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zap_p25 t1_j2dhon3 wrote

There are two forms of noise cancellation. Active and passive. Passive essentially means just blocking sounds from getting by such as how over the ear hearing protection works. Active uses electronics and math. The active method is fairly simple to explain though may be more ELI 17 due to geometry and sinusoidal waves. A microphone picks up the ambient noise, and reproduces it in the speaker 180° out of phase which in turn nulls the sum of the noise’s amplitude. The out of phase thing, just means there is an ever so slight delay (which is dependent on the frequency).

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MyMomSaysIAmCool t1_j2do65k wrote

There's a third kind that's used for gun hearing protection. Shooters earmuffs use passive noise cancellation, but also have external microphones and internal speakers. When you wear them, the microphones transmit sound to your ears. But they will not transmit any loud noises such as gunshots.

The result is that they give you super sensitive hearing. But there's no risk of hearing damage, because if the electronics fail or the battery goes dead, you're left with passive noise cancellation.

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zap_p25 t1_j2dqx8y wrote

Those are a bit different. They don’t use active noise cancellation. They just use the limits of the audio amplification circuitry. Essentially sounds above a certain threshold just don’t get amplified and the passive noise reduction does it’s thing.

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