1 00:00:04,480 --> 00:00:12,480 Speaker 1: Welcome to tech Stuff, a production from iHeartRadio. Hey there, 2 00:00:12,520 --> 00:00:16,280 Speaker 1: and welcome to tech Stuff. I'm your host, Jonathan Strickland. 3 00:00:16,320 --> 00:00:20,040 Speaker 1: I'm an executive producer with iHeart Podcasts and how the 4 00:00:20,120 --> 00:00:23,720 Speaker 1: tech are you? So today I figured I would talk 5 00:00:23,760 --> 00:00:29,880 Speaker 1: about noise canceling technologies specifically in headphones, although you can 6 00:00:30,120 --> 00:00:34,360 Speaker 1: employ these technologies in other use cases. And it's largely 7 00:00:34,400 --> 00:00:38,120 Speaker 1: because I'm actually wearing a pair of noise canceling headphones 8 00:00:38,560 --> 00:00:42,120 Speaker 1: right now as I record this episode. I'll talk more 9 00:00:42,200 --> 00:00:45,479 Speaker 1: about those headphones in a future episode. I'm actually just 10 00:00:45,800 --> 00:00:48,720 Speaker 1: trying them out now to make sure that I like 11 00:00:48,760 --> 00:00:50,879 Speaker 1: how they work and all of that. But for now, 12 00:00:50,920 --> 00:00:53,960 Speaker 1: I just wanted to talk about the science and technology 13 00:00:54,240 --> 00:01:01,400 Speaker 1: behind active noise canceling or active noise reduction headphones. An 14 00:01:01,560 --> 00:01:06,040 Speaker 1: R and ANC are the acronyms or initialisms, I should say, 15 00:01:06,040 --> 00:01:10,199 Speaker 1: not acronyms that are used for those technologies. Now, noise 16 00:01:10,280 --> 00:01:14,399 Speaker 1: canceling is more than just muffling sound. You can have 17 00:01:14,720 --> 00:01:18,600 Speaker 1: passive noise canceling, which really just means things like ear 18 00:01:18,640 --> 00:01:22,559 Speaker 1: plugs or really well insulated ear muffs. So it's more 19 00:01:22,600 --> 00:01:26,000 Speaker 1: than that. It's not just soundproofing your ears or something. 20 00:01:26,280 --> 00:01:30,120 Speaker 1: It's using technology to actively cancel out the sound waves 21 00:01:30,120 --> 00:01:32,839 Speaker 1: that are heading for your ear drums. But we won't 22 00:01:32,840 --> 00:01:37,560 Speaker 1: get ahead of ourselves. First, let's talk about what sound is. So, 23 00:01:38,120 --> 00:01:42,000 Speaker 1: when you get down to it, sound is vibration, and 24 00:01:42,040 --> 00:01:46,240 Speaker 1: we can think of vibration as energy. So this energy 25 00:01:46,319 --> 00:01:50,840 Speaker 1: needs a medium to travel through. Sound travels through matter, 26 00:01:51,320 --> 00:01:54,200 Speaker 1: and it doesn't matter if the matter is solid, liquid, 27 00:01:54,480 --> 00:01:57,720 Speaker 1: or gas. It can travel through it, but it definitely 28 00:01:57,800 --> 00:02:00,480 Speaker 1: needs to have a medium in order to try. This 29 00:02:00,560 --> 00:02:03,520 Speaker 1: is why out in space there is no sound. You know, 30 00:02:03,760 --> 00:02:06,480 Speaker 1: in space, no one can hear you scream. Well, that's 31 00:02:06,520 --> 00:02:10,560 Speaker 1: because in space you have these vast regions where there 32 00:02:10,600 --> 00:02:15,200 Speaker 1: is so little matter out there that sound cannot pass 33 00:02:15,520 --> 00:02:19,480 Speaker 1: through it. There's nothing for the sound to transfer energy to. 34 00:02:19,960 --> 00:02:22,240 Speaker 1: So it's not just that it's a lack of air, 35 00:02:22,480 --> 00:02:25,240 Speaker 1: it's that it's a lack of anything, or at least 36 00:02:25,520 --> 00:02:29,160 Speaker 1: there's not enough significant amount of anything out there that 37 00:02:29,200 --> 00:02:32,839 Speaker 1: would allow for the transfer of longitudinal waves. By the way, 38 00:02:32,880 --> 00:02:36,840 Speaker 1: that's how sound travels. Sound travels in longitudinal waves. So 39 00:02:37,040 --> 00:02:40,239 Speaker 1: broadly speaking, there are two types of waves. There's longitudinal 40 00:02:40,480 --> 00:02:44,080 Speaker 1: and there's transverse. Transverse waves are what I think a 41 00:02:44,120 --> 00:02:47,680 Speaker 1: lot of folks imagine when they think of waves, often 42 00:02:47,720 --> 00:02:50,400 Speaker 1: it's how we plot waves on a chart. It's a 43 00:02:50,480 --> 00:02:53,160 Speaker 1: very easy way of doing it. So one way you 44 00:02:53,200 --> 00:02:57,680 Speaker 1: could actually see transverse waves in action is just with 45 00:02:57,760 --> 00:03:00,720 Speaker 1: a length of rope, a nice long length of The 46 00:03:00,800 --> 00:03:03,440 Speaker 1: longer the better, really, because it's easier to see. And 47 00:03:03,600 --> 00:03:05,560 Speaker 1: if you had a long length of rope and you 48 00:03:05,639 --> 00:03:08,320 Speaker 1: picked up just one end of it, it's laid out 49 00:03:08,400 --> 00:03:11,120 Speaker 1: straight in front of you. Then you started to move 50 00:03:11,200 --> 00:03:14,320 Speaker 1: the end of the rope from side to side, left 51 00:03:14,320 --> 00:03:17,000 Speaker 1: to right back again, over and over again. You would 52 00:03:17,040 --> 00:03:21,520 Speaker 1: see waves traveled down the length of the rope. But 53 00:03:21,639 --> 00:03:24,520 Speaker 1: this means that the wave is traveling at like a 54 00:03:24,639 --> 00:03:29,480 Speaker 1: ninety degree angle from the disturbance of the medium, because 55 00:03:29,520 --> 00:03:32,880 Speaker 1: again you're moving the rope left and right. You're not 56 00:03:33,080 --> 00:03:35,880 Speaker 1: pushing on the rope. You're moving the rope left and right, 57 00:03:35,880 --> 00:03:38,760 Speaker 1: but the waves are traveling down the rope. By the way, 58 00:03:38,800 --> 00:03:40,880 Speaker 1: the same thing would happen if you were moving the 59 00:03:41,200 --> 00:03:43,960 Speaker 1: rope up and down right. If you moved them up 60 00:03:43,960 --> 00:03:46,680 Speaker 1: and down, you would still see the disturbance happening up 61 00:03:46,680 --> 00:03:49,320 Speaker 1: and down, but the direction of the waves travel would 62 00:03:49,360 --> 00:03:53,080 Speaker 1: be forward down the length of rope. Now, a longitudinal 63 00:03:53,160 --> 00:03:57,800 Speaker 1: wave is different. The wave travels in the same direction 64 00:03:58,280 --> 00:04:02,080 Speaker 1: as the disturbance rather at a ninety degree angle from it. 65 00:04:02,200 --> 00:04:04,800 Speaker 1: So in this case, if the rope behaved like a 66 00:04:04,840 --> 00:04:08,160 Speaker 1: longitudinal wave, if you pushed on the end of the rope, 67 00:04:08,480 --> 00:04:12,520 Speaker 1: you would see the disturbance and wave traveled down the length. 68 00:04:12,640 --> 00:04:15,400 Speaker 1: But that doesn't happen with rope. However, it does happen 69 00:04:15,680 --> 00:04:19,560 Speaker 1: with one of the most important tools in any serious 70 00:04:19,800 --> 00:04:24,640 Speaker 1: scientist's tool box. I'm talking about a slinky for fun. 71 00:04:25,160 --> 00:04:27,920 Speaker 1: It's a wonderful toy. So if you take a slinky 72 00:04:28,320 --> 00:04:30,720 Speaker 1: and you stretch it out a little bit between two people, 73 00:04:30,960 --> 00:04:32,960 Speaker 1: and then you ask one of those two people to 74 00:04:33,640 --> 00:04:36,760 Speaker 1: push the slinky forward really quickly, you would observe that 75 00:04:36,960 --> 00:04:40,600 Speaker 1: you would see a wave travel forward through the slinky 76 00:04:40,839 --> 00:04:44,000 Speaker 1: in the direction of the push. Areas of the slinky 77 00:04:44,160 --> 00:04:48,600 Speaker 1: would compress as this wave travels down, and in fact, 78 00:04:48,800 --> 00:04:52,240 Speaker 1: in the longitudinal wave business, we would call that compression. 79 00:04:52,600 --> 00:04:56,040 Speaker 1: Areas where the slinky links would be further apart as 80 00:04:56,080 --> 00:04:58,880 Speaker 1: the wave would travel through the medium, we would call 81 00:04:58,960 --> 00:05:03,400 Speaker 1: that rare faction. So you have rare faction and compression. 82 00:05:04,040 --> 00:05:07,520 Speaker 1: Now for the purposes of illustration, we often will draw 83 00:05:07,720 --> 00:05:11,479 Speaker 1: sound waves almost as if they were transverse waves. It's 84 00:05:11,520 --> 00:05:15,000 Speaker 1: just easier to see the parts of a wave that way. 85 00:05:15,360 --> 00:05:17,840 Speaker 1: So if we did that, if we had like your 86 00:05:18,080 --> 00:05:21,279 Speaker 1: your regular little graph, and we had a sound wave 87 00:05:21,440 --> 00:05:25,719 Speaker 1: drawn on there, similar to a transverse wave, you would 88 00:05:25,760 --> 00:05:29,040 Speaker 1: have peaks and you would have valleys, right, because that's 89 00:05:29,080 --> 00:05:33,040 Speaker 1: the way we envision these, these transverse waves. And it's 90 00:05:33,080 --> 00:05:36,280 Speaker 1: pretty simple to see a single wavelength, you know. You 91 00:05:36,360 --> 00:05:40,440 Speaker 1: just go from one peak to the following peak. That's 92 00:05:40,520 --> 00:05:44,159 Speaker 1: one wavelength. And it's not too hard to understand stuff 93 00:05:44,279 --> 00:05:49,640 Speaker 1: like amplitude and frequency. So amplitude describes how high those 94 00:05:49,640 --> 00:05:52,320 Speaker 1: peaks are from the center line, or how low the 95 00:05:52,360 --> 00:05:55,120 Speaker 1: troughs are, if you will, And we would say that 96 00:05:55,160 --> 00:05:59,480 Speaker 1: this correlates to volume with sound waves. Frequency would be 97 00:05:59,760 --> 00:06:03,320 Speaker 1: how how many wavelengths are passing a given point in 98 00:06:03,400 --> 00:06:07,720 Speaker 1: a fixed amount of time. This correlates to a sound's pitch. 99 00:06:08,160 --> 00:06:11,960 Speaker 1: The higher frequencies are higher pitches. But it would be 100 00:06:12,040 --> 00:06:15,800 Speaker 1: more accurate to illustrate this as a longitudinal wave, because 101 00:06:15,800 --> 00:06:20,280 Speaker 1: that's how sound travels. Wavelengths and longitudinal waves refer to 102 00:06:20,320 --> 00:06:23,640 Speaker 1: the distance between say one point of compression to the 103 00:06:23,680 --> 00:06:27,480 Speaker 1: next point of compression, or we could actually measure it 104 00:06:27,520 --> 00:06:30,919 Speaker 1: from one point of rarefaction to the next point of 105 00:06:31,000 --> 00:06:34,640 Speaker 1: rare affection. That would still be a wavelength. Frequency is 106 00:06:34,839 --> 00:06:39,000 Speaker 1: fairly simple. It's the number of compressions or rare factions, 107 00:06:39,000 --> 00:06:41,719 Speaker 1: depending on which one you're starting with. In other words, 108 00:06:41,800 --> 00:06:45,279 Speaker 1: the number of wavelengths that pass a given point in 109 00:06:45,320 --> 00:06:48,919 Speaker 1: a fixed amount of time. Amplitude is a little bit different. 110 00:06:49,279 --> 00:06:54,000 Speaker 1: It's the distance between points of compression within the sound wave. 111 00:06:54,400 --> 00:06:57,279 Speaker 1: If a sound wave has many points of compression that 112 00:06:57,320 --> 00:07:01,040 Speaker 1: are close to one another, it's high amplitude a loud sound. 113 00:07:01,360 --> 00:07:04,320 Speaker 1: If there's a wave that has fewer points of compression 114 00:07:04,320 --> 00:07:06,520 Speaker 1: and that maybe they're a little further apart from each other, 115 00:07:06,760 --> 00:07:11,440 Speaker 1: it's low amplitude. Its lower volume. So with sound, we 116 00:07:11,520 --> 00:07:16,080 Speaker 1: have something that's causing a vibration, and it could be anything, right. 117 00:07:16,120 --> 00:07:19,200 Speaker 1: It could be a tree following in the forest as 118 00:07:19,240 --> 00:07:21,520 Speaker 1: long as someone's there to hear it. It might be 119 00:07:21,560 --> 00:07:23,840 Speaker 1: a flower pot falling on the pavement. It could be 120 00:07:23,880 --> 00:07:27,680 Speaker 1: a fiddler drawing a bow across violin strings. It might 121 00:07:27,720 --> 00:07:31,080 Speaker 1: be a mine being tortured. It could be anything. The 122 00:07:31,200 --> 00:07:34,600 Speaker 1: sound travels out in all directions from the source, and 123 00:07:34,640 --> 00:07:38,200 Speaker 1: it travels through whatever medium it's in. The sound most 124 00:07:38,200 --> 00:07:40,760 Speaker 1: of us encounter most of the time is traveling through air, 125 00:07:40,920 --> 00:07:44,640 Speaker 1: but this also works underwater or even through solid matter. Now, 126 00:07:44,640 --> 00:07:47,720 Speaker 1: if these vibrations fall within the range of human hearing, 127 00:07:48,160 --> 00:07:50,920 Speaker 1: then we might very well hear them, as long as 128 00:07:50,960 --> 00:07:53,200 Speaker 1: we're close enough for those vibrations to get to us 129 00:07:53,480 --> 00:07:56,640 Speaker 1: before they peter out. That's called attenuation. By the way, 130 00:07:56,920 --> 00:08:00,840 Speaker 1: the sound attenuates as it travels from its source, That 131 00:08:00,960 --> 00:08:05,040 Speaker 1: means it gets weaker as it travels out further from 132 00:08:05,080 --> 00:08:07,880 Speaker 1: the source of sound, which makes sense right. Otherwise we 133 00:08:07,880 --> 00:08:10,240 Speaker 1: wouldn't be able to hear anything. Everything would just be 134 00:08:10,320 --> 00:08:13,440 Speaker 1: equally loud to us all the time, or it would 135 00:08:13,440 --> 00:08:16,640 Speaker 1: be of the same amplitude as the original sound was 136 00:08:16,880 --> 00:08:19,840 Speaker 1: and we'd all be deafened by it. So yeah, sound 137 00:08:20,440 --> 00:08:24,760 Speaker 1: diminishes in strength as it travels. Now, the range of 138 00:08:25,240 --> 00:08:30,040 Speaker 1: typical human hearing falls between twenty hurts or twenty vibrations 139 00:08:30,040 --> 00:08:34,400 Speaker 1: per second up to twenty killer hurts or twenty thousand 140 00:08:34,559 --> 00:08:38,680 Speaker 1: vibrations per second. Now, as I mentioned earlier, the lower 141 00:08:38,720 --> 00:08:43,959 Speaker 1: frequencies have lower pitches, So a twenty hurtz sound would 142 00:08:43,960 --> 00:08:47,160 Speaker 1: be a very deep bass sound. In fact, some of 143 00:08:47,200 --> 00:08:51,240 Speaker 1: those you might feel more than you hear them, depending 144 00:08:51,320 --> 00:08:54,600 Speaker 1: upon your hearing, and as we get older, we typically 145 00:08:54,600 --> 00:08:57,440 Speaker 1: lose some of the ability to hear the higher pitches. 146 00:08:57,640 --> 00:09:00,080 Speaker 1: I think the last hearing test I did said my 147 00:09:00,120 --> 00:09:03,640 Speaker 1: hearing kind of tops out around fifteen or sixteen killer hurtz, 148 00:09:04,000 --> 00:09:07,480 Speaker 1: So thatre's a lot of space between the upper limits 149 00:09:07,520 --> 00:09:10,840 Speaker 1: of my hearing and the typical range for human hearing. 150 00:09:11,080 --> 00:09:13,319 Speaker 1: Part of that is just because I'm old, and part 151 00:09:13,360 --> 00:09:15,280 Speaker 1: of that is also because I saw a lot of 152 00:09:15,360 --> 00:09:19,200 Speaker 1: rock concerts or rock shows. I can't call them concerts 153 00:09:19,280 --> 00:09:22,280 Speaker 1: rock shows when I was in college, thanks to Dick 154 00:09:22,400 --> 00:09:25,200 Speaker 1: Dale and the Dell Tones and the Hate Bombs and 155 00:09:25,240 --> 00:09:28,200 Speaker 1: the Woggles and all the other bands I saw that 156 00:09:28,280 --> 00:09:30,720 Speaker 1: ruined my hearing. It's really my fault. I should have 157 00:09:30,720 --> 00:09:35,520 Speaker 1: worn earplugs anyway. Younger people can still hear those higher 158 00:09:35,520 --> 00:09:38,559 Speaker 1: frequencies typically. I mean we always have to say typically, 159 00:09:38,559 --> 00:09:41,680 Speaker 1: because there are obviously exceptions. But you may have heard 160 00:09:41,720 --> 00:09:45,280 Speaker 1: that some businesses have even installed speakers that would play very, 161 00:09:45,920 --> 00:09:49,920 Speaker 1: very high pitched sounds in order to discourage youngsters from 162 00:09:50,160 --> 00:09:54,040 Speaker 1: loitering at that place of business, Like convenience stores and stuff, 163 00:09:54,200 --> 00:09:57,000 Speaker 1: so the adults could shop in peace, and all those young, 164 00:09:57,160 --> 00:10:00,520 Speaker 1: unruly hooligans would be chased out by unpleas a high 165 00:10:00,600 --> 00:10:03,559 Speaker 1: pitched noise. I did a cursory search on this and 166 00:10:03,559 --> 00:10:08,079 Speaker 1: found devices that are called mosquito alarms. These alarms push 167 00:10:08,080 --> 00:10:11,760 Speaker 1: out sound at high amplitude. But if you're like me 168 00:10:12,360 --> 00:10:16,320 Speaker 1: and you've lost hearing in those frequency ranges, well it 169 00:10:16,400 --> 00:10:19,120 Speaker 1: don't bug you none. You don't hear it even though 170 00:10:19,160 --> 00:10:21,920 Speaker 1: it's being played at high volume. But meanwhile, all the 171 00:10:21,960 --> 00:10:24,880 Speaker 1: little tykes grab their ears and run off, and it 172 00:10:24,960 --> 00:10:27,880 Speaker 1: leaves me to buy my slim gems in peace. I'm 173 00:10:27,880 --> 00:10:31,000 Speaker 1: mostly kidding about that. I'm not that grouchy. I'm not 174 00:10:31,040 --> 00:10:36,360 Speaker 1: really a fan of making spaces inherently unwelcome to slices 175 00:10:36,360 --> 00:10:39,800 Speaker 1: of demographics. Also, I don't eat slim gems. Apologies to 176 00:10:39,920 --> 00:10:44,760 Speaker 1: Randy Savage. Anyway. Let's talk about the perception of sound. 177 00:10:45,080 --> 00:10:49,359 Speaker 1: So when sound waves enter our ears, the wave travels 178 00:10:49,559 --> 00:10:52,400 Speaker 1: to the tympanic membrane, which is also known as the 179 00:10:52,440 --> 00:10:56,559 Speaker 1: ear drum. So the sound wave transfers vibrations to this membrane, 180 00:10:56,600 --> 00:10:59,280 Speaker 1: and it's actually doing that through very small changes in 181 00:10:59,360 --> 00:11:03,120 Speaker 1: air pressure in our ear canals, so these small changes 182 00:11:03,160 --> 00:11:07,520 Speaker 1: in air pressure are essentially pushing and pulling against that membrane. Now, 183 00:11:07,520 --> 00:11:11,680 Speaker 1: the membrane in turn transfers those vibrations to three very 184 00:11:11,880 --> 00:11:15,600 Speaker 1: tiny delicate bones in our middle ears. Those are the hammer, 185 00:11:15,760 --> 00:11:18,440 Speaker 1: the anvil, and the stirrup, and they're called that because 186 00:11:18,440 --> 00:11:20,760 Speaker 1: that's kind of what they look like. And these tiny 187 00:11:20,800 --> 00:11:25,000 Speaker 1: bones kind of act like an amplifier, and they send 188 00:11:25,040 --> 00:11:28,880 Speaker 1: the vibrations further along into the inner ear, where a 189 00:11:29,240 --> 00:11:33,839 Speaker 1: snail shaped structure called the cochlea sits. Now, the cochlea 190 00:11:34,160 --> 00:11:38,280 Speaker 1: contains fluid within it, and the vibrations to the cochlea 191 00:11:38,360 --> 00:11:41,880 Speaker 1: make this fluid ripple. This in turn creates a wave 192 00:11:42,040 --> 00:11:45,120 Speaker 1: on the membrane that lines the cochlea. And there are 193 00:11:45,160 --> 00:11:50,280 Speaker 1: these little hair like protrusions inside the cochlea. They're called stereocilia. 194 00:11:50,760 --> 00:11:55,840 Speaker 1: They vibrate from all this rippling, and they transfer those vibrations, 195 00:11:55,880 --> 00:12:00,600 Speaker 1: this physical vibration into electrical impulses. Those impulse is then 196 00:12:00,679 --> 00:12:04,400 Speaker 1: travel to our brains and the brain interprets the these 197 00:12:04,440 --> 00:12:08,679 Speaker 1: a sound. So ultimately the sounds we encounter are in 198 00:12:08,720 --> 00:12:12,240 Speaker 1: a sense all in our heads. Thus the question if 199 00:12:12,280 --> 00:12:14,480 Speaker 1: a tree falls in the forest and no one is 200 00:12:14,520 --> 00:12:16,640 Speaker 1: there to hear it, does it make a sound? You 201 00:12:16,679 --> 00:12:20,680 Speaker 1: could argue, really, sound only exists within the mind, and 202 00:12:20,720 --> 00:12:23,080 Speaker 1: if there is no mind to perceive it, there is 203 00:12:23,160 --> 00:12:27,080 Speaker 1: no sound. Our brains create the perception of that sound. 204 00:12:27,400 --> 00:12:31,240 Speaker 1: So this raises a question, is what we hear actually 205 00:12:31,440 --> 00:12:34,800 Speaker 1: what is happening out in reality? If somehow we were 206 00:12:34,840 --> 00:12:38,720 Speaker 1: able to step outside of the experience of being human 207 00:12:39,040 --> 00:12:43,800 Speaker 1: and to perceive things as they truly are, would sounds 208 00:12:44,000 --> 00:12:47,960 Speaker 1: appear to be anything like what we perceive. Now that's 209 00:12:48,000 --> 00:12:51,160 Speaker 1: a question for philosophers, but you know, it sure would 210 00:12:51,200 --> 00:12:54,000 Speaker 1: be interesting if we found out that every single person's 211 00:12:54,040 --> 00:12:59,439 Speaker 1: experiences sound differently like. It's just that collectively we all 212 00:12:59,480 --> 00:13:02,600 Speaker 1: agree that the thing causing the sound is awesome, like 213 00:13:02,679 --> 00:13:05,480 Speaker 1: maybe a new they might be Giant's song, or that 214 00:13:05,559 --> 00:13:09,120 Speaker 1: it's awful like a new kid rock song. Just having 215 00:13:09,160 --> 00:13:12,400 Speaker 1: fun here, But no, Seriously, because it's impossible for us 216 00:13:12,480 --> 00:13:15,520 Speaker 1: to step into the experience of someone else, we can't 217 00:13:15,600 --> 00:13:18,920 Speaker 1: really be sure that the way we experience sound is 218 00:13:18,960 --> 00:13:22,520 Speaker 1: the same as what other people experience kind of the 219 00:13:22,559 --> 00:13:24,440 Speaker 1: same way. That there's no way for me to know 220 00:13:24,880 --> 00:13:27,160 Speaker 1: if the shade of blue I see when I look 221 00:13:27,200 --> 00:13:30,000 Speaker 1: in the sky is the same experience you have when 222 00:13:30,040 --> 00:13:32,520 Speaker 1: you do the same thing. Now, I know I'm getting 223 00:13:32,559 --> 00:13:36,800 Speaker 1: a little bit whibbly wobbly here, But acoustics, the science 224 00:13:37,160 --> 00:13:41,400 Speaker 1: of sound involves a lot of psychology. If you listen 225 00:13:41,440 --> 00:13:44,200 Speaker 1: to my episodes about the MP three format, you know 226 00:13:44,320 --> 00:13:48,440 Speaker 1: that one way MP three's can serve filespace is the 227 00:13:48,480 --> 00:13:53,720 Speaker 1: compression algorithm ditches any sounds deemed to be beyond human perception. 228 00:13:54,000 --> 00:13:57,040 Speaker 1: Like if a very quiet sound follows a very loud sound, 229 00:13:57,280 --> 00:13:59,880 Speaker 1: typically we can't hear the quiet one. The loud one 230 00:14:00,200 --> 00:14:02,480 Speaker 1: as almost kind of deadened ust to being able to 231 00:14:02,520 --> 00:14:04,520 Speaker 1: hear the quiet one. And I'm talking about like these 232 00:14:04,559 --> 00:14:07,120 Speaker 1: sounds are like back to back one raft or the other. 233 00:14:07,400 --> 00:14:10,880 Speaker 1: So the compression algorithm would say, oh, well, no one's 234 00:14:10,920 --> 00:14:12,520 Speaker 1: going to be able to hear the second sound in 235 00:14:12,559 --> 00:14:14,600 Speaker 1: the first place, so why would be encode it? Just 236 00:14:14,679 --> 00:14:18,360 Speaker 1: leave it out, and thus it conserves filespace. Of course, 237 00:14:18,360 --> 00:14:20,960 Speaker 1: if you start to ditch stuff humans actually can perceive, 238 00:14:21,160 --> 00:14:23,480 Speaker 1: you begin to affect the quality of sound, and then 239 00:14:23,520 --> 00:14:27,240 Speaker 1: you have problems with the decline and quality. All right, 240 00:14:27,560 --> 00:14:30,320 Speaker 1: I've got tons more to say, and Obviously, we haven't 241 00:14:30,320 --> 00:14:33,080 Speaker 1: even gotten to active noise cancelation yet, So let's take 242 00:14:33,120 --> 00:14:44,640 Speaker 1: a quick break and we'll be right back. Okay, we're back, 243 00:14:44,680 --> 00:14:48,520 Speaker 1: and we're going back to sound waves. So you might 244 00:14:48,600 --> 00:14:53,120 Speaker 1: recall that the speed of light is constant, which is 245 00:14:53,560 --> 00:14:56,960 Speaker 1: kind of true, but not all the truth. The speed 246 00:14:56,960 --> 00:15:00,920 Speaker 1: of light is constant given the medium through which it travels. 247 00:15:01,240 --> 00:15:04,800 Speaker 1: When light from the Sun reaches Earth, it actually slows 248 00:15:04,880 --> 00:15:08,040 Speaker 1: down a little bit as that light hits our atmosphere. 249 00:15:08,200 --> 00:15:11,040 Speaker 1: And by a little bit, I mean a very small amount, 250 00:15:11,120 --> 00:15:15,320 Speaker 1: small enough to be deemed insignificant based upon like the 251 00:15:15,400 --> 00:15:17,880 Speaker 1: speed it travels through a vacuum versus the speed it 252 00:15:17,920 --> 00:15:21,920 Speaker 1: travels through air, insignificant for most calculations. I mean, it 253 00:15:21,960 --> 00:15:25,200 Speaker 1: does happen, but it's a very tiny change. The ratio 254 00:15:25,200 --> 00:15:27,600 Speaker 1: of difference between the faster and slower rates is called 255 00:15:27,640 --> 00:15:30,960 Speaker 1: the refractive index. I'm getting a little off topic, although 256 00:15:30,960 --> 00:15:33,800 Speaker 1: the same thing kind of happens with sound too, But sound, 257 00:15:34,080 --> 00:15:38,080 Speaker 1: like light, will travel at different speeds depending upon the 258 00:15:38,120 --> 00:15:42,880 Speaker 1: medium through which it travels. Moreover, the temperature of the 259 00:15:43,000 --> 00:15:46,800 Speaker 1: medium will affect how fast sound is able to travel 260 00:15:46,840 --> 00:15:51,000 Speaker 1: through it. Sound travels faster through hot air than it 261 00:15:51,040 --> 00:15:54,080 Speaker 1: does through cold air. Now, when you think about it, 262 00:15:54,160 --> 00:15:59,520 Speaker 1: that makes sense. Sound is vibration. Hot air has molecules 263 00:15:59,520 --> 00:16:02,880 Speaker 1: and atom They have more energy in them, so they're 264 00:16:02,920 --> 00:16:06,560 Speaker 1: more inclined to vibrate. They're already moving around. They'll carry 265 00:16:06,640 --> 00:16:10,280 Speaker 1: movement more easily than cold air does because cold air 266 00:16:10,520 --> 00:16:14,520 Speaker 1: has less energy in it, so the vibrations come less readily. 267 00:16:14,840 --> 00:16:17,840 Speaker 1: This gets reflected in the speed of sound. Sound traveling 268 00:16:17,840 --> 00:16:20,920 Speaker 1: on a day that's around sixty degrees fahrenheit, we'll move 269 00:16:20,960 --> 00:16:24,720 Speaker 1: it about two and twenty kilometers per hour. But let's 270 00:16:24,720 --> 00:16:28,440 Speaker 1: say it's a really chilly night, like negative sixty seven 271 00:16:28,520 --> 00:16:31,600 Speaker 1: degrees fahrenheit. Then you're talking about sound travel I get 272 00:16:31,640 --> 00:16:35,320 Speaker 1: around one than fifty six kilometers per hour. Though, you know, 273 00:16:35,360 --> 00:16:37,640 Speaker 1: if you're out in weather that's that cold, the speed 274 00:16:37,640 --> 00:16:40,160 Speaker 1: of sound probably isn't is you know, not top of 275 00:16:40,280 --> 00:16:43,200 Speaker 1: mind to you. You're probably thinking, how do I get 276 00:16:43,240 --> 00:16:46,040 Speaker 1: inside before I freeze to death. Now let's get back 277 00:16:46,080 --> 00:16:49,680 Speaker 1: to sound waves in order to understand how noise cancelation 278 00:16:49,840 --> 00:16:53,320 Speaker 1: actually works. All right, So I mentioned earlier. Sound waves 279 00:16:53,560 --> 00:16:57,200 Speaker 1: have wavelengths, and we describe the frequency of sound by 280 00:16:57,240 --> 00:17:00,680 Speaker 1: the number of wavelengths that pass a fixed point in 281 00:17:00,800 --> 00:17:04,000 Speaker 1: space within a given amount of time. So if we're 282 00:17:04,040 --> 00:17:07,280 Speaker 1: using hurts as our measurement, the amount of time is 283 00:17:07,400 --> 00:17:10,240 Speaker 1: one second. So let's say that you are able to 284 00:17:10,359 --> 00:17:13,600 Speaker 1: see sound waves and you're able to count really fast, 285 00:17:13,720 --> 00:17:16,439 Speaker 1: like time to you doesn't pass the same way it 286 00:17:16,480 --> 00:17:20,240 Speaker 1: does to everybody else, and you use a stop watch 287 00:17:20,440 --> 00:17:23,440 Speaker 1: so that you can click down a single second. Meanwhile, 288 00:17:23,560 --> 00:17:27,000 Speaker 1: you're counting all the sound waves that go past you. Well, 289 00:17:27,320 --> 00:17:29,359 Speaker 1: if you did that, the number you would come up 290 00:17:29,400 --> 00:17:33,159 Speaker 1: to that would be the sound's frequency. In hurts, the 291 00:17:33,200 --> 00:17:36,280 Speaker 1: amount of time it takes just one wavelength to pass 292 00:17:36,359 --> 00:17:39,760 Speaker 1: a fixed point is called a period. So for a 293 00:17:39,880 --> 00:17:44,399 Speaker 1: twenty Hurtz sound, a period is just one twentieth of 294 00:17:44,480 --> 00:17:47,119 Speaker 1: a second. That's how long it would take a single 295 00:17:47,160 --> 00:17:50,560 Speaker 1: wavelength to complete one cycle. So if we were to 296 00:17:50,760 --> 00:17:54,760 Speaker 1: further divide that period into even smaller fractions, we could 297 00:17:54,760 --> 00:17:58,600 Speaker 1: call those phases. To get into phases in detail would 298 00:17:58,640 --> 00:18:01,960 Speaker 1: really require visual aid, because otherwise I would just start 299 00:18:02,000 --> 00:18:04,640 Speaker 1: spouting off formula to you and it would all get 300 00:18:04,760 --> 00:18:08,840 Speaker 1: very confusing for me. Really. I mean, you might be fine, 301 00:18:09,200 --> 00:18:11,919 Speaker 1: but I would inevitably say something wrong. So I'm not 302 00:18:11,960 --> 00:18:14,800 Speaker 1: even gonna bother doing it because I'll just mess it up. 303 00:18:15,119 --> 00:18:18,320 Speaker 1: But if you have two or more waves, and let's 304 00:18:18,359 --> 00:18:20,280 Speaker 1: say all of these waves, these are sound waves, they 305 00:18:20,280 --> 00:18:23,760 Speaker 1: are longitudinal. So let's say all these waves are aligned 306 00:18:23,840 --> 00:18:27,119 Speaker 1: in that they have the same areas of compression and rarefaction. 307 00:18:27,520 --> 00:18:30,600 Speaker 1: As they travel past a fixed point, those sound waves 308 00:18:30,600 --> 00:18:33,560 Speaker 1: would be said to be in phase with one another. 309 00:18:34,080 --> 00:18:37,720 Speaker 1: They're all kind of traveling at the same speed in 310 00:18:37,800 --> 00:18:41,280 Speaker 1: the same direction. But let's say you have sound wave 311 00:18:41,359 --> 00:18:44,600 Speaker 1: A and it travels with its various compression and rare 312 00:18:44,640 --> 00:18:48,560 Speaker 1: faction zones, and then you've got sound wave B. But 313 00:18:48,760 --> 00:18:54,159 Speaker 1: soundwave b's compression zones are matching with a's rarefaction zones, 314 00:18:54,440 --> 00:18:58,200 Speaker 1: and b's rarefaction zones are matching with a's compression zones. 315 00:18:58,280 --> 00:19:01,159 Speaker 1: So they're opposite. They're like the opposite sides of a 316 00:19:01,200 --> 00:19:04,840 Speaker 1: puzzle fitting in together. And let's say they match each 317 00:19:04,840 --> 00:19:08,200 Speaker 1: other in amplitude, so they're both the same volume. Well 318 00:19:08,200 --> 00:19:11,560 Speaker 1: what happens at that point, Well, what happens is they 319 00:19:11,640 --> 00:19:17,639 Speaker 1: cancel each other out. It's called destructive interference. Essentially, it 320 00:19:17,680 --> 00:19:20,359 Speaker 1: all comes down to math. If we were to assign 321 00:19:20,600 --> 00:19:25,000 Speaker 1: values to these waves, then maybe we say wave A 322 00:19:25,520 --> 00:19:29,560 Speaker 1: is at value two at a given point, while wave 323 00:19:29,640 --> 00:19:32,640 Speaker 1: B is at negative two. So then we add these 324 00:19:32,640 --> 00:19:36,280 Speaker 1: two together two plus negative two equals zero. Now that 325 00:19:36,400 --> 00:19:39,560 Speaker 1: is an oversimplification of what's going on here, but it's 326 00:19:40,000 --> 00:19:44,320 Speaker 1: basically the concept behind noise cancelation. Now, if we think 327 00:19:44,359 --> 00:19:47,840 Speaker 1: of transverse waves, which I think are easier to imagine, 328 00:19:48,000 --> 00:19:50,920 Speaker 1: this would be like having two waves where the peaks 329 00:19:51,160 --> 00:19:54,480 Speaker 1: of wave A are matched up with the values of 330 00:19:54,600 --> 00:19:58,760 Speaker 1: wave B and vice versa, and that the height the 331 00:19:58,800 --> 00:20:02,760 Speaker 1: amplitude of those peaks and valleys is exactly the same, 332 00:20:02,960 --> 00:20:06,680 Speaker 1: and what we get ultimately is cancelation. The two waves 333 00:20:06,840 --> 00:20:09,400 Speaker 1: sound waves in this case, eliminate each other and we 334 00:20:09,440 --> 00:20:12,960 Speaker 1: hear nothing as a result. Or if you prefer those 335 00:20:13,040 --> 00:20:16,440 Speaker 1: differences in air pressure that happens in our ear canals 336 00:20:16,480 --> 00:20:20,439 Speaker 1: that ultimately we end up perceiving as sound. Those differences 337 00:20:20,560 --> 00:20:25,440 Speaker 1: never happen because while one sound wave is pushing one way, 338 00:20:25,800 --> 00:20:28,520 Speaker 1: the other sound wave is pushing the other way with 339 00:20:28,680 --> 00:20:32,119 Speaker 1: equal force, and the air particles don't do anything, they 340 00:20:32,160 --> 00:20:36,000 Speaker 1: don't go anywhere, So therefore we hear nothing. But getting 341 00:20:36,040 --> 00:20:39,520 Speaker 1: to that point where we could actually create technology that 342 00:20:39,560 --> 00:20:43,879 Speaker 1: could detect incoming sound and then produce out of phase 343 00:20:44,080 --> 00:20:48,000 Speaker 1: equivalence for the purposes of eliminating that sound. That would 344 00:20:48,040 --> 00:20:51,479 Speaker 1: take a lot of time, the better part of a 345 00:20:51,560 --> 00:20:56,399 Speaker 1: century actually now. One person who suggested an approach to 346 00:20:56,440 --> 00:21:00,159 Speaker 1: do this was a doctor of philosophy and medicine in 347 00:21:00,200 --> 00:21:04,560 Speaker 1: Germany back in the nineteen thirties. His name was Paul Lug, 348 00:21:05,040 --> 00:21:08,720 Speaker 1: and he applied for a patent that he titled process 349 00:21:08,960 --> 00:21:14,320 Speaker 1: of Silencing Sound Oscillations. Now, the patent application begins by 350 00:21:14,359 --> 00:21:17,639 Speaker 1: explaining that up to that point, the only way to 351 00:21:17,680 --> 00:21:22,280 Speaker 1: cancel displeasing oscillations was to build in mechanical solutions at 352 00:21:22,320 --> 00:21:26,639 Speaker 1: the source of the noise itself. His invention would allow 353 00:21:26,680 --> 00:21:31,280 Speaker 1: for the installation of noise canceling technology that was independent 354 00:21:31,880 --> 00:21:35,600 Speaker 1: of the source of the noise. So, instead of trying 355 00:21:35,600 --> 00:21:38,320 Speaker 1: to figure out a way to mechanically alter a process 356 00:21:38,560 --> 00:21:41,680 Speaker 1: so that it produced less noise, you could use Lug's 357 00:21:41,760 --> 00:21:45,240 Speaker 1: invention to eliminate noise no matter where it came from, 358 00:21:45,560 --> 00:21:49,440 Speaker 1: because this device would be able to take in incoming 359 00:21:49,480 --> 00:21:54,199 Speaker 1: noise and produce the anti phase version of it. He 360 00:21:54,280 --> 00:21:58,239 Speaker 1: described the basic components of noise cancelation, and in his 361 00:21:58,320 --> 00:22:03,520 Speaker 1: description he mentioned microphones or receivers which would detect incoming 362 00:22:03,560 --> 00:22:08,680 Speaker 1: sound waves and a quote unquote reproducing apparatus. In other words, 363 00:22:08,760 --> 00:22:12,000 Speaker 1: essentially a loud speaker of some sort that would produce 364 00:22:12,119 --> 00:22:15,199 Speaker 1: sounds having an opposite phase to the incoming noise. The 365 00:22:15,280 --> 00:22:18,160 Speaker 1: opposing phase sound waves would then cancel each other out. 366 00:22:18,680 --> 00:22:22,240 Speaker 1: Lug also mentioned ways to eliminate only part of a 367 00:22:22,320 --> 00:22:26,520 Speaker 1: noise or only specific types of noises. So he thought 368 00:22:26,600 --> 00:22:29,200 Speaker 1: this would be handy if you needed to eliminate noises 369 00:22:29,240 --> 00:22:32,199 Speaker 1: and loud environments while still allowing people to speak with 370 00:22:32,240 --> 00:22:35,080 Speaker 1: one another. So how do you eliminate noise but you 371 00:22:35,240 --> 00:22:38,679 Speaker 1: allow signal to get through? That was what he was 372 00:22:38,720 --> 00:22:41,960 Speaker 1: talking about. He was also thinking about ways to eliminate 373 00:22:42,160 --> 00:22:45,800 Speaker 1: unwanted noises in places like say a theater or a 374 00:22:45,880 --> 00:22:49,040 Speaker 1: concert hall, where maybe you go to the concert hall 375 00:22:49,400 --> 00:22:52,800 Speaker 1: and the music is fantastic, but there's some element, some 376 00:22:53,119 --> 00:22:58,120 Speaker 1: acoustic element in that environment. This is producing something that 377 00:22:58,359 --> 00:23:02,639 Speaker 1: was not wanted, that is detracting from the experience of 378 00:23:02,720 --> 00:23:06,960 Speaker 1: hearing this concert. Luke said, well, we could create this 379 00:23:07,280 --> 00:23:12,600 Speaker 1: technology that would detect this unwanted frequency, like we would 380 00:23:12,680 --> 00:23:16,159 Speaker 1: tune it to that and then produce the anti phase 381 00:23:16,240 --> 00:23:19,360 Speaker 1: version and then you could just enjoy the concert as 382 00:23:19,400 --> 00:23:23,920 Speaker 1: it was intended, without any of these unpleasant secondary noises 383 00:23:24,040 --> 00:23:29,679 Speaker 1: mixed in. Now, Luke's idea was pretty solid. Unfortunately, the 384 00:23:29,800 --> 00:23:33,679 Speaker 1: technology was nowhere near where it needed to be in 385 00:23:33,800 --> 00:23:38,600 Speaker 1: order to actually realize his idea was He did get 386 00:23:38,600 --> 00:23:42,280 Speaker 1: his patent, he got that, granted, but he was getting 387 00:23:42,280 --> 00:23:46,720 Speaker 1: a lot of resistance in the academic world of Germany 388 00:23:46,800 --> 00:23:49,640 Speaker 1: because I think a lot of other people realized they 389 00:23:49,800 --> 00:23:53,080 Speaker 1: just couldn't accomplish what he was suggesting. Not that what 390 00:23:53,160 --> 00:23:57,479 Speaker 1: he was saying was impossible from a science perspective, but 391 00:23:57,560 --> 00:24:01,720 Speaker 1: on a technical level they couldn't figure it out. And moreover, 392 00:24:02,080 --> 00:24:05,440 Speaker 1: things in Germany were obviously getting rather tense in the 393 00:24:05,560 --> 00:24:10,520 Speaker 1: nineteen thirties as the world continued to plunge toward total 394 00:24:10,880 --> 00:24:13,560 Speaker 1: war in the region. Now I tried to find out 395 00:24:13,600 --> 00:24:17,080 Speaker 1: more information about lug and I did discover a paper 396 00:24:17,160 --> 00:24:20,080 Speaker 1: that was written in German that was all about him 397 00:24:20,240 --> 00:24:26,320 Speaker 1: and his life both before and after his proposed invention. Now, 398 00:24:26,359 --> 00:24:30,360 Speaker 1: my German is awful. I am not at all fluent, 399 00:24:30,480 --> 00:24:35,359 Speaker 1: so I depended heavily, really entirely on Google Translate, and 400 00:24:35,560 --> 00:24:39,760 Speaker 1: was only partially successful in translating the article because the 401 00:24:39,800 --> 00:24:44,120 Speaker 1: translation just wasn't fantastic. However, from what I can figure out, 402 00:24:44,240 --> 00:24:47,520 Speaker 1: Luke discovered that some engineers in England were attempting to 403 00:24:47,520 --> 00:24:50,800 Speaker 1: build an invention that was really similar to the one 404 00:24:50,880 --> 00:24:54,720 Speaker 1: he described in his pat and he suspected that someone 405 00:24:54,960 --> 00:24:59,800 Speaker 1: somewhere along the way had leaked his invention and allow 406 00:25:00,320 --> 00:25:03,119 Speaker 1: people in England to read about it and try and 407 00:25:03,200 --> 00:25:05,840 Speaker 1: create the thing that he had proposed, So he wrote 408 00:25:05,880 --> 00:25:09,040 Speaker 1: a letter to the German Patent Office demanding an explanation. 409 00:25:09,680 --> 00:25:12,320 Speaker 1: This turned out to be a bad move because the 410 00:25:12,440 --> 00:25:15,800 Speaker 1: Nazis were steadily gaining control of all of Germany's political 411 00:25:15,840 --> 00:25:18,760 Speaker 1: systems and they were not super keen to be called 412 00:25:18,840 --> 00:25:23,560 Speaker 1: into question, and they in turn decided to turn scrutiny 413 00:25:23,640 --> 00:25:27,199 Speaker 1: onto Luke, and he was reprimanded for his insolence, and 414 00:25:27,280 --> 00:25:30,280 Speaker 1: apparently he spent the next decade in fear of what 415 00:25:30,440 --> 00:25:33,160 Speaker 1: might happen to him and his family. You know, those 416 00:25:33,240 --> 00:25:36,439 Speaker 1: Nazis held a grudge. And he also couldn't get a 417 00:25:36,520 --> 00:25:39,800 Speaker 1: job as a physicist. It appeared that he had been blacklisted, 418 00:25:40,240 --> 00:25:43,119 Speaker 1: so instead he trained to be a doctor. Now, he 419 00:25:43,200 --> 00:25:46,080 Speaker 1: survived well after the war, but from what he can tell, 420 00:25:46,119 --> 00:25:50,280 Speaker 1: he never really got to work on noise cancelation again. Instead, 421 00:25:50,640 --> 00:25:52,200 Speaker 1: we're going to have to leap on over to the 422 00:25:52,280 --> 00:25:57,199 Speaker 1: nineteen fifties. An American scientist and engineer named Lawrence J. 423 00:25:57,520 --> 00:26:01,280 Speaker 1: Fogel would become a key figure in no cancelation, to 424 00:26:01,359 --> 00:26:04,159 Speaker 1: the point where many will refer to Fogel as the 425 00:26:04,240 --> 00:26:09,520 Speaker 1: inventor of active noise cancelation. I'm not sure that's entirely fair, 426 00:26:09,960 --> 00:26:14,040 Speaker 1: because you know, Lug certainly patented it back in the 427 00:26:14,119 --> 00:26:16,520 Speaker 1: nineteen thirties, but he never got it to work, Like 428 00:26:16,560 --> 00:26:19,520 Speaker 1: the technology wasn't there, So I guess you could argue 429 00:26:19,520 --> 00:26:22,560 Speaker 1: that Fogel is the inventor in the sense that Fogel 430 00:26:22,640 --> 00:26:26,840 Speaker 1: was able to create an actual working prototype of noise 431 00:26:27,119 --> 00:26:31,560 Speaker 1: reduction headphones. He had done a great deal of scientific 432 00:26:31,560 --> 00:26:34,879 Speaker 1: and practical engineering work in wave dynamics. This guy was 433 00:26:35,359 --> 00:26:40,160 Speaker 1: like super smart and studied lots of different disciplines, and 434 00:26:40,280 --> 00:26:44,320 Speaker 1: he knew a lot about wave interactions and wave interference. 435 00:26:44,760 --> 00:26:47,359 Speaker 1: He had worked in not just sound waves, but like 436 00:26:47,440 --> 00:26:53,280 Speaker 1: electromagnetic waves VHF and UHF waves, and he understood about 437 00:26:53,359 --> 00:26:56,560 Speaker 1: waves and how they perform when they are in antiphase 438 00:26:56,640 --> 00:26:59,959 Speaker 1: with one another, how that can result in destructive interference. 439 00:27:00,240 --> 00:27:02,560 Speaker 1: He also knew there was a need for better ear 440 00:27:02,600 --> 00:27:06,480 Speaker 1: protection for folks who were working in very noisy environments, 441 00:27:06,640 --> 00:27:11,359 Speaker 1: specifically in the cockpits of aircraft like helicopters and airplanes, 442 00:27:11,560 --> 00:27:14,000 Speaker 1: and he theorized that he could build a set of 443 00:27:14,040 --> 00:27:17,040 Speaker 1: headphones that could diminish or even eliminate the noise of 444 00:27:17,080 --> 00:27:20,720 Speaker 1: propeller driven aircraft so that the pilot could focus their 445 00:27:20,760 --> 00:27:25,240 Speaker 1: attention on operating the aircraft and also hear communications over 446 00:27:25,280 --> 00:27:29,120 Speaker 1: their headset without the interference of this incredibly loud noise. 447 00:27:29,320 --> 00:27:31,600 Speaker 1: And around the same time, the US Air Force was 448 00:27:31,640 --> 00:27:35,040 Speaker 1: researching ways to protect hearing while still allowing for communication, 449 00:27:35,280 --> 00:27:39,120 Speaker 1: and one of the projects involved active noise reduction. I'll 450 00:27:39,119 --> 00:27:42,280 Speaker 1: talk more about that in just a moment, but first 451 00:27:42,359 --> 00:27:55,080 Speaker 1: let's take another quick break. Okay. Before the break, I 452 00:27:55,160 --> 00:27:58,600 Speaker 1: mentioned that the US Air Force was looking for ways 453 00:27:58,640 --> 00:28:04,159 Speaker 1: to reduce noise in cockpits, and ultimately the Air Force 454 00:28:04,440 --> 00:28:09,800 Speaker 1: would pursue both passive and active measures to help protect hearing. 455 00:28:09,960 --> 00:28:13,720 Speaker 1: So again, passive measures are things like ear plugs or 456 00:28:14,240 --> 00:28:18,760 Speaker 1: insulated ear muffs that end up sealing the ear away 457 00:28:18,880 --> 00:28:22,919 Speaker 1: from noise so it's not canceling. So much as just blocking. 458 00:28:23,400 --> 00:28:26,280 Speaker 1: They also looked at active noise reduction and began to 459 00:28:26,359 --> 00:28:30,240 Speaker 1: develop their own version, largely based off the same work 460 00:28:30,280 --> 00:28:33,560 Speaker 1: that Fogel was doing. Now, ultimately the Air Force produced 461 00:28:33,680 --> 00:28:36,480 Speaker 1: some ear muffs that could reduce noise in the fifty 462 00:28:36,520 --> 00:28:41,160 Speaker 1: to five hundred hertz band of frequencies, so lower pitched frequencies, 463 00:28:41,560 --> 00:28:45,240 Speaker 1: and had an attenuation of twenty decibels. Now, again I 464 00:28:45,280 --> 00:28:49,240 Speaker 1: mentioned earlier what attenuation is that sound waves decrease in 465 00:28:49,240 --> 00:28:52,320 Speaker 1: intensity as they travel, and the further they go, the 466 00:28:52,320 --> 00:28:55,880 Speaker 1: more their intensity decreases, until they are no longer audible 467 00:28:56,000 --> 00:28:59,480 Speaker 1: to the typical human being. That reduction in sound amplitude 468 00:28:59,520 --> 00:29:03,240 Speaker 1: again is called attenuation. But then what's a decibel. So 469 00:29:03,680 --> 00:29:06,400 Speaker 1: decibel is a unit of measurement, but it's one in 470 00:29:06,440 --> 00:29:10,920 Speaker 1: which you're describing the relative strength of two signals, and 471 00:29:11,200 --> 00:29:16,320 Speaker 1: it's also a logarithmic metric as well. So this gets technical. 472 00:29:16,360 --> 00:29:18,920 Speaker 1: It's the logarithmic thing trips a lot of people up. 473 00:29:18,960 --> 00:29:21,560 Speaker 1: If you have two sounds and the second sound is 474 00:29:21,640 --> 00:29:25,160 Speaker 1: twice as loud as your reference sound, you would say 475 00:29:25,160 --> 00:29:27,280 Speaker 1: that the second sound is a little more than three 476 00:29:27,400 --> 00:29:31,080 Speaker 1: decibels louder than the first. It gets tricky stuff. Now, 477 00:29:31,160 --> 00:29:37,240 Speaker 1: generally speaking, zero decibels refers to the least perceptible sound, 478 00:29:37,480 --> 00:29:39,400 Speaker 1: like you can hear it, but if it were any 479 00:29:39,440 --> 00:29:43,120 Speaker 1: more quiet, you wouldn't. A ten decibel sound would be 480 00:29:43,160 --> 00:29:47,880 Speaker 1: approximately ten times louder than that reference sound, but a 481 00:29:48,120 --> 00:29:53,440 Speaker 1: twenty decibel sound would be one hundred times louder than 482 00:29:53,480 --> 00:29:57,680 Speaker 1: the reference sound. So human conversation is generally considered to 483 00:29:57,720 --> 00:30:00,680 Speaker 1: be around sixty decibels, unless you're talking to me, in 484 00:30:00,720 --> 00:30:03,760 Speaker 1: which case it'll be much louder because I am obnoxious. 485 00:30:04,200 --> 00:30:07,560 Speaker 1: A rock concert is regularly in the one hundred twenty 486 00:30:07,600 --> 00:30:10,440 Speaker 1: decibel range or even louder. That's also when you're getting 487 00:30:10,480 --> 00:30:13,920 Speaker 1: into the range of where loudness can cause hearing damage, 488 00:30:14,040 --> 00:30:17,160 Speaker 1: so where ear plugs when you go to your concerts, folks. 489 00:30:17,320 --> 00:30:20,760 Speaker 1: And also a minus twenty decibel attenuation could be the 490 00:30:20,760 --> 00:30:25,840 Speaker 1: difference between hearing loss and keeping safe from hearing loss. 491 00:30:26,280 --> 00:30:29,200 Speaker 1: So while all this work was going on, noise cancelation 492 00:30:29,320 --> 00:30:34,760 Speaker 1: technology remained largely in research facilities in various air vehicle 493 00:30:35,000 --> 00:30:39,880 Speaker 1: cockpits and military applications. In the late nineteen seventies that 494 00:30:39,920 --> 00:30:44,200 Speaker 1: would start to change, Doctor Amar Bows of the Bows 495 00:30:44,280 --> 00:30:49,080 Speaker 1: corporation decided to work on developing a consumer grade noise 496 00:30:49,240 --> 00:30:52,520 Speaker 1: reduction or cancelation headphone. He had apparently taken one too 497 00:30:52,520 --> 00:30:58,320 Speaker 1: many noisy airplane trips, so the industry had really taken 498 00:30:58,360 --> 00:31:04,280 Speaker 1: some steps to increase passenger comfort. But in the old days, 499 00:31:04,320 --> 00:31:09,240 Speaker 1: my drugies, the headphones and passenger planes worked via pneumatic tubes, 500 00:31:09,520 --> 00:31:12,440 Speaker 1: kind of like a stethoscope. So you would wear a 501 00:31:12,600 --> 00:31:16,560 Speaker 1: pair of hollow, flexible tubes that ended in little ear pieces, 502 00:31:16,760 --> 00:31:20,000 Speaker 1: and these would carry sound from a small speaker hidden 503 00:31:20,200 --> 00:31:23,200 Speaker 1: inside the armrest and would carry the sound from the 504 00:31:23,240 --> 00:31:26,840 Speaker 1: speaker up to your ears through these tubes. So if 505 00:31:26,840 --> 00:31:29,080 Speaker 1: you actually put your head very close to the armrest, 506 00:31:29,120 --> 00:31:31,160 Speaker 1: you could listen out of the lead a beaty speaker 507 00:31:31,200 --> 00:31:34,560 Speaker 1: in there. But all this changed with the introduction of 508 00:31:34,600 --> 00:31:40,400 Speaker 1: the Sony Walkman, which introduced inexpensive, mass produced electronic headsets. 509 00:31:40,840 --> 00:31:43,960 Speaker 1: Before those were just not a thing. You just didn't 510 00:31:44,040 --> 00:31:47,880 Speaker 1: have the cheap headsets really, But with the Sony Walkman, 511 00:31:47,960 --> 00:31:50,280 Speaker 1: that would change. You can actually listen to a recent 512 00:31:50,320 --> 00:31:52,800 Speaker 1: tech Stuff episode about the Sony Walkman to learn more 513 00:31:52,840 --> 00:31:56,320 Speaker 1: about that tech Bose would produce headphones that would have 514 00:31:56,480 --> 00:32:00,920 Speaker 1: a microphone set in each ear muff actually on the 515 00:32:00,960 --> 00:32:04,040 Speaker 1: outside of each ear muff, so the microphones led to 516 00:32:04,520 --> 00:32:08,920 Speaker 1: circuitry that could detect the incoming frequencies and amplitudes and 517 00:32:09,000 --> 00:32:11,760 Speaker 1: direct speakers in the ear muffs to produce an anti 518 00:32:11,800 --> 00:32:15,720 Speaker 1: phase signal. This all happened fast enough so that the 519 00:32:15,760 --> 00:32:20,080 Speaker 1: external sound waves and the internally generated anti phase signals 520 00:32:20,200 --> 00:32:23,680 Speaker 1: would both hit the wearer's ears at the same time, 521 00:32:24,040 --> 00:32:27,160 Speaker 1: thus canceling each other out. So you think about that 522 00:32:27,280 --> 00:32:30,120 Speaker 1: sound is coming at you. Before the sound can get 523 00:32:30,160 --> 00:32:32,960 Speaker 1: to your ear, it hits the outside of your headphones. 524 00:32:33,240 --> 00:32:36,440 Speaker 1: There a microphone picks up that sound, and through this 525 00:32:36,640 --> 00:32:40,760 Speaker 1: processing is able to figure out how to produce the 526 00:32:41,120 --> 00:32:45,440 Speaker 1: equal but opposite sound wave, and then both that and 527 00:32:45,520 --> 00:32:49,920 Speaker 1: the original sound from outside of the headphones combine and 528 00:32:50,000 --> 00:32:52,960 Speaker 1: you get silence or you get no noise. I guess 529 00:32:53,000 --> 00:32:55,479 Speaker 1: it depends on how you think about it. Now, this 530 00:32:55,560 --> 00:32:59,360 Speaker 1: all kind of sounds simple at least in concept, but 531 00:33:00,040 --> 00:33:03,760 Speaker 1: leaving it making it a reality was far from simple. 532 00:33:04,120 --> 00:33:07,000 Speaker 1: Bose and his team would spend a decade and a 533 00:33:07,120 --> 00:33:11,320 Speaker 1: half and more than fifty million dollars trying to figure 534 00:33:11,320 --> 00:33:14,880 Speaker 1: out how to make this technology effective enough and reliable 535 00:33:15,000 --> 00:33:18,120 Speaker 1: enough for the general consumer, how to have it where 536 00:33:18,640 --> 00:33:21,280 Speaker 1: you know you can actually draw power from something to 537 00:33:21,320 --> 00:33:24,680 Speaker 1: do this, because obviously that active part of active noise 538 00:33:24,720 --> 00:33:29,040 Speaker 1: canceling requires power to work. It's not like a microphone 539 00:33:29,080 --> 00:33:31,880 Speaker 1: and speaker is just going to work without any electricity. 540 00:33:32,280 --> 00:33:34,840 Speaker 1: So part of this was figuring out a way of 541 00:33:35,440 --> 00:33:40,280 Speaker 1: powering these headphones, preferably without requiring a wired connection. Like 542 00:33:40,360 --> 00:33:42,680 Speaker 1: a wired connection might be needed for you to be 543 00:33:42,720 --> 00:33:46,000 Speaker 1: able to play audio through the headset, whether that audio 544 00:33:46,080 --> 00:33:50,320 Speaker 1: is coming from a communications device or the entertainment system 545 00:33:50,360 --> 00:33:52,760 Speaker 1: of an airplane, but you don't want to have to 546 00:33:52,840 --> 00:33:56,440 Speaker 1: draw power as well. So the goal was to create 547 00:33:56,640 --> 00:34:01,680 Speaker 1: battery powered headphones, and it would take a long time 548 00:34:01,760 --> 00:34:04,960 Speaker 1: for that to become a consumer product. The earliest mention 549 00:34:05,080 --> 00:34:09,000 Speaker 1: I can find of a commercially available noise reduction set 550 00:34:09,040 --> 00:34:13,000 Speaker 1: of headphones was in nineteen eighty nine, when Bose released 551 00:34:13,000 --> 00:34:16,840 Speaker 1: the Series one Aviation headset, But even then this was 552 00:34:16,880 --> 00:34:21,200 Speaker 1: a product intended for the aviation industry, as the name suggests, 553 00:34:21,360 --> 00:34:24,160 Speaker 1: and it was good for reducing noise, but not eliminating it. 554 00:34:24,160 --> 00:34:26,959 Speaker 1: It would take another decade for the technology to start 555 00:34:26,960 --> 00:34:31,959 Speaker 1: appearing in mainstream consumer gear. In nineteen ninety nine, after 556 00:34:32,040 --> 00:34:35,520 Speaker 1: Bose had been producing active noise reduction and active noise 557 00:34:35,600 --> 00:34:39,040 Speaker 1: canceling headphones for the aviation industry as well as the military, 558 00:34:39,360 --> 00:34:42,960 Speaker 1: the company introduced a consumer model specifically for the Hoidy 559 00:34:43,000 --> 00:34:46,680 Speaker 1: toidies who were traveling first class on American airlines. The 560 00:34:46,719 --> 00:34:49,680 Speaker 1: movers and shakers appeared to really like the effect, and 561 00:34:49,760 --> 00:34:54,000 Speaker 1: Bose decided to introduce a consumer available version of the 562 00:34:54,040 --> 00:34:58,120 Speaker 1: technology in two thousand. It was called the Quiet Comfort Series. 563 00:34:58,719 --> 00:35:02,760 Speaker 1: Other companies started doing the same. Sennheiser actually created active 564 00:35:02,800 --> 00:35:05,960 Speaker 1: noise canceling headphones for pilots at Luftonza in the mid 565 00:35:06,080 --> 00:35:09,520 Speaker 1: nineteen eighties, so they were producing their headsets the same 566 00:35:09,600 --> 00:35:12,719 Speaker 1: time BOS was, in fact, at least for the If 567 00:35:12,800 --> 00:35:16,960 Speaker 1: you're looking at the first series that BOS released, Sennheiser 568 00:35:17,000 --> 00:35:20,000 Speaker 1: came out with THEIRS a couple of years earlier, but 569 00:35:20,080 --> 00:35:23,319 Speaker 1: Bose had had prototypes for several years at that point too, 570 00:35:23,400 --> 00:35:27,080 Speaker 1: so it's kind of complicated. These days, lots of companies 571 00:35:27,239 --> 00:35:31,680 Speaker 1: have noise canceling or noise reduction headphones. Apple released the 572 00:35:31,760 --> 00:35:35,799 Speaker 1: Airpod's Max headset back in December twenty twenty, with a 573 00:35:35,960 --> 00:35:41,200 Speaker 1: Bluetooth headset this year, so nos released its wireless noise 574 00:35:41,200 --> 00:35:45,080 Speaker 1: canceling headphones, the so nos ace so the technology, even 575 00:35:45,080 --> 00:35:47,439 Speaker 1: though it has its roots in the nineteen thirties, it's 576 00:35:47,480 --> 00:35:51,239 Speaker 1: only been available for customers like you and me for 577 00:35:51,320 --> 00:35:54,920 Speaker 1: the last couple of decades, and for those of us 578 00:35:54,960 --> 00:35:58,760 Speaker 1: who are perhaps not in the tax bracket that travels 579 00:35:58,760 --> 00:36:02,360 Speaker 1: first class in a regular base. It's a relatively recent development. 580 00:36:02,800 --> 00:36:05,480 Speaker 1: They're pretty neat, and if you really like to focus 581 00:36:05,560 --> 00:36:09,920 Speaker 1: on music or other audio, they are essential. I certainly 582 00:36:09,960 --> 00:36:13,160 Speaker 1: think of them as being a necessary technology to bring 583 00:36:13,239 --> 00:36:16,319 Speaker 1: with you when you're on airplane trips. It is a 584 00:36:16,360 --> 00:36:20,239 Speaker 1: sanity saver, just reducing like the hum of the aircraft 585 00:36:20,280 --> 00:36:23,240 Speaker 1: and all that kind of stuff. It doesn't eliminate all noise, 586 00:36:23,680 --> 00:36:28,160 Speaker 1: like you could typically hear certain things outside of bands 587 00:36:28,160 --> 00:36:30,480 Speaker 1: of frequencies. A lot of these are designs that you 588 00:36:30,480 --> 00:36:32,840 Speaker 1: can still hear if someone talks to you. And of 589 00:36:32,880 --> 00:36:34,880 Speaker 1: course there are also a lot of headsets that have 590 00:36:35,160 --> 00:36:39,880 Speaker 1: like a pass through feature where instead of blocking noise, 591 00:36:39,960 --> 00:36:43,560 Speaker 1: it allows external noise to reach your ears more clearly, 592 00:36:43,920 --> 00:36:46,920 Speaker 1: so that you can stay aware of your environment. That way, 593 00:36:46,960 --> 00:36:49,440 Speaker 1: if you're in someplace like let's say you're walking along 594 00:36:49,480 --> 00:36:52,080 Speaker 1: a warehouse floor or something. You're not going to be 595 00:36:52,120 --> 00:36:55,279 Speaker 1: taken by surprise by like a forklift or something like 596 00:36:55,320 --> 00:36:59,880 Speaker 1: that just suddenly appearing behind you. So there are variations 597 00:37:00,080 --> 00:37:03,160 Speaker 1: this technology as well, but that's how it works. I 598 00:37:03,200 --> 00:37:06,160 Speaker 1: hope you found that interesting, and I hope you are 599 00:37:06,239 --> 00:37:10,360 Speaker 1: all doing well, and I'll talk to you again really soon. 600 00:37:16,719 --> 00:37:21,359 Speaker 1: Tech Stuff is an iHeartRadio production. For more podcasts from iHeartRadio, 601 00:37:21,719 --> 00:37:25,440 Speaker 1: visit the iHeartRadio app, Apple Podcasts, or wherever you listen 602 00:37:25,440 --> 00:37:26,520 Speaker 1: to your favorite shows.