What's the difference between active noise canceling and passive?

Active noise canceling headphones and earbuds have skyrocketed in popularity over the past couple of decades, spreading from a niche product popular among frequent fliers to a nearly ubiquitous technology. Whether we're talking about Apple's ubiquitous AirPods Pro or premium consumer headphones from brands like Sony and Bose, it seems like there's one thing upon which we can all agree in these divisive times: the world around us is way too noisy and we'd rather not hear it.

But if you've spent time looking at the best noise-canceling headphones, you've likely come across a puzzling distinction between passive and active sound attenuation. At a basic level, the difference between the two is that active noise canceling (ANC) headphones use a computer algorithm to prevent you from hearing outside noises, while passive noise canceling uses physical objects. But the human ear is a remarkably sensitive instrument, and keeping it from doing its job isn't easy. The limitations of both attenuation types are large enough that the two work best when deployed in tandem.

But the details of these technologies get far more interesting. To function, active noise canceling uses the polarity of sound to create something called anti-noise, which physically destroys sound before it can reach your eardrum. And passive noise canceling is so core to the way most playback devices operate that allowing ambient noise through requires additional engineering work. Here's what you need to know about both forms of noise canceling.