This is part 15 in a series on Headphone Specs, Drivers, DACs, Sound, and how all of them relate to each other. There’s a wealth of knowledge in these so don’t hesitate to open some more tabs, bookmark, and share!!
How Do Noise Cancelling Headphones Work? (This Article)
Hello there friend and Welcome aboard!!
Before we get into the question of how do noise cancelling headphones work, grab a snack, sit back and relax because..
You’ve come to the right place!!
What I will bring you in this review
How do noise cancelling headphones work?
Active vs. Passive
Now without further ado, let’s get rolling!!
For awhile I avoided noise cancelling headphones because I believed them to be more hype over substance. Bose has a pretty tight stranglehold on this market, and I just wasn’t feeling them all that much after my first experience.
Fast forward a few years and some other big names have added their own flavors into the mix, and the advent of Bluetooth has also exploded in popularity as well.
Nowadays for me, a headphone with Bluetooth is almost priceless given my busy schedule, and the fact that wires just aren’t all that convenient when I’m out and about.
I’ve gotten the chance to demo as well as own a few different pairs, and while they aren’t as good as headphones with a traditional cable, they are good enough for my purposes. For awhile I wasn’t quite sure how they worked from a scientific standpoint, but I found that the logistics behind the process is very fascinating and worthy of an article!
So let’s get into it!
How noise cancelling headphones work?
The process is fairly simple: Inside the housing of the ear-cup near the driver, there’s a small microphone that picks up the ambient noise (think of stuff like fans, air conditioners, people talking, traffic), mimics it by creating duplicates of the sound wave, and then cancels it out via a process known as phase cancellation, or destructive interference.
Think of the amplitude of each sound (the noise vs. the creation of that noise), to be mirror images of one another. This creates the silence.
To do this, the headphone requires 4 things:
A microphone to pick up the ambient noise.
Noise cancelling circuitry, to mimic the ambient noise that creates a new wave which is 180 degrees out of phase with the original.
A speaker to receive both of the sounds. The mimicked sound is destroyed by destructive interference, but doesn’t affect the original wave form.
A battery to create the energy needed for such a monumental task.
Active vs. Passive
Active noise cancelling headphones, like that of the Bose and Sony (and some Beats) variety, usually come equipped with a switch that enables the noise cancelling to take place. They are structured with a barrier that blocks high frequency sound waves, as well as low ones too.
Active NC headphones generally block out around 70% of noise, which is an effective reduction of about 20%. The misconception that a lot of people have is that they’re supposed to drown out every single sound that you could possibly hear which is simply unrealistic.
Even on a plane you’re still going to hear some things, but it won’t be enough to ruin your experience in most cases.
In fact, NC headphones do a good job of both cancelling unwanted noise as well as reducing fatigue, which is why a big part of the market comes in the form of users on an airplane.
Passive noise cancelling headphones are usually the ones with a circumaural (Around the ear) fit in a closed back system. Closed back vs. Open back headphones. Passive noise cancelling headphones are very good at isolating sound, but not necessarily cancelling it. You typically won’t be able to hear what’s going on around you at higher volumes, but there isn’t that vacuum seal that Active NC headphones create.
The Science behind it
Digging a little deeper, to understand how noise cancelling actually works we have to know what a sound wave is.
A sound wave is a 3-dimensional ripple through space, or in our case the air. The ripple and subsequent vibration is what creates the sound that our ears perceive.
The change in air pressure of said wave is called it’s amplitude, which determines how loud the sound is. It can also be defined as the size of the vibration.
The frequency is the speed of said vibration, and determines it’s pitch.
The crest is the highest point of the wave form, and the trough is it’s lowest point.
So, our 3D wave is groovin’ through space, and when you duplicate said wave and line it up in sync, (matching both the peak and trough) it basically creates a louder wave. This is what’s known as being in phase (Constructive interference).
However, if you match up the trough of one wave, with the peak of the other (and vice-versa), you get what we talked about before: Destructive interference, or out of phase (Phase cancellation).
This is in essence what an Active Noise Cancelling headphone does.
As I’ve mentioned in the open, I got a chance to try out some noise cancelling headphones and I think my favorites were the Bose QC35 based on what I’ve heard. When you first flick the switch, they provide a nice vacuum seal which isn’t too shocking, although it really does bother some people.
If you’re looking for a good model, I would recommend it, but keep in mind it’s very specialized. Interested in learning more about what I call “The pleasant homie?”