ears in the case of headphones or fill your ear in the case of earbuds. Wearable audio playback devices that don’t quietly isolate the listener are rare, and they’re designed for that functionality. For example, many musicians and audiophiles want open back headphones, with open earcups to allow for more natural sound in a studio or Hi-Fi listening environment. Recently, open-ear earbuds have also seen a rise in popularity among outdoor sports and fitness enthusiasts. Exemplified by products such as the Shokz OpenDots 2, these usually attach to the outside of the ear and the sound of fire enters it while leaving the canal unobstructed so that workers can hear someone talking to them, or so that runners and cyclists can navigate urban areas without being disturbed by a passing SUV.

Importantly, passive and active noise cancellation work together. Noise-cancelling headphones often require the listener to make sure the earcup pads make a noise-canceling signal in their ears. Some people who wear glasses will find that some noise-canceling headphones don’t work well for them because the arms of their glasses prevent the formation of a blockage in the ears.

With active noise cancellation, or ANC, your earbuds or headphones are equipped with a small, internal computer that uses an algorithm to cancel noise. The term is important. Although the noise cancellation is done physically blocks That’s right, the ANC is doing it cancel it. Microphones on the outside of the gaming device analyze the surroundings of the wearer. The computer then creates something called anti-noise, an out-of-phase version of outside noise. It’s like adding a negative number to the positive number and you get zero. When outside noise mixes with counter-noise, they literally cancel each other out, destroying the existing sound before it even hits your eardrums.

But the ANC has severe limitations as we write. To create the perfect noise-cancelling sound, your ANC headphones must accurately capture real sound. Many companies have solved this by throwing an increasing number of microphones into the problem. The Sony WH-1000XM6 headphones released earlier this year have a 12-microphone array. But still, these pinhole microphones are limited. In addition, the ANC processor will always lag, reacting to the noise rather than keeping up with it. This is why ANC works best when it cuts out constant, low sounds like the air conditioner, and why you might hear things like cafe chatter.

Because of those limitations, passive noise cancellation is the first line of defense in ANC headphones. The more noise you can block from the listener’s ears, the less noise you need to use the ANC processor. That’s why even the best noise-cancelling earbuds can’t reduce to the same level as competing headphones – sticking something in your ear doesn’t quietly block out as much noise as shutting them off completely.