Active Noise Cancellation: What is it and How does it works

You would have many times come across claims by headphone companies "this headphone or earphone have active noise cancellation" or by smartphone companies "this phone has dual microphone for active noise cancellation" or even by premium car manufacturers that their car sports active wind and road noise cancellation. Question would arise in your minds that what is this active noise cancellation; here you will find out !!

What is this active noise cancellation ?

Active noise control (ANC), also known as noise cancellation, or active noise reduction (ANR), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. It's based on the principal of superposition of sound waves. It is majorly used in Headphones, Smartphones and Cars, not to mention in Music studios.

Noise cancellation in Headphones and Earphones

Noise-cancelling headphones  are headphones that reduce unwanted ambient sounds  using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing. Noise cancellation makes it possible to listen to music without raising the volume excessively.

Noise-canceling headphones come in either active or passive types. Technically speaking, any type of headphone can provide some passive noise reduction. That's because the materials of the headphones themselves block out some sound waves, especially those at higher frequencies. The best passive noise-canceling headphones, however, are circum-aural types that are specially constructed to maximize noise-filtering properties. That means they are packed with layers of high-density foam or other sound-absorbing material, which makes them heavier than normal headphones. The tradeoff of all that extra weight is a reduction in noise of about 15 to 20 decibels (dB). But considering jet engines create 75 to 80 dB of noise inside the aircraft cabin, passive models have some serious limitations. That's where active noise-canceling headphones come in.

If you look at the illustration , you can see how this works. Notice that the two waves -- the one coming from the noise-canceling headphone and the one associated with the ambient noise -- have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out, a phenomenon known as destructive interference. The result: the listener can focus on the sounds he wants to hear.

Noise Cancellation In Smartphones

The first thing you might not know is that your phone has more than one microphone. In most cases this will be a secondary or tertiary microphone, and will be placed at strategic points around your handset. From here, simple mathematics is used to create an algorithm that works out just what noise is present and how to eradicate it. A primary microphone is aimed to your mouth to record your voice, whilst also picking up any noise from around you. In a single microphone circuit, this comprises all the data that is sent via the air waves to the receiving handset. With a secondary microphone located elsewhere, usually near the top and on the back of the handset (so it doesn't pick up so much speech), a lot of background noise can be removed. One company making strides in noise reduction is Qualcomm. Its Fluence technology is built into a number of its chips. These chips are the same ones that are found within any number of the highest end flagships, whilst also making its way down to even a few budget handsets.

Noise Cancellation in Cars

Active Noise Cancellation (ANC) is designed to dramatically reduce low frequency noise in the interior. The system operates whenever the car is running, regardless of whether the audio system is on or off. There are two microphones in the cabin area. The microphones capture low-end drivetrain frequencies entering the cabin, and send a signal to the Active Noise Cancellation unit. The control unit then creates a precisely timed reverse phase audio signal that is sent to an amplifier, which powers the door speakers and the subwoofer positioned on the rear parcel shelf.

Since the system is designed to cancel low-frequency sound, it doesn’t use any of the audio system's tweeters. The ANC dramatically reduces exterior noise. In the frequency range below 100 hertz, ANC results in an impressive 10 dB reduction in noise level. Harman’s technology involves the use of four in-cabin microphones, along with four strategically placed accelerometers in the chassis and a proprietary processor to create sound that is 180-degrees out of phase with the noise and vibrations entering the vehicle. This essentially cancels out the noise, creating a quiet, still-feeling environment. Harman says that the technology doesn’t interfere with music performance in a negative way. In fact, the resulting quiet is more conducive to satisfying sound quality, says the company.

The concept of implementing active noise cancelling (ANC) for use in cars is not a new one. Bose, which pioneered ANC technology starting in 1986, has been putting its own version of something similar into the cars of those auto makers it partners with since 2012. Late last year, it also announced noise-cancelling technology that could be implemented in cars that didn’t use its in-car audio systems. However, Bose’s technology handles primarily low-frequency noise, such as equipment knocks and engine noise, and the company told us that dealing with higher frequency road noise is a tough nut to crack (though they are very much working on it).

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