ANC headsets aren’t all the same: The three types of ANC

By suki.wang@dgbosta.com   June 5, 2019

Active noise cancellation (ANC) has becomea popular feature in music headsets. Many headsets now boast ANC, but not allof them are created equal. Let’s see why.

As I have briefly mentioned in an earlierpost, ANC is all about generating “anti-noise” that mirrors and cancels theambient noise. (The technical term for this is “destructive interference,”which makes ANC sound like a bit of a badass fighting for the good guys.)

In an ideal world, ANC should result in acompletely noise-free experience for the one wearing the headset. Spoileralert: We don’t live in an ideal world.

Active noise cancellation isn’t a brand newconcept – it actually goes way back to the 1930s:

1934: German inventor Paul Lueg registers atheoretical patent for cancelling noise by using interference and creating“zones of quiet.”

1950s: Harry Olsen demonstrates how ANC canbe used in practice for e.g. reducing noise in passenger vehicles.

1986: Dick Rutan and Jeana Yeager flyaround the world using ANC headsets from Bose to reduce airplane noise.

1990s: ANC headsets see widespread use inthe military and civil aviation.

2000: Bose launches the first consumer ANCheadset.

Since then, lots of music headsets withactive noise cancellation have hit the market. They all claim to cancellow-frequency noise. But getting active noise cancellation to work well isabout more than just throwing some ready-made tech inside the headset andslapping “ANC” on the packaging. There are many other things that make a greatANC headset.

What makes a great ANC headset?

Not all ANC headsets sound equally well.Here’s a good video that illustrates this:

Why does this happen? The short version isthat there are different types of active noise cancellation and that headsetdesign itself plays a big role. Let’s dig a bit deeper:

The three types of active noise cancellation

While the basic ANC concept is the same, itcan be implemented in three different ways: feedforward, feedback, and hybrid.Each approach has its good and bad sides.

Feedforward active noise cancellation (Micoutside the ear cup)

In a feedforward setup, the microphone isplaced outside the ear cup. The mic hears the noise before the person does. ANCthen processes the noise and creates the anti-noise before sending theresulting signal to the headset speaker

Why it’s good:

The mic picks up the noise early on, so ithas more time to respond and generate the anti-noise. This also means that it’sbetter at reducing higher-frequency noise up to 1–2 kHz.

Why it’s not so good:

This setup has no way to self-correct,since it never hears the anti-noise it makes. It just assumes the listenerwon’t hear any noise and goes, “Welp, my job here is done.” If the personplaces the headset incorrectly or if the noise is coming in at a weird angle,this setup can accidentally end up amplifying the noise at some frequencies.Oops!

On top of that, feedforward ANC workswithin a narrower range of frequencies. So, if you focus on reducing noise ataround 1 kHz, feedforward ANC may end up having little effect at lowerfrequencies. And because the mic is closer to the outside world, it’s moresensitive to wind noise.

Feedback active noise cancellation (Mic inside the earcup)

In the feedback setup, the mic lives insidethe ear cup and in front of the speaker, so it gets to hear the resultingsignal in exactly the same way the listener does.

Why it’s good:

Because it hears what the person hears,feedback ANC can better adapt to variations and correct the signal if needed.Feedback ANC also works on a broader range of frequencies. Another advantage isthat even if the headset is worn in an odd way or doesn’t quite cover the ears,feedback ANC can account for this, at least to some extent.

Why it’s not so good:

It can’t deal as well with higher-frequencysounds, so it’s not as effective as feedforward ANC at suppressing noise in the1–2 kHz range. If designed incorrectly, there’s also a risk of feedback noise –you know, the painful, high-pitched shrill you get when you place a microphonetoo close to a loudspeaker.

Similarly, designers need to account forthe fact that feedback ANC treats incoming music along with the noise. If theydon’t, ANC can accidentally filter out that sweet, low-frequency bass line ofyour favorite songs. Oops!

Hybrid active noise cancellation (Mics outside andinside the ear cup)

As you can guess, a hybrid approach takesthe best of both worlds, combining feed forward and feedback ANC by placing amicrophone on the inside and outside of the ear cup.

Why it’s good:

You get all of the benefits with almostnone of the drawbacks. Hybrid ANC can suppress noise at a broader range offrequencies, adapt to and correct errors, and is not as sensitive to how theperson wears the headset.

Why it’s not so good:

Because it uses both approaches and twomicrophones, hybrid ANC tech costs – say it with me – twice as much. It alsorequires more expertise to get just right. Having two microphones can generatemore unwanted “white noise,” so higher-quality microphones are needed tocounteract this. As a result, headsets with hybrid ANC will be more expensiveoverall.

So, then – making a great ANC headset isall about going for the expensive hybrid solution, right? Not quite!

Even if you get ANC working flawlessly,there are other things to take into account: headset’s physical design, passivenoise cancellation, music quality, and so on.