19/10/2019 11:11 AM IST | Updated 19/10/2019 11:12 AM IST

What Are ANC Headphones, How Does Active Noise Cancellation Work, Which Ones Should You Buy?

Active and Passive noise cancellation, sound cancellation or isolation, there’s a lot that you need to consider when buying sound cancelling headphones. Here’s what you need.

Mention headphones or earphones, and active and passive noise cancellation will pop up at some stage of the discussion. You want to make sure that you get a clear audio experience, with minimal outside interference. No one wants disturbances if they can avoid them, and if you’re traveling while you listen to your favourite playlist or podcast, getting a noise-free experience can be difficult.

All earphones or headphones attempt to keep noise out, either by covering your ears with thick cups (or cans) or by having ear plugs that go really deep inside your ear. Noise cancellation takes things one step further, in order to let you focus only on what’s playing on your headphones.  This is done in two ways.  

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Active noise cancellation - when two sound waves collide, and silence ensues

The more high-profile of the two is active noise cancellation, or ANC as it is called by many people. The reason it gets so much attention is because well, it is technologically rather sophisticated. In simple terms, ANC is a system that actually produces waves that” kill” the external sound.

Headphones with active noise cancellation come with microphones that are meant not for talking or taking calls, but which measure the  sound around you (“ambient sound” or “noise”) and produce waves to cancel it out.

So when you are using headphones with active noise cancellation, the microphones in the headphones hear a wave of sound from outside (sound . They then produce a wave of their own that will cancel out the incoming wave. These two waves cancel each other out, and let you have a clear, uninterrupted audio experience. It is almost like a battle between good sound (the one you want to hear) and bad sound (the noise coming from outside), with the good sound winning, if things go well. 

When it works perfectly, ANC can enable you to sit in a crowded, noisy room and still hear nothing but what is playing on your headphones. In essence, it eliminates external sound. And while it is not always 100% successful, it certainly makes a massive difference to your audio experience. 

Of course, not all ANC headphones are alike. A lot depends on the quality and placement of microphones in the headphones themselves, and the technology used in producing the waves that are supposed to eliminate noise. So the level of external sound that gets cancelled by say, a Bose 700 (that costs more than Rs 30,000) is likely to be far more than from a device that costs about Rs 5,000—the Bose device even gives you different levels of ANC, depending on your requirements.

Bose acoustic noise cancelling headphones are shown Thursday, August 17, 2006 in New York. (AP Photo/Mark Lennihan)

Inefficient or badly implemented ANC can even inhibit the audio experience, with the waves being emitted by the headphones being heard even by the user, sometimes in the form of a light clicking sound or a slight buzz. Those additional microphones for ANC and the process involved in generating waves to counter noise also guzzles power—so if you are using wireless headphones, turning on ANC will reduce battery life, and even if you are using wired headphones, well you will have to keep a separate battery unit charged to be able to use ANC. 

Also for all its utility, ANC can be a bit of a two-edged sword. Yes, it allows you to focus almost totally on what’s playing on your headphones, but there are times when you need to listen to ambient sound. For instance, while crossing a road or while going out for a run—you might not love the sound of traffic or people calling out, but ignoring them altogether could have dangerous consequences. That noise might be annoying but it could save you a limb. Or a life. 

Passive noise cancellation/ noise isolation — seal the noise out

You do not have to get into complex wave production (and relatively high expense) to keep external sounds out from your headphones. If you are just looking for a reasonably good hearing experience, and are on a slightly tighter budget, well, then you could try for headphones that cancel noise passively.

Not by producing sound, but by simply keeping it out, and placing a sort of physical barrier between your ear and external sounds. This process of keeping noise at bay is called passive noise cancellation or noise isolation—unlike ANC, it does not have a geeky abbreviation, but it remains effective nevertheless. 

Every headphone has some sort of passive noise isolation. In fact, you yourself are creating passive noise isolation when you do something as simple as covering your ears with your hands. Unlike active noise cancellation which involves a mechanical process (microphones measuring sound and generating waves to cancel them out), passive noise cancellation is simply about keeping the noise out, and is more about the design of the headphones.

You can get decent sound even without ANC or good noise isolation—this just keeps the noise out.

The amount of noise that will be kept out depends on how well the headphones fit into and cover the ears of the user, the extent of the padding (if any) used, and the materials themselves used in the headphones. As a general rule, the thicker the padding around the headphones, or the more snugly (and deeply) earphones or buds go into your ears, the more noise gets kept out and the better is your listening experience.

It cannot kill noise as effectively or as precisely as ANC does, but noise isolation is a whole lot more affordable and needs no battery to operate on. And unless you have really heavily padded headphones or deep-set earplugs, ambient noise will not be totally kept out. So yes, you will hear traffic sounds and if someone calls out, you will hear them too.

A number of audio purists also prefer listening to sound on noise isolation headphones as the sound is considered to be more “pure” and not affected by any software quirks.  ANC headphones might make news but you will seldom see them being used in recording studios by “audio professionals.” That said, noise isolating headphones can tend to be bulky and uncomfortable as they try to seal off your ear from external sounds. 

So which one do you need?

So which kind of headphones do you need? ANC ones or the ones that handle noise passively? Well, it really depends on the circumstances in which you mostly use your headphones. ANC headphones are perfect for those who need to focus on sound but are often in very noisy conditions.

They are great for listening while on a flight or in a crowded place. However, if you are a more “casual” listener and do not mind external noise as much, then ANC might not really be worth the additional dent it would make on your wallet. For, all things remaining the same, a pair of headphones with ANC will be significantly more expensive than those without it. 

Just remember that neither has anything to do with actual sound quality. You can get decent sound even without ANC or good noise isolation—the Apple AirPods do not have ANC and are not the greatest in keeping external sound out either.

It is all a matter of noise, really. Go for ANC, if you want it totally out of your listening experience. And are willing to pay a premium for it.

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