WEBVTT - How Active Noise Cancellation Works 0:00:04.480 --> 0:00:12.480 Welcome to tech Stuff, a production from iHeartRadio. Hey there, 0:00:12.520 --> 0:00:16.280 and welcome to tech Stuff. I'm your host, Jonathan Strickland. 0:00:16.320 --> 0:00:20.040 I'm an executive producer with iHeart Podcasts and how the 0:00:20.120 --> 0:00:23.720 tech are you? So today I figured I would talk 0:00:23.760 --> 0:00:29.880 about noise canceling technologies specifically in headphones, although you can 0:00:30.120 --> 0:00:34.360 employ these technologies in other use cases. And it's largely 0:00:34.400 --> 0:00:38.120 because I'm actually wearing a pair of noise canceling headphones 0:00:38.560 --> 0:00:42.120 right now as I record this episode. I'll talk more 0:00:42.200 --> 0:00:45.479 about those headphones in a future episode. I'm actually just 0:00:45.800 --> 0:00:48.720 trying them out now to make sure that I like 0:00:48.760 --> 0:00:50.879 how they work and all of that. But for now, 0:00:50.920 --> 0:00:53.960 I just wanted to talk about the science and technology 0:00:54.240 --> 0:01:01.400 behind active noise canceling or active noise reduction headphones. An 0:01:01.560 --> 0:01:06.040 R and ANC are the acronyms or initialisms, I should say, 0:01:06.040 --> 0:01:10.199 not acronyms that are used for those technologies. Now, noise 0:01:10.280 --> 0:01:14.399 canceling is more than just muffling sound. You can have 0:01:14.720 --> 0:01:18.600 passive noise canceling, which really just means things like ear 0:01:18.640 --> 0:01:22.559 plugs or really well insulated ear muffs. So it's more 0:01:22.600 --> 0:01:26.000 than that. It's not just soundproofing your ears or something. 0:01:26.280 --> 0:01:30.120 It's using technology to actively cancel out the sound waves 0:01:30.120 --> 0:01:32.839 that are heading for your ear drums. But we won't 0:01:32.840 --> 0:01:37.560 get ahead of ourselves. First, let's talk about what sound is. So, 0:01:38.120 --> 0:01:42.000 when you get down to it, sound is vibration, and 0:01:42.040 --> 0:01:46.240 we can think of vibration as energy. So this energy 0:01:46.319 --> 0:01:50.840 needs a medium to travel through. Sound travels through matter, 0:01:51.320 --> 0:01:54.200 and it doesn't matter if the matter is solid, liquid, 0:01:54.480 --> 0:01:57.720 or gas. It can travel through it, but it definitely 0:01:57.800 --> 0:02:00.480 needs to have a medium in order to try. This 0:02:00.560 --> 0:02:03.520 is why out in space there is no sound. You know, 0:02:03.760 --> 0:02:06.480 in space, no one can hear you scream. Well, that's 0:02:06.520 --> 0:02:10.560 because in space you have these vast regions where there 0:02:10.600 --> 0:02:15.200 is so little matter out there that sound cannot pass 0:02:15.520 --> 0:02:19.480 through it. There's nothing for the sound to transfer energy to. 0:02:19.960 --> 0:02:22.240 So it's not just that it's a lack of air, 0:02:22.480 --> 0:02:25.240 it's that it's a lack of anything, or at least 0:02:25.520 --> 0:02:29.160 there's not enough significant amount of anything out there that 0:02:29.200 --> 0:02:32.839 would allow for the transfer of longitudinal waves. By the way, 0:02:32.880 --> 0:02:36.840 that's how sound travels. Sound travels in longitudinal waves. So 0:02:37.040 --> 0:02:40.239 broadly speaking, there are two types of waves. There's longitudinal 0:02:40.480 --> 0:02:44.080 and there's transverse. Transverse waves are what I think a 0:02:44.120 --> 0:02:47.680 lot of folks imagine when they think of waves, often 0:02:47.720 --> 0:02:50.400 it's how we plot waves on a chart. It's a 0:02:50.480 --> 0:02:53.160 very easy way of doing it. So one way you 0:02:53.200 --> 0:02:57.680 could actually see transverse waves in action is just with 0:02:57.760 --> 0:03:00.720 a length of rope, a nice long length of The 0:03:00.800 --> 0:03:03.440 longer the better, really, because it's easier to see. And 0:03:03.600 --> 0:03:05.560 if you had a long length of rope and you 0:03:05.639 --> 0:03:08.320 picked up just one end of it, it's laid out 0:03:08.400 --> 0:03:11.120 straight in front of you. Then you started to move 0:03:11.200 --> 0:03:14.320 the end of the rope from side to side, left 0:03:14.320 --> 0:03:17.000 to right back again, over and over again. You would 0:03:17.040 --> 0:03:21.520 see waves traveled down the length of the rope. But 0:03:21.639 --> 0:03:24.520 this means that the wave is traveling at like a 0:03:24.639 --> 0:03:29.480 ninety degree angle from the disturbance of the medium, because 0:03:29.520 --> 0:03:32.880 again you're moving the rope left and right. You're not 0:03:33.080 --> 0:03:35.880 pushing on the rope. You're moving the rope left and right, 0:03:35.880 --> 0:03:38.760 but the waves are traveling down the rope. By the way, 0:03:38.800 --> 0:03:40.880 the same thing would happen if you were moving the 0:03:41.200 --> 0:03:43.960 rope up and down right. If you moved them up 0:03:43.960 --> 0:03:46.680 and down, you would still see the disturbance happening up 0:03:46.680 --> 0:03:49.320 and down, but the direction of the waves travel would 0:03:49.360 --> 0:03:53.080 be forward down the length of rope. Now, a longitudinal 0:03:53.160 --> 0:03:57.800 wave is different. The wave travels in the same direction 0:03:58.280 --> 0:04:02.080 as the disturbance rather at a ninety degree angle from it. 0:04:02.200 --> 0:04:04.800 So in this case, if the rope behaved like a 0:04:04.840 --> 0:04:08.160 longitudinal wave, if you pushed on the end of the rope, 0:04:08.480 --> 0:04:12.520 you would see the disturbance and wave traveled down the length. 0:04:12.640 --> 0:04:15.400 But that doesn't happen with rope. However, it does happen 0:04:15.680 --> 0:04:19.560 with one of the most important tools in any serious 0:04:19.800 --> 0:04:24.640 scientist's tool box. I'm talking about a slinky for fun. 0:04:25.160 --> 0:04:27.920 It's a wonderful toy. So if you take a slinky 0:04:28.320 --> 0:04:30.720 and you stretch it out a little bit between two people, 0:04:30.960 --> 0:04:32.960 and then you ask one of those two people to 0:04:33.640 --> 0:04:36.760 push the slinky forward really quickly, you would observe that 0:04:36.960 --> 0:04:40.600 you would see a wave travel forward through the slinky 0:04:40.839 --> 0:04:44.000 in the direction of the push. Areas of the slinky 0:04:44.160 --> 0:04:48.600 would compress as this wave travels down, and in fact, 0:04:48.800 --> 0:04:52.240 in the longitudinal wave business, we would call that compression. 0:04:52.600 --> 0:04:56.040 Areas where the slinky links would be further apart as 0:04:56.080 --> 0:04:58.880 the wave would travel through the medium, we would call 0:04:58.960 --> 0:05:03.400 that rare faction. So you have rare faction and compression. 0:05:04.040 --> 0:05:07.520 Now for the purposes of illustration, we often will draw 0:05:07.720 --> 0:05:11.479 sound waves almost as if they were transverse waves. It's 0:05:11.520 --> 0:05:15.000 just easier to see the parts of a wave that way. 0:05:15.360 --> 0:05:17.840 So if we did that, if we had like your 0:05:18.080 --> 0:05:21.279 your regular little graph, and we had a sound wave 0:05:21.440 --> 0:05:25.719 drawn on there, similar to a transverse wave, you would 0:05:25.760 --> 0:05:29.040 have peaks and you would have valleys, right, because that's 0:05:29.080 --> 0:05:33.040 the way we envision these, these transverse waves. And it's 0:05:33.080 --> 0:05:36.280 pretty simple to see a single wavelength, you know. You 0:05:36.360 --> 0:05:40.440 just go from one peak to the following peak. That's 0:05:40.520 --> 0:05:44.159 one wavelength. And it's not too hard to understand stuff 0:05:44.279 --> 0:05:49.640 like amplitude and frequency. So amplitude describes how high those 0:05:49.640 --> 0:05:52.320 peaks are from the center line, or how low the 0:05:52.360 --> 0:05:55.120 troughs are, if you will, And we would say that 0:05:55.160 --> 0:05:59.480 this correlates to volume with sound waves. Frequency would be 0:05:59.760 --> 0:06:03.320 how how many wavelengths are passing a given point in 0:06:03.400 --> 0:06:07.720 a fixed amount of time. This correlates to a sound's pitch. 0:06:08.160 --> 0:06:11.960 The higher frequencies are higher pitches. But it would be 0:06:12.040 --> 0:06:15.800 more accurate to illustrate this as a longitudinal wave, because 0:06:15.800 --> 0:06:20.280 that's how sound travels. Wavelengths and longitudinal waves refer to 0:06:20.320 --> 0:06:23.640 the distance between say one point of compression to the 0:06:23.680 --> 0:06:27.480 next point of compression, or we could actually measure it 0:06:27.520 --> 0:06:30.919 from one point of rarefaction to the next point of 0:06:31.000 --> 0:06:34.640 rare affection. That would still be a wavelength. Frequency is 0:06:34.839 --> 0:06:39.000 fairly simple. It's the number of compressions or rare factions, 0:06:39.000 --> 0:06:41.719 depending on which one you're starting with. In other words, 0:06:41.800 --> 0:06:45.279 the number of wavelengths that pass a given point in 0:06:45.320 --> 0:06:48.919 a fixed amount of time. Amplitude is a little bit different. 0:06:49.279 --> 0:06:54.000 It's the distance between points of compression within the sound wave. 0:06:54.400 --> 0:06:57.279 If a sound wave has many points of compression that 0:06:57.320 --> 0:07:01.040 are close to one another, it's high amplitude a loud sound. 0:07:01.360 --> 0:07:04.320 If there's a wave that has fewer points of compression 0:07:04.320 --> 0:07:06.520 and that maybe they're a little further apart from each other, 0:07:06.760 --> 0:07:11.440 it's low amplitude. Its lower volume. So with sound, we 0:07:11.520 --> 0:07:16.080 have something that's causing a vibration, and it could be anything, right. 0:07:16.120 --> 0:07:19.200 It could be a tree following in the forest as 0:07:19.240 --> 0:07:21.520 long as someone's there to hear it. It might be 0:07:21.560 --> 0:07:23.840 a flower pot falling on the pavement. It could be 0:07:23.880 --> 0:07:27.680 a fiddler drawing a bow across violin strings. It might 0:07:27.720 --> 0:07:31.080 be a mine being tortured. It could be anything. The 0:07:31.200 --> 0:07:34.600 sound travels out in all directions from the source, and 0:07:34.640 --> 0:07:38.200 it travels through whatever medium it's in. The sound most 0:07:38.200 --> 0:07:40.760 of us encounter most of the time is traveling through air, 0:07:40.920 --> 0:07:44.640 but this also works underwater or even through solid matter. Now, 0:07:44.640 --> 0:07:47.720 if these vibrations fall within the range of human hearing, 0:07:48.160 --> 0:07:50.920 then we might very well hear them, as long as 0:07:50.960 --> 0:07:53.200 we're close enough for those vibrations to get to us 0:07:53.480 --> 0:07:56.640 before they peter out. That's called attenuation. By the way, 0:07:56.920 --> 0:08:00.840 the sound attenuates as it travels from its source, That 0:08:00.960 --> 0:08:05.040 means it gets weaker as it travels out further from 0:08:05.080 --> 0:08:07.880 the source of sound, which makes sense right. Otherwise we 0:08:07.880 --> 0:08:10.240 wouldn't be able to hear anything. Everything would just be 0:08:10.320 --> 0:08:13.440 equally loud to us all the time, or it would 0:08:13.440 --> 0:08:16.640 be of the same amplitude as the original sound was 0:08:16.880 --> 0:08:19.840 and we'd all be deafened by it. So yeah, sound 0:08:20.440 --> 0:08:24.760 diminishes in strength as it travels. Now, the range of 0:08:25.240 --> 0:08:30.040 typical human hearing falls between twenty hurts or twenty vibrations 0:08:30.040 --> 0:08:34.400 per second up to twenty killer hurts or twenty thousand 0:08:34.559 --> 0:08:38.680 vibrations per second. Now, as I mentioned earlier, the lower 0:08:38.720 --> 0:08:43.959 frequencies have lower pitches, So a twenty hurtz sound would 0:08:43.960 --> 0:08:47.160 be a very deep bass sound. In fact, some of 0:08:47.200 --> 0:08:51.240 those you might feel more than you hear them, depending 0:08:51.320 --> 0:08:54.600 upon your hearing, and as we get older, we typically 0:08:54.600 --> 0:08:57.440 lose some of the ability to hear the higher pitches. 0:08:57.640 --> 0:09:00.080 I think the last hearing test I did said my 0:09:00.120 --> 0:09:03.640 hearing kind of tops out around fifteen or sixteen killer hurtz, 0:09:04.000 --> 0:09:07.480 So thatre's a lot of space between the upper limits 0:09:07.520 --> 0:09:10.840 of my hearing and the typical range for human hearing. 0:09:11.080 --> 0:09:13.319 Part of that is just because I'm old, and part 0:09:13.360 --> 0:09:15.280 of that is also because I saw a lot of 0:09:15.360 --> 0:09:19.200 rock concerts or rock shows. I can't call them concerts 0:09:19.280 --> 0:09:22.280 rock shows when I was in college, thanks to Dick 0:09:22.400 --> 0:09:25.200 Dale and the Dell Tones and the Hate Bombs and 0:09:25.240 --> 0:09:28.200 the Woggles and all the other bands I saw that 0:09:28.280 --> 0:09:30.720 ruined my hearing. It's really my fault. I should have 0:09:30.720 --> 0:09:35.520 worn earplugs anyway. Younger people can still hear those higher 0:09:35.520 --> 0:09:38.559 frequencies typically. I mean we always have to say typically, 0:09:38.559 --> 0:09:41.680 because there are obviously exceptions. But you may have heard 0:09:41.720 --> 0:09:45.280 that some businesses have even installed speakers that would play very, 0:09:45.920 --> 0:09:49.920 very high pitched sounds in order to discourage youngsters from 0:09:50.160 --> 0:09:54.040 loitering at that place of business, Like convenience stores and stuff, 0:09:54.200 --> 0:09:57.000 so the adults could shop in peace, and all those young, 0:09:57.160 --> 0:10:00.520 unruly hooligans would be chased out by unpleas a high 0:10:00.600 --> 0:10:03.559 pitched noise. I did a cursory search on this and 0:10:03.559 --> 0:10:08.079 found devices that are called mosquito alarms. These alarms push 0:10:08.080 --> 0:10:11.760 out sound at high amplitude. But if you're like me 0:10:12.360 --> 0:10:16.320 and you've lost hearing in those frequency ranges, well it 0:10:16.400 --> 0:10:19.120 don't bug you none. You don't hear it even though 0:10:19.160 --> 0:10:21.920 it's being played at high volume. But meanwhile, all the 0:10:21.960 --> 0:10:24.880 little tykes grab their ears and run off, and it 0:10:24.960 --> 0:10:27.880 leaves me to buy my slim gems in peace. I'm 0:10:27.880 --> 0:10:31.000 mostly kidding about that. I'm not that grouchy. I'm not 0:10:31.040 --> 0:10:36.360 really a fan of making spaces inherently unwelcome to slices 0:10:36.360 --> 0:10:39.800 of demographics. Also, I don't eat slim gems. Apologies to 0:10:39.920 --> 0:10:44.760 Randy Savage. Anyway. Let's talk about the perception of sound. 0:10:45.080 --> 0:10:49.359 So when sound waves enter our ears, the wave travels 0:10:49.559 --> 0:10:52.400 to the tympanic membrane, which is also known as the 0:10:52.440 --> 0:10:56.559 ear drum. So the sound wave transfers vibrations to this membrane, 0:10:56.600 --> 0:10:59.280 and it's actually doing that through very small changes in 0:10:59.360 --> 0:11:03.120 air pressure in our ear canals, so these small changes 0:11:03.160 --> 0:11:07.520 in air pressure are essentially pushing and pulling against that membrane. Now, 0:11:07.520 --> 0:11:11.680 the membrane in turn transfers those vibrations to three very 0:11:11.880 --> 0:11:15.600 tiny delicate bones in our middle ears. Those are the hammer, 0:11:15.760 --> 0:11:18.440 the anvil, and the stirrup, and they're called that because 0:11:18.440 --> 0:11:20.760 that's kind of what they look like. And these tiny 0:11:20.800 --> 0:11:25.000 bones kind of act like an amplifier, and they send 0:11:25.040 --> 0:11:28.880 the vibrations further along into the inner ear, where a 0:11:29.240 --> 0:11:33.839 snail shaped structure called the cochlea sits. Now, the cochlea 0:11:34.160 --> 0:11:38.280 contains fluid within it, and the vibrations to the cochlea 0:11:38.360 --> 0:11:41.880 make this fluid ripple. This in turn creates a wave 0:11:42.040 --> 0:11:45.120 on the membrane that lines the cochlea. And there are 0:11:45.160 --> 0:11:50.280 these little hair like protrusions inside the cochlea. They're called stereocilia. 0:11:50.760 --> 0:11:55.840 They vibrate from all this rippling, and they transfer those vibrations, 0:11:55.880 --> 0:12:00.600 this physical vibration into electrical impulses. Those impulse is then 0:12:00.679 --> 0:12:04.400 travel to our brains and the brain interprets the these 0:12:04.440 --> 0:12:08.679 a sound. So ultimately the sounds we encounter are in 0:12:08.720 --> 0:12:12.240 a sense all in our heads. Thus the question if 0:12:12.280 --> 0:12:14.480 a tree falls in the forest and no one is 0:12:14.520 --> 0:12:16.640 there to hear it, does it make a sound? You 0:12:16.679 --> 0:12:20.680 could argue, really, sound only exists within the mind, and 0:12:20.720 --> 0:12:23.080 if there is no mind to perceive it, there is 0:12:23.160 --> 0:12:27.080 no sound. Our brains create the perception of that sound. 0:12:27.400 --> 0:12:31.240 So this raises a question, is what we hear actually 0:12:31.440 --> 0:12:34.800 what is happening out in reality? If somehow we were 0:12:34.840 --> 0:12:38.720 able to step outside of the experience of being human 0:12:39.040 --> 0:12:43.800 and to perceive things as they truly are, would sounds 0:12:44.000 --> 0:12:47.960 appear to be anything like what we perceive. Now that's 0:12:48.000 --> 0:12:51.160 a question for philosophers, but you know, it sure would 0:12:51.200 --> 0:12:54.000 be interesting if we found out that every single person's 0:12:54.040 --> 0:12:59.439 experiences sound differently like. It's just that collectively we all 0:12:59.480 --> 0:13:02.600 agree that the thing causing the sound is awesome, like 0:13:02.679 --> 0:13:05.480 maybe a new they might be Giant's song, or that 0:13:05.559 --> 0:13:09.120 it's awful like a new kid rock song. Just having 0:13:09.160 --> 0:13:12.400 fun here, But no, Seriously, because it's impossible for us 0:13:12.480 --> 0:13:15.520 to step into the experience of someone else, we can't 0:13:15.600 --> 0:13:18.920 really be sure that the way we experience sound is 0:13:18.960 --> 0:13:22.520 the same as what other people experience kind of the 0:13:22.559 --> 0:13:24.440 same way. That there's no way for me to know 0:13:24.880 --> 0:13:27.160 if the shade of blue I see when I look 0:13:27.200 --> 0:13:30.000 in the sky is the same experience you have when 0:13:30.040 --> 0:13:32.520 you do the same thing. Now, I know I'm getting 0:13:32.559 --> 0:13:36.800 a little bit whibbly wobbly here, But acoustics, the science 0:13:37.160 --> 0:13:41.400 of sound involves a lot of psychology. If you listen 0:13:41.440 --> 0:13:44.200 to my episodes about the MP three format, you know 0:13:44.320 --> 0:13:48.440 that one way MP three's can serve filespace is the 0:13:48.480 --> 0:13:53.720 compression algorithm ditches any sounds deemed to be beyond human perception. 0:13:54.000 --> 0:13:57.040 Like if a very quiet sound follows a very loud sound, 0:13:57.280 --> 0:13:59.880 typically we can't hear the quiet one. The loud one 0:14:00.200 --> 0:14:02.480 as almost kind of deadened ust to being able to 0:14:02.520 --> 0:14:04.520 hear the quiet one. And I'm talking about like these 0:14:04.559 --> 0:14:07.120 sounds are like back to back one raft or the other. 0:14:07.400 --> 0:14:10.880 So the compression algorithm would say, oh, well, no one's 0:14:10.920 --> 0:14:12.520 going to be able to hear the second sound in 0:14:12.559 --> 0:14:14.600 the first place, so why would be encode it? Just 0:14:14.679 --> 0:14:18.360 leave it out, and thus it conserves filespace. Of course, 0:14:18.360 --> 0:14:20.960 if you start to ditch stuff humans actually can perceive, 0:14:21.160 --> 0:14:23.480 you begin to affect the quality of sound, and then 0:14:23.520 --> 0:14:27.240 you have problems with the decline and quality. All right, 0:14:27.560 --> 0:14:30.320 I've got tons more to say, and Obviously, we haven't 0:14:30.320 --> 0:14:33.080 even gotten to active noise cancelation yet, So let's take 0:14:33.120 --> 0:14:44.640 a quick break and we'll be right back. Okay, we're back, 0:14:44.680 --> 0:14:48.520 and we're going back to sound waves. So you might 0:14:48.600 --> 0:14:53.120 recall that the speed of light is constant, which is 0:14:53.560 --> 0:14:56.960 kind of true, but not all the truth. The speed 0:14:56.960 --> 0:15:00.920 of light is constant given the medium through which it travels. 0:15:01.240 --> 0:15:04.800 When light from the Sun reaches Earth, it actually slows 0:15:04.880 --> 0:15:08.040 down a little bit as that light hits our atmosphere. 0:15:08.200 --> 0:15:11.040 And by a little bit, I mean a very small amount, 0:15:11.120 --> 0:15:15.320 small enough to be deemed insignificant based upon like the 0:15:15.400 --> 0:15:17.880 speed it travels through a vacuum versus the speed it 0:15:17.920 --> 0:15:21.920 travels through air, insignificant for most calculations. I mean, it 0:15:21.960 --> 0:15:25.200 does happen, but it's a very tiny change. The ratio 0:15:25.200 --> 0:15:27.600 of difference between the faster and slower rates is called 0:15:27.640 --> 0:15:30.960 the refractive index. I'm getting a little off topic, although 0:15:30.960 --> 0:15:33.800 the same thing kind of happens with sound too, But sound, 0:15:34.080 --> 0:15:38.080 like light, will travel at different speeds depending upon the 0:15:38.120 --> 0:15:42.880 medium through which it travels. Moreover, the temperature of the 0:15:43.000 --> 0:15:46.800 medium will affect how fast sound is able to travel 0:15:46.840 --> 0:15:51.000 through it. Sound travels faster through hot air than it 0:15:51.040 --> 0:15:54.080 does through cold air. Now, when you think about it, 0:15:54.160 --> 0:15:59.520 that makes sense. Sound is vibration. Hot air has molecules 0:15:59.520 --> 0:16:02.880 and atom They have more energy in them, so they're 0:16:02.920 --> 0:16:06.560 more inclined to vibrate. They're already moving around. They'll carry 0:16:06.640 --> 0:16:10.280 movement more easily than cold air does because cold air 0:16:10.520 --> 0:16:14.520 has less energy in it, so the vibrations come less readily. 0:16:14.840 --> 0:16:17.840 This gets reflected in the speed of sound. Sound traveling 0:16:17.840 --> 0:16:20.920 on a day that's around sixty degrees fahrenheit, we'll move 0:16:20.960 --> 0:16:24.720 it about two and twenty kilometers per hour. But let's 0:16:24.720 --> 0:16:28.440 say it's a really chilly night, like negative sixty seven 0:16:28.520 --> 0:16:31.600 degrees fahrenheit. Then you're talking about sound travel I get 0:16:31.640 --> 0:16:35.320 around one than fifty six kilometers per hour. Though, you know, 0:16:35.360 --> 0:16:37.640 if you're out in weather that's that cold, the speed 0:16:37.640 --> 0:16:40.160 of sound probably isn't is you know, not top of 0:16:40.280 --> 0:16:43.200 mind to you. You're probably thinking, how do I get 0:16:43.240 --> 0:16:46.040 inside before I freeze to death. Now let's get back 0:16:46.080 --> 0:16:49.680 to sound waves in order to understand how noise cancelation 0:16:49.840 --> 0:16:53.320 actually works. All right, So I mentioned earlier. Sound waves 0:16:53.560 --> 0:16:57.200 have wavelengths, and we describe the frequency of sound by 0:16:57.240 --> 0:17:00.680 the number of wavelengths that pass a fixed point in 0:17:00.800 --> 0:17:04.000 space within a given amount of time. So if we're 0:17:04.040 --> 0:17:07.280 using hurts as our measurement, the amount of time is 0:17:07.400 --> 0:17:10.240 one second. So let's say that you are able to 0:17:10.359 --> 0:17:13.600 see sound waves and you're able to count really fast, 0:17:13.720 --> 0:17:16.439 like time to you doesn't pass the same way it 0:17:16.480 --> 0:17:20.240 does to everybody else, and you use a stop watch 0:17:20.440 --> 0:17:23.440 so that you can click down a single second. Meanwhile, 0:17:23.560 --> 0:17:27.000 you're counting all the sound waves that go past you. Well, 0:17:27.320 --> 0:17:29.359 if you did that, the number you would come up 0:17:29.400 --> 0:17:33.159 to that would be the sound's frequency. In hurts, the 0:17:33.200 --> 0:17:36.280 amount of time it takes just one wavelength to pass 0:17:36.359 --> 0:17:39.760 a fixed point is called a period. So for a 0:17:39.880 --> 0:17:44.399 twenty Hurtz sound, a period is just one twentieth of 0:17:44.480 --> 0:17:47.119 a second. That's how long it would take a single 0:17:47.160 --> 0:17:50.560 wavelength to complete one cycle. So if we were to 0:17:50.760 --> 0:17:54.760 further divide that period into even smaller fractions, we could 0:17:54.760 --> 0:17:58.600 call those phases. To get into phases in detail would 0:17:58.640 --> 0:18:01.960 really require visual aid, because otherwise I would just start 0:18:02.000 --> 0:18:04.640 spouting off formula to you and it would all get 0:18:04.760 --> 0:18:08.840 very confusing for me. Really. I mean, you might be fine, 0:18:09.200 --> 0:18:11.919 but I would inevitably say something wrong. So I'm not 0:18:11.960 --> 0:18:14.800 even gonna bother doing it because I'll just mess it up. 0:18:15.119 --> 0:18:18.320 But if you have two or more waves, and let's 0:18:18.359 --> 0:18:20.280 say all of these waves, these are sound waves, they 0:18:20.280 --> 0:18:23.760 are longitudinal. So let's say all these waves are aligned 0:18:23.840 --> 0:18:27.119 in that they have the same areas of compression and rarefaction. 0:18:27.520 --> 0:18:30.600 As they travel past a fixed point, those sound waves 0:18:30.600 --> 0:18:33.560 would be said to be in phase with one another. 0:18:34.080 --> 0:18:37.720 They're all kind of traveling at the same speed in 0:18:37.800 --> 0:18:41.280 the same direction. But let's say you have sound wave 0:18:41.359 --> 0:18:44.600 A and it travels with its various compression and rare 0:18:44.640 --> 0:18:48.560 faction zones, and then you've got sound wave B. But 0:18:48.760 --> 0:18:54.159 soundwave b's compression zones are matching with a's rarefaction zones, 0:18:54.440 --> 0:18:58.200 and b's rarefaction zones are matching with a's compression zones. 0:18:58.280 --> 0:19:01.159 So they're opposite. They're like the opposite sides of a 0:19:01.200 --> 0:19:04.840 puzzle fitting in together. And let's say they match each 0:19:04.840 --> 0:19:08.200 other in amplitude, so they're both the same volume. Well 0:19:08.200 --> 0:19:11.560 what happens at that point, Well, what happens is they 0:19:11.640 --> 0:19:17.639 cancel each other out. It's called destructive interference. Essentially, it 0:19:17.680 --> 0:19:20.359 all comes down to math. If we were to assign 0:19:20.600 --> 0:19:25.000 values to these waves, then maybe we say wave A 0:19:25.520 --> 0:19:29.560 is at value two at a given point, while wave 0:19:29.640 --> 0:19:32.640 B is at negative two. So then we add these 0:19:32.640 --> 0:19:36.280 two together two plus negative two equals zero. Now that 0:19:36.400 --> 0:19:39.560 is an oversimplification of what's going on here, but it's 0:19:40.000 --> 0:19:44.320 basically the concept behind noise cancelation. Now, if we think 0:19:44.359 --> 0:19:47.840 of transverse waves, which I think are easier to imagine, 0:19:48.000 --> 0:19:50.920 this would be like having two waves where the peaks 0:19:51.160 --> 0:19:54.480 of wave A are matched up with the values of 0:19:54.600 --> 0:19:58.760 wave B and vice versa, and that the height the 0:19:58.800 --> 0:20:02.760 amplitude of those peaks and valleys is exactly the same, 0:20:02.960 --> 0:20:06.680 and what we get ultimately is cancelation. The two waves 0:20:06.840 --> 0:20:09.400 sound waves in this case, eliminate each other and we 0:20:09.440 --> 0:20:12.960 hear nothing as a result. Or if you prefer those 0:20:13.040 --> 0:20:16.440 differences in air pressure that happens in our ear canals 0:20:16.480 --> 0:20:20.439 that ultimately we end up perceiving as sound. Those differences 0:20:20.560 --> 0:20:25.440 never happen because while one sound wave is pushing one way, 0:20:25.800 --> 0:20:28.520 the other sound wave is pushing the other way with 0:20:28.680 --> 0:20:32.119 equal force, and the air particles don't do anything, they 0:20:32.160 --> 0:20:36.000 don't go anywhere, So therefore we hear nothing. But getting 0:20:36.040 --> 0:20:39.520 to that point where we could actually create technology that 0:20:39.560 --> 0:20:43.879 could detect incoming sound and then produce out of phase 0:20:44.080 --> 0:20:48.000 equivalence for the purposes of eliminating that sound. That would 0:20:48.040 --> 0:20:51.479 take a lot of time, the better part of a 0:20:51.560 --> 0:20:56.399 century actually now. One person who suggested an approach to 0:20:56.440 --> 0:21:00.159 do this was a doctor of philosophy and medicine in 0:21:00.200 --> 0:21:04.560 Germany back in the nineteen thirties. His name was Paul Lug, 0:21:05.040 --> 0:21:08.720 and he applied for a patent that he titled process 0:21:08.960 --> 0:21:14.320 of Silencing Sound Oscillations. Now, the patent application begins by 0:21:14.359 --> 0:21:17.639 explaining that up to that point, the only way to 0:21:17.680 --> 0:21:22.280 cancel displeasing oscillations was to build in mechanical solutions at 0:21:22.320 --> 0:21:26.639 the source of the noise itself. His invention would allow 0:21:26.680 --> 0:21:31.280 for the installation of noise canceling technology that was independent 0:21:31.880 --> 0:21:35.600 of the source of the noise. So, instead of trying 0:21:35.600 --> 0:21:38.320 to figure out a way to mechanically alter a process 0:21:38.560 --> 0:21:41.680 so that it produced less noise, you could use Lug's 0:21:41.760 --> 0:21:45.240 invention to eliminate noise no matter where it came from, 0:21:45.560 --> 0:21:49.440 because this device would be able to take in incoming 0:21:49.480 --> 0:21:54.199 noise and produce the anti phase version of it. He 0:21:54.280 --> 0:21:58.239 described the basic components of noise cancelation, and in his 0:21:58.320 --> 0:22:03.520 description he mentioned microphones or receivers which would detect incoming 0:22:03.560 --> 0:22:08.680 sound waves and a quote unquote reproducing apparatus. In other words, 0:22:08.760 --> 0:22:12.000 essentially a loud speaker of some sort that would produce 0:22:12.119 --> 0:22:15.199 sounds having an opposite phase to the incoming noise. The 0:22:15.280 --> 0:22:18.160 opposing phase sound waves would then cancel each other out. 0:22:18.680 --> 0:22:22.240 Lug also mentioned ways to eliminate only part of a 0:22:22.320 --> 0:22:26.520 noise or only specific types of noises. So he thought 0:22:26.600 --> 0:22:29.200 this would be handy if you needed to eliminate noises 0:22:29.240 --> 0:22:32.199 and loud environments while still allowing people to speak with 0:22:32.240 --> 0:22:35.080 one another. So how do you eliminate noise but you 0:22:35.240 --> 0:22:38.679 allow signal to get through? That was what he was 0:22:38.720 --> 0:22:41.960 talking about. He was also thinking about ways to eliminate 0:22:42.160 --> 0:22:45.800 unwanted noises in places like say a theater or a 0:22:45.880 --> 0:22:49.040 concert hall, where maybe you go to the concert hall 0:22:49.400 --> 0:22:52.800 and the music is fantastic, but there's some element, some 0:22:53.119 --> 0:22:58.120 acoustic element in that environment. This is producing something that 0:22:58.359 --> 0:23:02.639 was not wanted, that is detracting from the experience of 0:23:02.720 --> 0:23:06.960 hearing this concert. Luke said, well, we could create this 0:23:07.280 --> 0:23:12.600 technology that would detect this unwanted frequency, like we would 0:23:12.680 --> 0:23:16.159 tune it to that and then produce the anti phase 0:23:16.240 --> 0:23:19.360 version and then you could just enjoy the concert as 0:23:19.400 --> 0:23:23.920 it was intended, without any of these unpleasant secondary noises 0:23:24.040 --> 0:23:29.679 mixed in. Now, Luke's idea was pretty solid. Unfortunately, the 0:23:29.800 --> 0:23:33.679 technology was nowhere near where it needed to be in 0:23:33.800 --> 0:23:38.600 order to actually realize his idea was He did get 0:23:38.600 --> 0:23:42.280 his patent, he got that, granted, but he was getting 0:23:42.280 --> 0:23:46.720 a lot of resistance in the academic world of Germany 0:23:46.800 --> 0:23:49.640 because I think a lot of other people realized they 0:23:49.800 --> 0:23:53.080 just couldn't accomplish what he was suggesting. Not that what 0:23:53.160 --> 0:23:57.479 he was saying was impossible from a science perspective, but 0:23:57.560 --> 0:24:01.720 on a technical level they couldn't figure it out. And moreover, 0:24:02.080 --> 0:24:05.440 things in Germany were obviously getting rather tense in the 0:24:05.560 --> 0:24:10.520 nineteen thirties as the world continued to plunge toward total 0:24:10.880 --> 0:24:13.560 war in the region. Now I tried to find out 0:24:13.600 --> 0:24:17.080 more information about lug and I did discover a paper 0:24:17.160 --> 0:24:20.080 that was written in German that was all about him 0:24:20.240 --> 0:24:26.320 and his life both before and after his proposed invention. Now, 0:24:26.359 --> 0:24:30.360 my German is awful. I am not at all fluent, 0:24:30.480 --> 0:24:35.359 so I depended heavily, really entirely on Google Translate, and 0:24:35.560 --> 0:24:39.760 was only partially successful in translating the article because the 0:24:39.800 --> 0:24:44.120