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Noise cancellation
Intermediate
Anti-phase sound cancels unwanted noise.
A microphone samples noise and a speaker emits the same waveform with opposite phase, so the sum cancels. It works best for steady low-frequency sound such as engine hum.
Aeroplane headphones.
Needs precise phase matching.
In more detail
Active noise cancellation uses a microphone to detect unwanted sound and a speaker to emit an equal, opposite wave. Superposition then cancels the noise, mostly at low frequencies.
Real-world uses
- Headphones use active cancellation on flights and commutes.
- Industrial machinery uses cancellation to reduce noise in workplaces.
- Car manufacturers use anti-noise systems to cancel engine hum inside the cabin by playing an inverted version of the noise.
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Frequently asked questions
Why does it work better at low frequencies?
Long wavelengths are easier to match in phase and timing than short ones.
Can it remove all sound?
No. High frequencies and sudden noises are harder to cancel completely.
Can noise cancellation remove all sound?
It works best for steady, low-frequency noise. Sudden or high-frequency sounds are harder to cancel completely.