Guide · Headphones
Noise cancelling, explained without the marketing
What active cancellation actually removes, what it cannot touch, and which number on the box is worth reading.
Active noise cancellation works by playing the inverse of the sound reaching a microphone. That is easy for steady, low-frequency noise — an aircraft cabin, a train, a fan — and hard for anything sudden or high-pitched, which is why a colleague’s voice cuts through a jet engine that the headphones erase entirely.
The practical consequence is that “dB of cancellation” on a box tells you very little without a frequency. A pair that removes 30 dB at 100 Hz and 6 dB at 2 kHz is a great flight headphone and a mediocre office one.
Passive isolation — the seal of the earcup — does the work that cancellation cannot. It is also the part that degrades: pads harden, the seal breaks, and performance falls long before the battery does. Budget for a pad replacement in year three.
Which is why our headphone comparison leads with battery, weight and codec support rather than a cancellation score. Those numbers are published, checkable and comparable — and where a figure comes with a condition attached, such as a battery life that only holds on one codec, we put the condition next to it. A single decibel figure is none of those things.