Speaker 1: Welcome to tech Stuff, a production from iHeartRadio. Hey there,
Speaker 1: and welcome to tech Stuff. I'm your host, Jonathan Strickland.
Speaker 1: I'm an executive producer with iHeart Podcasts and how the
Speaker 1: tech are you? So today I figured I would talk
Speaker 1: about noise canceling technologies specifically in headphones, although you can
Speaker 1: employ these technologies in other use cases. And it's largely
Speaker 1: because I'm actually wearing a pair of noise canceling headphones
Speaker 1: right now as I record this episode. I'll talk more
Speaker 1: about those headphones in a future episode. I'm actually just
Speaker 1: trying them out now to make sure that I like
Speaker 1: how they work and all of that. But for now,
Speaker 1: I just wanted to talk about the science and technology
Speaker 1: behind active noise canceling or active noise reduction headphones. An
Speaker 1: R and ANC are the acronyms or initialisms, I should say,
Speaker 1: not acronyms that are used for those technologies. Now, noise
Speaker 1: canceling is more than just muffling sound. You can have
Speaker 1: passive noise canceling, which really just means things like ear
Speaker 1: plugs or really well insulated ear muffs. So it's more
Speaker 1: than that. It's not just soundproofing your ears or something.
Speaker 1: It's using technology to actively cancel out the sound waves
Speaker 1: that are heading for your ear drums. But we won't
Speaker 1: get ahead of ourselves. First, let's talk about what sound is. So,
Speaker 1: when you get down to it, sound is vibration, and
Speaker 1: we can think of vibration as energy. So this energy
Speaker 1: needs a medium to travel through. Sound travels through matter,
Speaker 1: and it doesn't matter if the matter is solid, liquid,
Speaker 1: or gas. It can travel through it, but it definitely
Speaker 1: needs to have a medium in order to try. This
Speaker 1: is why out in space there is no sound. You know,
Speaker 1: in space, no one can hear you scream. Well, that's
Speaker 1: because in space you have these vast regions where there
Speaker 1: is so little matter out there that sound cannot pass
Speaker 1: through it. There's nothing for the sound to transfer energy to.
Speaker 1: So it's not just that it's a lack of air,
Speaker 1: it's that it's a lack of anything, or at least
Speaker 1: there's not enough significant amount of anything out there that
Speaker 1: would allow for the transfer of longitudinal waves. By the way,
Speaker 1: that's how sound travels. Sound travels in longitudinal waves. So
Speaker 1: broadly speaking, there are two types of waves. There's longitudinal
Speaker 1: and there's transverse. Transverse waves are what I think a
Speaker 1: lot of folks imagine when they think of waves, often
Speaker 1: it's how we plot waves on a chart. It's a
Speaker 1: very easy way of doing it. So one way you
Speaker 1: could actually see transverse waves in action is just with
Speaker 1: a length of rope, a nice long length of The
Speaker 1: longer the better, really, because it's easier to see. And
Speaker 1: if you had a long length of rope and you
Speaker 1: picked up just one end of it, it's laid out
Speaker 1: straight in front of you. Then you started to move
Speaker 1: the end of the rope from side to side, left
Speaker 1: to right back again, over and over again. You would
Speaker 1: see waves traveled down the length of the rope. But
Speaker 1: this means that the wave is traveling at like a
Speaker 1: ninety degree angle from the disturbance of the medium, because
Speaker 1: again you're moving the rope left and right. You're not
Speaker 1: pushing on the rope. You're moving the rope left and right,
Speaker 1: but the waves are traveling down the rope. By the way,
Speaker 1: the same thing would happen if you were moving the
Speaker 1: rope up and down right. If you moved them up
Speaker 1: and down, you would still see the disturbance happening up
Speaker 1: and down, but the direction of the waves travel would
Speaker 1: be forward down the length of rope. Now, a longitudinal
Speaker 1: wave is different. The wave travels in the same direction
Speaker 1: as the disturbance rather at a ninety degree angle from it.
Speaker 1: So in this case, if the rope behaved like a
Speaker 1: longitudinal wave, if you pushed on the end of the rope,
Speaker 1: you would see the disturbance and wave traveled down the length.
Speaker 1: But that doesn't happen with rope. However, it does happen
Speaker 1: with one of the most important tools in any serious
Speaker 1: scientist's tool box. I'm talking about a slinky for fun.
Speaker 1: It's a wonderful toy. So if you take a slinky
Speaker 1: and you stretch it out a little bit between two people,
Speaker 1: and then you ask one of those two people to
Speaker 1: push the slinky forward really quickly, you would observe that
Speaker 1: you would see a wave travel forward through the slinky
Speaker 1: in the direction of the push. Areas of the slinky
Speaker 1: would compress as this wave travels down, and in fact,
Speaker 1: in the longitudinal wave business, we would call that compression.
Speaker 1: Areas where the slinky links would be further apart as
Speaker 1: the wave would travel through the medium, we would call
Speaker 1: that rare faction. So you have rare faction and compression.
Speaker 1: Now for the purposes of illustration, we often will draw
Speaker 1: sound waves almost as if they were transverse waves. It's
Speaker 1: just easier to see the parts of a wave that way.
Speaker 1: So if we did that, if we had like your
Speaker 1: your regular little graph, and we had a sound wave
Speaker 1: drawn on there, similar to a transverse wave, you would
Speaker 1: have peaks and you would have valleys, right, because that's
Speaker 1: the way we envision these, these transverse waves. And it's
Speaker 1: pretty simple to see a single wavelength, you know. You
Speaker 1: just go from one peak to the following peak. That's
Speaker 1: one wavelength. And it's not too hard to understand stuff
Speaker 1: like amplitude and frequency. So amplitude describes how high those
Speaker 1: peaks are from the center line, or how low the
Speaker 1: troughs are, if you will, And we would say that
Speaker 1: this correlates to volume with sound waves. Frequency would be
Speaker 1: how how many wavelengths are passing a given point in
Speaker 1: a fixed amount of time. This correlates to a sound's pitch.
Speaker 1: The higher frequencies are higher pitches. But it would be
Speaker 1: more accurate to illustrate this as a longitudinal wave, because
Speaker 1: that's how sound travels. Wavelengths and longitudinal waves refer to
Speaker 1: the distance between say one point of compression to the
Speaker 1: next point of compression, or we could actually measure it
Speaker 1: from one point of rarefaction to the next point of
Speaker 1: rare affection. That would still be a wavelength. Frequency is
Speaker 1: fairly simple. It's the number of compressions or rare factions,
Speaker 1: depending on which one you're starting with. In other words,
Speaker 1: the number of wavelengths that pass a given point in
Speaker 1: a fixed amount of time. Amplitude is a little bit different.
Speaker 1: It's the distance between points of compression within the sound wave.
Speaker 1: If a sound wave has many points of compression that
Speaker 1: are close to one another, it's high amplitude a loud sound.
Speaker 1: If there's a wave that has fewer points of compression
Speaker 1: and that maybe they're a little further apart from each other,
Speaker 1: it's low amplitude. Its lower volume. So with sound, we
Speaker 1: have something that's causing a vibration, and it could be anything, right.
Speaker 1: It could be a tree following in the forest as
Speaker 1: long as someone's there to hear it. It might be
Speaker 1: a flower pot falling on the pavement. It could be
Speaker 1: a fiddler drawing a bow across violin strings. It might
Speaker 1: be a mine being tortured. It could be anything. The
Speaker 1: sound travels out in all directions from the source, and
Speaker 1: it travels through whatever medium it's in. The sound most
Speaker 1: of us encounter most of the time is traveling through air,
Speaker 1: but this also works underwater or even through solid matter. Now,
Speaker 1: if these vibrations fall within the range of human hearing,
Speaker 1: then we might very well hear them, as long as
Speaker 1: we're close enough for those vibrations to get to us
Speaker 1: before they peter out. That's called attenuation. By the way,
Speaker 1: the sound attenuates as it travels from its source, That
Speaker 1: means it gets weaker as it travels out further from
Speaker 1: the source of sound, which makes sense right. Otherwise we
Speaker 1: wouldn't be able to hear anything. Everything would just be
Speaker 1: equally loud to us all the time, or it would
Speaker 1: be of the same amplitude as the original sound was
Speaker 1: and we'd all be deafened by it. So yeah, sound
Speaker 1: diminishes in strength as it travels. Now, the range of
Speaker 1: typical human hearing falls between twenty hurts or twenty vibrations
Speaker 1: per second up to twenty killer hurts or twenty thousand
Speaker 1: vibrations per second. Now, as I mentioned earlier, the lower
Speaker 1: frequencies have lower pitches, So a twenty hurtz sound would
Speaker 1: be a very deep bass sound. In fact, some of
Speaker 1: those you might feel more than you hear them, depending
Speaker 1: upon your hearing, and as we get older, we typically
Speaker 1: lose some of the ability to hear the higher pitches.
Speaker 1: I think the last hearing test I did said my
Speaker 1: hearing kind of tops out around fifteen or sixteen killer hurtz,
Speaker 1: So thatre's a lot of space between the upper limits
Speaker 1: of my hearing and the typical range for human hearing.
Speaker 1: Part of that is just because I'm old, and part
Speaker 1: of that is also because I saw a lot of
Speaker 1: rock concerts or rock shows. I can't call them concerts
Speaker 1: rock shows when I was in college, thanks to Dick
Speaker 1: Dale and the Dell Tones and the Hate Bombs and
Speaker 1: the Woggles and all the other bands I saw that
Speaker 1: ruined my hearing. It's really my fault. I should have
Speaker 1: worn earplugs anyway. Younger people can still hear those higher
Speaker 1: frequencies typically. I mean we always have to say typically,
Speaker 1: because there are obviously exceptions. But you may have heard
Speaker 1: that some businesses have even installed speakers that would play very,
Speaker 1: very high pitched sounds in order to discourage youngsters from
Speaker 1: loitering at that place of business, Like convenience stores and stuff,
Speaker 1: so the adults could shop in peace, and all those young,
Speaker 1: unruly hooligans would be chased out by unpleas a high
Speaker 1: pitched noise. I did a cursory search on this and
Speaker 1: found devices that are called mosquito alarms. These alarms push
Speaker 1: out sound at high amplitude. But if you're like me
Speaker 1: and you've lost hearing in those frequency ranges, well it
Speaker 1: don't bug you none. You don't hear it even though
Speaker 1: it's being played at high volume. But meanwhile, all the
Speaker 1: little tykes grab their ears and run off, and it
Speaker 1: leaves me to buy my slim gems in peace. I'm
Speaker 1: mostly kidding about that. I'm not that grouchy. I'm not
Speaker 1: really a fan of making spaces inherently unwelcome to slices
Speaker 1: of demographics. Also, I don't eat slim gems. Apologies to
Speaker 1: Randy Savage. Anyway. Let's talk about the perception of sound.
Speaker 1: So when sound waves enter our ears, the wave travels
Speaker 1: to the tympanic membrane, which is also known as the
Speaker 1: ear drum. So the sound wave transfers vibrations to this membrane,
Speaker 1: and it's actually doing that through very small changes in
Speaker 1: air pressure in our ear canals, so these small changes
Speaker 1: in air pressure are essentially pushing and pulling against that membrane. Now,
Speaker 1: the membrane in turn transfers those vibrations to three very
Speaker 1: tiny delicate bones in our middle ears. Those are the hammer,
Speaker 1: the anvil, and the stirrup, and they're called that because
Speaker 1: that's kind of what they look like. And these tiny
Speaker 1: bones kind of act like an amplifier, and they send
Speaker 1: the vibrations further along into the inner ear, where a
Speaker 1: snail shaped structure called the cochlea sits. Now, the cochlea
Speaker 1: contains fluid within it, and the vibrations to the cochlea
Speaker 1: make this fluid ripple. This in turn creates a wave
Speaker 1: on the membrane that lines the cochlea. And there are
Speaker 1: these little hair like protrusions inside the cochlea. They're called stereocilia.
Speaker 1: They vibrate from all this rippling, and they transfer those vibrations,
Speaker 1: this physical vibration into electrical impulses. Those impulse is then
Speaker 1: travel to our brains and the brain interprets the these
Speaker 1: a sound. So ultimately the sounds we encounter are in
Speaker 1: a sense all in our heads. Thus the question if
Speaker 1: a tree falls in the forest and no one is
Speaker 1: there to hear it, does it make a sound? You
Speaker 1: could argue, really, sound only exists within the mind, and
Speaker 1: if there is no mind to perceive it, there is
Speaker 1: no sound. Our brains create the perception of that sound.
Speaker 1: So this raises a question, is what we hear actually
Speaker 1: what is happening out in reality? If somehow we were
Speaker 1: able to step outside of the experience of being human
Speaker 1: and to perceive things as they truly are, would sounds
Speaker 1: appear to be anything like what we perceive. Now that's
Speaker 1: a question for philosophers, but you know, it sure would
Speaker 1: be interesting if we found out that every single person's
Speaker 1: experiences sound differently like. It's just that collectively we all
Speaker 1: agree that the thing causing the sound is awesome, like
Speaker 1: maybe a new they might be Giant's song, or that
Speaker 1: it's awful like a new kid rock song. Just having
Speaker 1: fun here, But no, Seriously, because it's impossible for us
Speaker 1: to step into the experience of someone else, we can't
Speaker 1: really be sure that the way we experience sound is
Speaker 1: the same as what other people experience kind of the
Speaker 1: same way. That there's no way for me to know
Speaker 1: if the shade of blue I see when I look
Speaker 1: in the sky is the same experience you have when
Speaker 1: you do the same thing. Now, I know I'm getting
Speaker 1: a little bit whibbly wobbly here, But acoustics, the science
Speaker 1: of sound involves a lot of psychology. If you listen
Speaker 1: to my episodes about the MP three format, you know
Speaker 1: that one way MP three's can serve filespace is the
Speaker 1: compression algorithm ditches any sounds deemed to be beyond human perception.
Speaker 1: Like if a very quiet sound follows a very loud sound,
Speaker 1: typically we can't hear the quiet one. The loud one
Speaker 1: as almost kind of deadened ust to being able to
Speaker 1: hear the quiet one. And I'm talking about like these
Speaker 1: sounds are like back to back one raft or the other.
Speaker 1: So the compression algorithm would say, oh, well, no one's
Speaker 1: going to be able to hear the second sound in
Speaker 1: the first place, so why would be encode it? Just
Speaker 1: leave it out, and thus it conserves filespace. Of course,
Speaker 1: if you start to ditch stuff humans actually can perceive,
Speaker 1: you begin to affect the quality of sound, and then
Speaker 1: you have problems with the decline and quality. All right,
Speaker 1: I've got tons more to say, and Obviously, we haven't
Speaker 1: even gotten to active noise cancelation yet, So let's take
Speaker 1: a quick break and we'll be right back. Okay, we're back,
Speaker 1: and we're going back to sound waves. So you might
Speaker 1: recall that the speed of light is constant, which is
Speaker 1: kind of true, but not all the truth. The speed
Speaker 1: of light is constant given the medium through which it travels.
Speaker 1: When light from the Sun reaches Earth, it actually slows
Speaker 1: down a little bit as that light hits our atmosphere.
Speaker 1: And by a little bit, I mean a very small amount,
Speaker 1: small enough to be deemed insignificant based upon like the
Speaker 1: speed it travels through a vacuum versus the speed it
Speaker 1: travels through air, insignificant for most calculations. I mean, it
Speaker 1: does happen, but it's a very tiny change. The ratio
Speaker 1: of difference between the faster and slower rates is called
Speaker 1: the refractive index. I'm getting a little off topic, although
Speaker 1: the same thing kind of happens with sound too, But sound,
Speaker 1: like light, will travel at different speeds depending upon the
Speaker 1: medium through which it travels. Moreover, the temperature of the
Speaker 1: medium will affect how fast sound is able to travel
Speaker 1: through it. Sound travels faster through hot air than it
Speaker 1: does through cold air. Now, when you think about it,
Speaker 1: that makes sense. Sound is vibration. Hot air has molecules
Speaker 1: and atom They have more energy in them, so they're
Speaker 1: more inclined to vibrate. They're already moving around. They'll carry
Speaker 1: movement more easily than cold air does because cold air
Speaker 1: has less energy in it, so the vibrations come less readily.
Speaker 1: This gets reflected in the speed of sound. Sound traveling
Speaker 1: on a day that's around sixty degrees fahrenheit, we'll move
Speaker 1: it about two and twenty kilometers per hour. But let's
Speaker 1: say it's a really chilly night, like negative sixty seven
Speaker 1: degrees fahrenheit. Then you're talking about sound travel I get
Speaker 1: around one than fifty six kilometers per hour. Though, you know,
Speaker 1: if you're out in weather that's that cold, the speed
Speaker 1: of sound probably isn't is you know, not top of
Speaker 1: mind to you. You're probably thinking, how do I get
Speaker 1: inside before I freeze to death. Now let's get back
Speaker 1: to sound waves in order to understand how noise cancelation
Speaker 1: actually works. All right, So I mentioned earlier. Sound waves
Speaker 1: have wavelengths, and we describe the frequency of sound by
Speaker 1: the number of wavelengths that pass a fixed point in
Speaker 1: space within a given amount of time. So if we're
Speaker 1: using hurts as our measurement, the amount of time is
Speaker 1: one second. So let's say that you are able to
Speaker 1: see sound waves and you're able to count really fast,
Speaker 1: like time to you doesn't pass the same way it
Speaker 1: does to everybody else, and you use a stop watch
Speaker 1: so that you can click down a single second. Meanwhile,
Speaker 1: you're counting all the sound waves that go past you. Well,
Speaker 1: if you did that, the number you would come up
Speaker 1: to that would be the sound's frequency. In hurts, the
Speaker 1: amount of time it takes just one wavelength to pass
Speaker 1: a fixed point is called a period. So for a
Speaker 1: twenty Hurtz sound, a period is just one twentieth of
Speaker 1: a second. That's how long it would take a single
Speaker 1: wavelength to complete one cycle. So if we were to
Speaker 1: further divide that period into even smaller fractions, we could
Speaker 1: call those phases. To get into phases in detail would
Speaker 1: really require visual aid, because otherwise I would just start
Speaker 1: spouting off formula to you and it would all get
Speaker 1: very confusing for me. Really. I mean, you might be fine,
Speaker 1: but I would inevitably say something wrong. So I'm not
Speaker 1: even gonna bother doing it because I'll just mess it up.
Speaker 1: But if you have two or more waves, and let's
Speaker 1: say all of these waves, these are sound waves, they
Speaker 1: are longitudinal. So let's say all these waves are aligned
Speaker 1: in that they have the same areas of compression and rarefaction.
Speaker 1: As they travel past a fixed point, those sound waves
Speaker 1: would be said to be in phase with one another.
Speaker 1: They're all kind of traveling at the same speed in
Speaker 1: the same direction. But let's say you have sound wave
Speaker 1: A and it travels with its various compression and rare
Speaker 1: faction zones, and then you've got sound wave B. But
Speaker 1: soundwave b's compression zones are matching with a's rarefaction zones,
Speaker 1: and b's rarefaction zones are matching with a's compression zones.
Speaker 1: So they're opposite. They're like the opposite sides of a
Speaker 1: puzzle fitting in together. And let's say they match each
Speaker 1: other in amplitude, so they're both the same volume. Well
Speaker 1: what happens at that point, Well, what happens is they
Speaker 1: cancel each other out. It's called destructive interference. Essentially, it
Speaker 1: all comes down to math. If we were to assign
Speaker 1: values to these waves, then maybe we say wave A
Speaker 1: is at value two at a given point, while wave
Speaker 1: B is at negative two. So then we add these
Speaker 1: two together two plus negative two equals zero. Now that
Speaker 1: is an oversimplification of what's going on here, but it's
Speaker 1: basically the concept behind noise cancelation. Now, if we think
Speaker 1: of transverse waves, which I think are easier to imagine,
Speaker 1: this would be like having two waves where the peaks
Speaker 1: of wave A are matched up with the values of
Speaker 1: wave B and vice versa, and that the height the
Speaker 1: amplitude of those peaks and valleys is exactly the same,
Speaker 1: and what we get ultimately is cancelation. The two waves
Speaker 1: sound waves in this case, eliminate each other and we
Speaker 1: hear nothing as a result. Or if you prefer those
Speaker 1: differences in air pressure that happens in our ear canals
Speaker 1: that ultimately we end up perceiving as sound. Those differences
Speaker 1: never happen because while one sound wave is pushing one way,
Speaker 1: the other sound wave is pushing the other way with
Speaker 1: equal force, and the air particles don't do anything, they
Speaker 1: don't go anywhere, So therefore we hear nothing. But getting
Speaker 1: to that point where we could actually create technology that
Speaker 1: could detect incoming sound and then produce out of phase
Speaker 1: equivalence for the purposes of eliminating that sound. That would
Speaker 1: take a lot of time, the better part of a
Speaker 1: century actually now. One person who suggested an approach to
Speaker 1: do this was a doctor of philosophy and medicine in
Speaker 1: Germany back in the nineteen thirties. His name was Paul Lug,
Speaker 1: and he applied for a patent that he titled process
Speaker 1: of Silencing Sound Oscillations. Now, the patent application begins by
Speaker 1: explaining that up to that point, the only way to
Speaker 1: cancel displeasing oscillations was to build in mechanical solutions at
Speaker 1: the source of the noise itself. His invention would allow
Speaker 1: for the installation of noise canceling technology that was independent
Speaker 1: of the source of the noise. So, instead of trying
Speaker 1: to figure out a way to mechanically alter a process
Speaker 1: so that it produced less noise, you could use Lug's
Speaker 1: invention to eliminate noise no matter where it came from,
Speaker 1: because this device would be able to take in incoming
Speaker 1: noise and produce the anti phase version of it. He
Speaker 1: described the basic components of noise cancelation, and in his
Speaker 1: description he mentioned microphones or receivers which would detect incoming
Speaker 1: sound waves and a quote unquote reproducing apparatus. In other words,
Speaker 1: essentially a loud speaker of some sort that would produce
Speaker 1: sounds having an opposite phase to the incoming noise. The
Speaker 1: opposing phase sound waves would then cancel each other out.
Speaker 1: Lug also mentioned ways to eliminate only part of a
Speaker 1: noise or only specific types of noises. So he thought
Speaker 1: this would be handy if you needed to eliminate noises
Speaker 1: and loud environments while still allowing people to speak with
Speaker 1: one another. So how do you eliminate noise but you
Speaker 1: allow signal to get through? That was what he was
Speaker 1: talking about. He was also thinking about ways to eliminate
Speaker 1: unwanted noises in places like say a theater or a
Speaker 1: concert hall, where maybe you go to the concert hall
Speaker 1: and the music is fantastic, but there's some element, some
Speaker 1: acoustic element in that environment. This is producing something that
Speaker 1: was not wanted, that is detracting from the experience of
Speaker 1: hearing this concert. Luke said, well, we could create this
Speaker 1: technology that would detect this unwanted frequency, like we would
Speaker 1: tune it to that and then produce the anti phase
Speaker 1: version and then you could just enjoy the concert as
Speaker 1: it was intended, without any of these unpleasant secondary noises
Speaker 1: mixed in. Now, Luke's idea was pretty solid. Unfortunately, the
Speaker 1: technology was nowhere near where it needed to be in
Speaker 1: order to actually realize his idea was He did get
Speaker 1: his patent, he got that, granted, but he was getting
Speaker 1: a lot of resistance in the academic world of Germany
Speaker 1: because I think a lot of other people realized they
Speaker 1: just couldn't accomplish what he was suggesting. Not that what
Speaker 1: he was saying was impossible from a science perspective, but
Speaker 1: on a technical level they couldn't figure it out. And moreover,
Speaker 1: things in Germany were obviously getting rather tense in the
Speaker 1: nineteen thirties as the world continued to plunge toward total
Speaker 1: war in the region. Now I tried to find out
Speaker 1: more information about lug and I did discover a paper
Speaker 1: that was written in German that was all about him
Speaker 1: and his life both before and after his proposed invention. Now,
Speaker 1: my German is awful. I am not at all fluent,
Speaker 1: so I depended heavily, really entirely on Google Translate, and
Speaker 1: was only partially successful in translating the article because the
Speaker 1: translation just wasn't fantastic. However, from what I can figure out,
Speaker 1: Luke discovered that some engineers in England were attempting to
Speaker 1: build an invention that was really similar to the one
Speaker 1: he described in his pat and he suspected that someone
Speaker 1: somewhere along the way had leaked his invention and allow
Speaker 1: people in England to read about it and try and
Speaker 1: create the thing that he had proposed, So he wrote
Speaker 1: a letter to the German Patent Office demanding an explanation.
Speaker 1: This turned out to be a bad move because the
Speaker 1: Nazis were steadily gaining control of all of Germany's political
Speaker 1: systems and they were not super keen to be called
Speaker 1: into question, and they in turn decided to turn scrutiny
Speaker 1: onto Luke, and he was reprimanded for his insolence, and
Speaker 1: apparently he spent the next decade in fear of what
Speaker 1: might happen to him and his family. You know, those
Speaker 1: Nazis held a grudge. And he also couldn't get a
Speaker 1: job as a physicist. It appeared that he had been blacklisted,
Speaker 1: so instead he trained to be a doctor. Now, he
Speaker 1: survived well after the war, but from what he can tell,
Speaker 1: he never really got to work on noise cancelation again. Instead,
Speaker 1: we're going to have to leap on over to the
Speaker 1: nineteen fifties. An American scientist and engineer named Lawrence J.
Speaker 1: Fogel would become a key figure in no cancelation, to
Speaker 1: the point where many will refer to Fogel as the
Speaker 1: inventor of active noise cancelation. I'm not sure that's entirely fair,
Speaker 1: because you know, Lug certainly patented it back in the
Speaker 1: nineteen thirties, but he never got it to work, Like
Speaker 1: the technology wasn't there, So I guess you could argue
Speaker 1: that Fogel is the inventor in the sense that Fogel
Speaker 1: was able to create an actual working prototype of noise
Speaker 1: reduction headphones. He had done a great deal of scientific
Speaker 1: and practical engineering work in wave dynamics. This guy was
Speaker 1: like super smart and studied lots of different disciplines, and
Speaker 1: he knew a lot about wave interactions and wave interference.
Speaker 1: He had worked in not just sound waves, but like
Speaker 1: electromagnetic waves VHF and UHF waves, and he understood about
Speaker 1: waves and how they perform when they are in antiphase
Speaker 1: with one another, how that can result in destructive interference.
Speaker 1: He also knew there was a need for better ear
Speaker 1: protection for folks who were working in very noisy environments,
Speaker 1: specifically in the cockpits of aircraft like helicopters and airplanes,
Speaker 1: and he theorized that he could build a set of
Speaker 1: headphones that could diminish or even eliminate the noise of
Speaker 1: propeller driven aircraft so that the pilot could focus their
Speaker 1: attention on operating the aircraft and also hear communications over
Speaker 1: their headset without the interference of this incredibly loud noise.
Speaker 1: And around the same time, the US Air Force was
Speaker 1: researching ways to protect hearing while still allowing for communication,
Speaker 1: and one of the projects involved active noise reduction. I'll
Speaker 1: talk more about that in just a moment, but first
Speaker 1: let's take another quick break. Okay. Before the break, I
Speaker 1: mentioned that the US Air Force was looking for ways
Speaker 1: to reduce noise in cockpits, and ultimately the Air Force
Speaker 1: would pursue both passive and active measures to help protect hearing.
Speaker 1: So again, passive measures are things like ear plugs or
Speaker 1: insulated ear muffs that end up sealing the ear away
Speaker 1: from noise so it's not canceling. So much as just blocking.
Speaker 1: They also looked at active noise reduction and began to
Speaker 1: develop their own version, largely based off the same work
Speaker 1: that Fogel was doing. Now, ultimately the Air Force produced
Speaker 1: some ear muffs that could reduce noise in the fifty
Speaker 1: to five hundred hertz band of frequencies, so lower pitched frequencies,
Speaker 1: and had an attenuation of twenty decibels. Now, again I
Speaker 1: mentioned earlier what attenuation is that sound waves decrease in
Speaker 1: intensity as they travel, and the further they go, the
Speaker 1: more their intensity decreases, until they are no longer audible
Speaker 1: to the typical human being. That reduction in sound amplitude
Speaker 1: again is called attenuation. But then what's a decibel. So
Speaker 1: decibel is a unit of measurement, but it's one in
Speaker 1: which you're describing the relative strength of two signals, and
Speaker 1: it's also a logarithmic metric as well. So this gets technical.
Speaker 1: It's the logarithmic thing trips a lot of people up.
Speaker 1: If you have two sounds and the second sound is
Speaker 1: twice as loud as your reference sound, you would say
Speaker 1: that the second sound is a little more than three
Speaker 1: decibels louder than the first. It gets tricky stuff. Now,
Speaker 1: generally speaking, zero decibels refers to the least perceptible sound,
Speaker 1: like you can hear it, but if it were any
Speaker 1: more quiet, you wouldn't. A ten decibel sound would be
Speaker 1: approximately ten times louder than that reference sound, but a
Speaker 1: twenty decibel sound would be one hundred times louder than
Speaker 1: the reference sound. So human conversation is generally considered to
Speaker 1: be around sixty decibels, unless you're talking to me, in
Speaker 1: which case it'll be much louder because I am obnoxious.
Speaker 1: A rock concert is regularly in the one hundred twenty
Speaker 1: decibel range or even louder. That's also when you're getting
Speaker 1: into the range of where loudness can cause hearing damage,
Speaker 1: so where ear plugs when you go to your concerts, folks.
Speaker 1: And also a minus twenty decibel attenuation could be the
Speaker 1: difference between hearing loss and keeping safe from hearing loss.
Speaker 1: So while all this work was going on, noise cancelation
Speaker 1: technology remained largely in research facilities in various air vehicle
Speaker 1: cockpits and military applications. In the late nineteen seventies that
Speaker 1: would start to change, Doctor Amar Bows of the Bows
Speaker 1: corporation decided to work on developing a consumer grade noise
Speaker 1: reduction or cancelation headphone. He had apparently taken one too
Speaker 1: many noisy airplane trips, so the industry had really taken
Speaker 1: some steps to increase passenger comfort. But in the old days,
Speaker 1: my drugies, the headphones and passenger planes worked via pneumatic tubes,
Speaker 1: kind of like a stethoscope. So you would wear a
Speaker 1: pair of hollow, flexible tubes that ended in little ear pieces,
Speaker 1: and these would carry sound from a small speaker hidden
Speaker 1: inside the armrest and would carry the sound from the
Speaker 1: speaker up to your ears through these tubes. So if
Speaker 1: you actually put your head very close to the armrest,
Speaker 1: you could listen out of the lead a beaty speaker
Speaker 1: in there. But all this changed with the introduction of
Speaker 1: the Sony Walkman, which introduced inexpensive, mass produced electronic headsets.
Speaker 1: Before those were just not a thing. You just didn't
Speaker 1: have the cheap headsets really, But with the Sony Walkman,
Speaker 1: that would change. You can actually listen to a recent
Speaker 1: tech Stuff episode about the Sony Walkman to learn more
Speaker 1: about that tech Bose would produce headphones that would have
Speaker 1: a microphone set in each ear muff actually on the
Speaker 1: outside of each ear muff, so the microphones led to
Speaker 1: circuitry that could detect the incoming frequencies and amplitudes and
Speaker 1: direct speakers in the ear muffs to produce an anti
Speaker 1: phase signal. This all happened fast enough so that the
Speaker 1: external sound waves and the internally generated anti phase signals
Speaker 1: would both hit the wearer's ears at the same time,
Speaker 1: thus canceling each other out. So you think about that
Speaker 1: sound is coming at you. Before the sound can get
Speaker 1: to your ear, it hits the outside of your headphones.
Speaker 1: There a microphone picks up that sound, and through this
Speaker 1: processing is able to figure out how to produce the
Speaker 1: equal but opposite sound wave, and then both that and
Speaker 1: the original sound from outside of the headphones combine and
Speaker 1: you get silence or you get no noise. I guess
Speaker 1: it depends on how you think about it. Now, this
Speaker 1: all kind of sounds simple at least in concept, but
Speaker 1: leaving it making it a reality was far from simple.
Speaker 1: Bose and his team would spend a decade and a
Speaker 1: half and more than fifty million dollars trying to figure
Speaker 1: out how to make this technology effective enough and reliable
Speaker 1: enough for the general consumer, how to have it where
Speaker 1: you know you can actually draw power from something to
Speaker 1: do this, because obviously that active part of active noise
Speaker 1: canceling requires power to work. It's not like a microphone
Speaker 1: and speaker is just going to work without any electricity.
Speaker 1: So part of this was figuring out a way of
Speaker 1: powering these headphones, preferably without requiring a wired connection. Like
Speaker 1: a wired connection might be needed for you to be
Speaker 1: able to play audio through the headset, whether that audio
Speaker 1: is coming from a communications device or the entertainment system
Speaker 1: of an airplane, but you don't want to have to
Speaker 1: draw power as well. So the goal was to create
Speaker 1: battery powered headphones, and it would take a long time
Speaker 1: for that to become a consumer product. The earliest mention
Speaker 1: I can find of a commercially available noise reduction set
Speaker 1: of headphones was in nineteen eighty nine, when Bose released
Speaker 1: the Series one Aviation headset, But even then this was
Speaker 1: a product intended for the aviation industry, as the name suggests,
Speaker 1: and it was good for reducing noise, but not eliminating it.
Speaker 1: It would take another decade for the technology to start
Speaker 1: appearing in mainstream consumer gear. In nineteen ninety nine, after
Speaker 1: Bose had been producing active noise reduction and active noise
Speaker 1: canceling headphones for the aviation industry as well as the military,
Speaker 1: the company introduced a consumer model specifically for the Hoidy
Speaker 1: toidies who were traveling first class on American airlines. The
Speaker 1: movers and shakers appeared to really like the effect, and
Speaker 1: Bose decided to introduce a consumer available version of the
Speaker 1: technology in two thousand. It was called the Quiet Comfort Series.
Speaker 1: Other companies started doing the same. Sennheiser actually created active
Speaker 1: noise canceling headphones for pilots at Luftonza in the mid
Speaker 1: nineteen eighties, so they were producing their headsets the same
Speaker 1: time BOS was, in fact, at least for the If
Speaker 1: you're looking at the first series that BOS released, Sennheiser
Speaker 1: came out with THEIRS a couple of years earlier, but
Speaker 1: Bose had had prototypes for several years at that point too,
Speaker 1: so it's kind of complicated. These days, lots of companies
Speaker 1: have noise canceling or noise reduction headphones. Apple released the
Speaker 1: Airpod's Max headset back in December twenty twenty, with a
Speaker 1: Bluetooth headset this year, so nos released its wireless noise
Speaker 1: canceling headphones, the so nos ace so the technology, even
Speaker 1: though it has its roots in the nineteen thirties, it's
Speaker 1: only been available for customers like you and me for
Speaker 1: the last couple of decades, and for those of us
Speaker 1: who are perhaps not in the tax bracket that travels
Speaker 1: first class in a regular base. It's a relatively recent development.
Speaker 1: They're pretty neat, and if you really like to focus
Speaker 1: on music or other audio, they are essential. I certainly
Speaker 1: think of them as being a necessary technology to bring
Speaker 1: with you when you're on airplane trips. It is a
Speaker 1: sanity saver, just reducing like the hum of the aircraft
Speaker 1: and all that kind of stuff. It doesn't eliminate all noise,
Speaker 1: like you could typically hear certain things outside of bands
Speaker 1: of frequencies. A lot of these are designs that you
Speaker 1: can still hear if someone talks to you. And of
Speaker 1: course there are also a lot of headsets that have
Speaker 1: like a pass through feature where instead of blocking noise,
Speaker 1: it allows external noise to reach your ears more clearly,
Speaker 1: so that you can stay aware of your environment. That way,
Speaker 1: if you're in someplace like let's say you're walking along
Speaker 1: a warehouse floor or something. You're not going to be
Speaker 1: taken by surprise by like a forklift or something like
Speaker 1: that just suddenly appearing behind you. So there are variations
Speaker 1: this technology as well, but that's how it works. I
Speaker 1: hope you found that interesting, and I hope you are
Speaker 1: all doing well, and I'll talk to you again really soon.
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