Active Noise Cancellation is a fascinating feature  of high-end headphones that requires some rather  

complicated engineering. Headphones such as these  are able to eliminate or destroy unwanted noise  

that is produced by the external environment,  while simultaneously playing the desired music  

or audio that is sent from your smartphone. In a nutshell, headphones such as these do  

this by using a microphone to measure the  unwanted noise produced by the environment  

and then calculating an anti-sound wave. This  anti-sound wave is added to the waveform of  

your music or audio, and when the combined  waveform is played through the headphone’s  

speaker, the external noise is eliminated or  canceled out, and just the desired audio remains. 

That’s the basic principle, but there’s a lot of  intricate engineering that underpins active noise  

cancellation. In order to better understand the  engineering, it’s easier to visualize sound waves  

not as these sinusoidal patterns but rather  as a set of traveling high-pressure zones,  

known as compressions, and low-pressure  zones, known as rarefactions. 

Let’s say you live or work next to a highway.  All the cars and trucks that zoom by generating  

a sound with a waveform such as this, which is  really just a sequence of traveling high pressure  

and low-pressure zones. These compressions  and rarefactions move through the air,  

and when they hit your eardrum,  you hear the sounds of the highway. 

In order to produce an anti-sound wave for the  highway’s noise, a sound wave must be generated  

that is equal and opposite. By that, we mean  that for every high-pressure zone from the noise,  

a low-pressure zone needs to be generated,  and for every low-pressure zone from the noise  

a high-pressure zone needs to be generated.  The noise and anti-noise meet, and when these  

low-pressure zones and high-pressure zones meet  or vice versa, they average out in that area,  

thereby eliminating the sounds from the highway. There are a few engineering challenges with  

this solution. First, the headphones or earbuds  them-selves provide some passive noise insulation,  

and therefore we need two microphones. One  microphone is used on the outside to measure  

the noise itself, and a second microphone  is used on the inside of the head-phones  

to measure the percentage of noise that’s  getting through the sound insulating  

properties of the headphones and into your ear. The second challenge is that it’s rather difficult  

to perfectly time the anti-sound wave with the  external noise. The noise from the highway has  

hundreds of compressions and rarefactions every  single second, so, if the anti-sound wave is off  

by a few milliseconds, then the noise cancellation  won’t work properly. Therefore, a high-powered  

digital processor is used to measure and calculate  the perfect anti-sound wave, while simultaneously,  

the interior microphone is monitoring whether  the active noise cancellation is in fact working  

properly. Note that active noise cancellation  is more effective for low frequency, repetitive  

noises because they have only a couple hundred  peaks and troughs, or wavelengths every second,  

but high-frequency noises have thousands  of wavelengths per second. If there’s even  

the smallest inaccuracy in timing the anti-sound  wave with the high frequency noise, the resulting  

combination between the anti-sound wave and  the high frequency noise will be ineffective. 

The third challenge, managed by the processor  and circuitry is that the anti-sound waveform  

needs to be combined with the audio waveform that  is sent from your smartphone. The audio plus the  

anti-sound acts just like different instruments in  a song and they combine to make a new sound which  

is played through the single speaker. When  the combined audio plus anti-sound waveform  

and the noise from the environment mix, the  anti-sound component of the combined waveform  

and the noise from the environment cancel out,  and we are left to hear just the desired audio. 

We made a separate episode that goes over  the different components of these headphones  

and we’re working on future episodes that  will cover other feats of engineering such  

as Bluetooth communication, the antenna, and the  micro-electrical mechanical system microphones. 

This video was made possible by our sponsor  

PCBWay. PCBWay can quickly manufacture  your PCBs with competitive prices,  

impeccable standards and they also provide  PCB assembly services where they populate and  

solder the components to the PCB. Check them  out using the link in the description below. 

Also, one quick note about this 3D model. These  are the Apple AirPods 2, which don’t actually  

have an active noise cancellation feature. In  order to model the interior of these headphones,  

we have to get detailed pictures of each  component, which as you see can be rather  

destructive. We have exterior models of these  other rather expensive headphones which do provide  

active noise cancellation, but no interior models  of them. Sorry for the switch up which we hope  

wasn’t too confusing. Furthermore, check out the  creator’s comments in the English Canada Subtitles  

where we discuss the difficulties of  implement noise cancellation in a room. 

We’d also like to thank all of our YouTube  and Patreon sponsors for helping us build  

these in-depth engineering explanations. You  can also provide your support by subscribing,  

liking this video, and commenting below. This  is Branch Education, Thanks for watching.