Active noise cancelling (ANC, aka active noise control) is a set of audio technologies which actively cancel the ambient noise.
Both the annoying noise and music reach your ear as sound waves transmitted through the air.
So, one simple way to reduce noise is to physically and passively block it. For example, there are many soundproofing materials and technologies.
In the airport, you may notice ground staffs are wearing ear muffs to block the engine and other noises In shooting club, it is also common that ear muffs are used.
Active noise cancelling (ANC), on the contrary, uses negative sound waves to actively cancel the noise.
This means ANC requires at least three components:
- Power source. Active noise cancelling (ANC) always requires a power source to detect and analysis noise and then generate a negative wave.
- Noise detection. Normally, one or more microphones are used to sample the ambient sound.
- Anti-noise sound wave generator. Once the ambient noise is sampled, active noise cancelling (ANC) system must generate an inverted (negative) sound wave (with similar amplitude) to cancel the low-frequency noise.
When the ambient noise is cancelled, you will get a quieter environment for your music.
Active noise cancelling (ANC) is still evolving, especially on how to sample ambient sound, how to analyse the sampled ambient sound, and how to effectively cancel the low-frequency ambient noise.
Please note, active noise cancelling (ANC) currently is most effective for low-frequency noise only.
Active noise cancelling (ANC) vs passive noise blocking
As discussed earlier, noise can be “blocked” (passive) and/or “cancelled” (active).
Most headphones, in-ear or on-ear or over-ear, can block certain ambient sound. For example, some in-ear headphones are designed to seal the ambient sound. Of course, over-ear headphones usually can block more ambient sound.
For headphones, some manufacturers may also refer noise blocking as noise isolation.
Anyway, the differences between active noise cancelling (ANC) and passive noise blocking (or noise isolation) are obvious:
- Active noise cancelling (ANC) cancels ambient noise selectively. Although different manufacturers may use different algorithms and technologies, they all try to mainly cancel the low-frequency ambient noise. While noise blocking or noise isolation will always block all frequencies.
- Active noise cancelling (ANC) requires a power source. To cancel the ambient low-frequency noise, the control unit in noise cancelling headphones must generate sound waves. Of course, power source is also used to analyse the sampled ambient sound. While noise blocking (noise isolation) relies on physical barriers made by noise-isolating and absorbing materials.
- Active noise cancelling (ANC) can be complimented by passive noise blocking (isolation). All headphones have certain capacity of blocking ambient noise. Most noise cancelling headphone manufactures also try to improve the physical blocking or isolation of ambient sound as well.
Anyway, if you need a headphone with noise cancelling, you should not be fooled by noise isolation claimed by a few manufactures.
In addition, a lot of Bluetooth headphones may also claim the noise cancelling feature. However, such noise cancelling usually refers to microphone input, not ANC. You should not be misled by such claims/features.
How active noise cancelling headphone works?
As mentioned, in any headphones with ANC, there is at least one (usually 2) microphones dedicated for ambient sound sampling.
These sampling microphones normally were positioned outside of the headphone. For example, for over-ear headphones with ANC, the sampling microphones are usually in the outside of the cap (for example, Bose 25). It is possible to put such microphones inside the cap. Theoretically, this sounds better. But in the reality it is a bit complicated because the music is also pushed to the same region.
The ambient sound is continuously sampled. The sampled sound waves were processed in the ANC unit in real-time. The delay usually should be in the order of milliseconds.
This ANC unit is the brain for noise cancelling. Different vendors may use quite different technologies and algorithms to generate the negative sound wave based on the sampled ambient noise.
The generated sound was then superimposed on your music. So, when the sound wave reaches your ear, the ambient noise is effectively cancelled. Most branded noise cancelling headphones currently can reduced the ambient low-frequency noise up to 80-95%.
Do you know what active noise cancelling (ANC) is and how ANC works in headphones?
If you have any questions on active noise cancelling (ANC), or if you have any questions on headphones with ANC, please let us know in the comment box below.
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