How Active Noise Cancellation Works, and Why It Struggles With Voices

Put on a good pair of noise cancelling headphones on a plane and the engine roar simply fades away. It feels like magic. It’s actually clever physics and very fast processing.

Sound against sound

Sound travels as waves of pressure. Tiny microphones on your headphones listen to the noise around you. A chip then creates a matching wave that’s flipped upside down, called an anti noise signal, and plays it through the speakers. When the two meet, they largely cancel out. Engineers call this destructive interference.

Why it works best on hums and drones

ANC is most effective against steady, low frequency sounds such as aircraft engines, air conditioners, generators and traffic rumble. These waves are long and predictable, so the electronics can keep up. Higher pitched, sudden sounds, such as voices, clattering dishes or a baby crying, change too quickly to cancel completely.

Passive isolation does the rest

The physical seal of ear cushions or earbud tips blocks higher frequencies. That’s why a good fit matters so much. Try different ear tip sizes. If the seal is poor, both ANC and bass suffer.

Feedforward, feedback and hybrid ANC

• Feedforward: microphones on the outside hear noise before it reaches you.
• Feedback: microphones inside listen to what actually reaches your ear.
• Hybrid: uses both, and is common in premium models.

Transparency mode

The same microphones can pipe outside sound in, so you can hear announcements or traffic without taking your earbuds out. It’s useful for walking around cities safely.

Health and comfort

Some people feel a slight pressure sensation with strong ANC. That’s normal for some ears. One real health benefit: in noisy places, ANC lets you listen at lower volumes, which protects your hearing.

The bottom line

ANC is brilliant for planes, buses, offices and noisy homes. Don’t expect total silence against voices, and make sure the fit is right before blaming the technology.

Sources

• Bose, How does noise cancelling work?
• SoundGuys, How active noise cancelling works