How Do Noise Canceling Headphones Work? — Transcript

Full transcript

1. 0:00Active Noise Cancellation is a fascinating feature  of high-end headphones that requires some rather
2. 0:07complicated engineering. Headphones such as these  are able to eliminate or destroy unwanted noise
3. 0:14that is produced by the external environment,  while simultaneously playing the desired music
4. 0:20or audio that is sent from your smartphone. In a nutshell, headphones such as these do
5. 0:26this by using a microphone to measure the  unwanted noise produced by the environment
6. 0:32and then calculating an anti-sound wave. This  anti-sound wave is added to the waveform of
7. 0:38your music or audio, and when the combined  waveform is played through the headphone’s
8. 0:44speaker, the external noise is eliminated or  canceled out, and just the desired audio remains.
9. 0:51That’s the basic principle, but there’s a lot of  intricate engineering that underpins active noise
10. 0:57cancellation. In order to better understand the  engineering, it’s easier to visualize sound waves
11. 1:03not as these sinusoidal patterns but rather  as a set of traveling high-pressure zones,
12. 1:10known as compressions, and low-pressure  zones, known as rarefactions.
13. 1:16Let’s say you live or work next to a highway.  All the cars and trucks that zoom by generating
14. 1:22a sound with a waveform such as this, which is  really just a sequence of traveling high pressure
15. 1:29and low-pressure zones. These compressions  and rarefactions move through the air,
16. 1:34and when they hit your eardrum,  you hear the sounds of the highway.
17. 1:39In order to produce an anti-sound wave for the  highway’s noise, a sound wave must be generated
18. 1:45that is equal and opposite. By that, we mean  that for every high-pressure zone from the noise,
19. 1:51a low-pressure zone needs to be generated,  and for every low-pressure zone from the noise
20. 1:57a high-pressure zone needs to be generated.  The noise and anti-noise meet, and when these
21. 2:03low-pressure zones and high-pressure zones meet  or vice versa, they average out in that area,
22. 2:10thereby eliminating the sounds from the highway. There are a few engineering challenges with
23. 2:16this solution. First, the headphones or earbuds  them-selves provide some passive noise insulation,
24. 2:23and therefore we need two microphones. One  microphone is used on the outside to measure
25. 2:29the noise itself, and a second microphone  is used on the inside of the head-phones
26. 2:34to measure the percentage of noise that’s  getting through the sound insulating
27. 2:38properties of the headphones and into your ear. The second challenge is that it’s rather difficult
28. 2:44to perfectly time the anti-sound wave with the  external noise. The noise from the highway has
29. 2:51hundreds of compressions and rarefactions every  single second, so, if the anti-sound wave is off
30. 2:58by a few milliseconds, then the noise cancellation  won’t work properly. Therefore, a high-powered
31. 3:05digital processor is used to measure and calculate  the perfect anti-sound wave, while simultaneously,
32. 3:12the interior microphone is monitoring whether  the active noise cancellation is in fact working
33. 3:18properly. Note that active noise cancellation  is more effective for low frequency, repetitive
34. 3:24noises because they have only a couple hundred  peaks and troughs, or wavelengths every second,
35. 3:31but high-frequency noises have thousands  of wavelengths per second. If there’s even
36. 3:36the smallest inaccuracy in timing the anti-sound  wave with the high frequency noise, the resulting
37. 3:43combination between the anti-sound wave and  the high frequency noise will be ineffective.
38. 3:49The third challenge, managed by the processor  and circuitry is that the anti-sound waveform
39. 3:55needs to be combined with the audio waveform that  is sent from your smartphone. The audio plus the
40. 4:01anti-sound acts just like different instruments in  a song and they combine to make a new sound which
41. 4:08is played through the single speaker. When  the combined audio plus anti-sound waveform
42. 4:13and the noise from the environment mix, the  anti-sound component of the combined waveform
43. 4:20and the noise from the environment cancel out,  and we are left to hear just the desired audio.
44. 4:27We made a separate episode that goes over  the different components of these headphones
45. 4:32and we’re working on future episodes that  will cover other feats of engineering such
46. 4:37as Bluetooth communication, the antenna, and the  micro-electrical mechanical system microphones.
47. 4:44This video was made possible by our sponsor
48. 4:47PCBWay. PCBWay can quickly manufacture  your PCBs with competitive prices,
49. 4:54impeccable standards and they also provide  PCB assembly services where they populate and
50. 5:01solder the components to the PCB. Check them  out using the link in the description below.
51. 5:07Also, one quick note about this 3D model. These  are the Apple AirPods 2, which don’t actually
52. 5:14have an active noise cancellation feature. In  order to model the interior of these headphones,
53. 5:19we have to get detailed pictures of each  component, which as you see can be rather
54. 5:25destructive. We have exterior models of these  other rather expensive headphones which do provide
55. 5:32active noise cancellation, but no interior models  of them. Sorry for the switch up which we hope
56. 5:39wasn’t too confusing. Furthermore, check out the  creator’s comments in the English Canada Subtitles
57. 5:46where we discuss the difficulties of  implement noise cancellation in a room.
58. 5:51We’d also like to thank all of our YouTube  and Patreon sponsors for helping us build
59. 5:56these in-depth engineering explanations. You  can also provide your support by subscribing,
60. 6:03liking this video, and commenting below. This  is Branch Education, Thanks for watching.