Active noise-canceling (ANC) headphones are not magic walls that remove every sound. They use the fact that sound moves as waves and that two waves can affect each other.
A microphone first listens to the noise around you. A small processor then analyzes that signal and calculates a response. The headphone’s speaker creates another wave with an opposite pressure pattern.
When the two waves reach your ear at nearly the same time, they overlap. A high-pressure part of one wave meets a low-pressure part of the other, so the total change becomes smaller. This is called destructive interference, and it reduces the noise you hear.
Steady sounds are easier to predict than sudden or rapidly changing sounds. This is why active noise cancellation often works well against the low, steady hum of an airplane engine or a train. Speech, clapping, and sudden traffic sounds change faster, so they are harder to reduce.
Headphones do not depend on electronics alone. Cushions or ear tips physically block some outside sound; this is passive isolation. Many products combine passive isolation with active cancellation.
Noise canceling, therefore, does not create complete silence. It reduces certain sounds and can make music or speech easier to hear without raising the volume. Users still need to consider listening volume and remain aware of their surroundings.