First Ad<\/strong><\/h2>\n\n\n\nSeason 2, Episode 18\u2026 Screaming Babies, Noise Canceling, and You.<\/p>\n\n\n\n
In April 1978, MIT professor Amar Bose was flying back home to Boston from a business meeting in Switzerland. Yes, that would be Bose, as in the Bose Corporation, the audio-equipment company he\u2019d founded in 1964, when he was 35 years old.<\/p>\n\n\n\n
Now, by the mid seventies, plenty of airplanes had sound systems for passengers. Kind of. They were these long, flexible plastic tubes that plugged into audio sockets on the armrest. And on your end, they had foam earplugs. I mean, technically you could hear music, but it had all the audio fidelity of listening to AM radio over the phone.<\/p>\n\n\n\n
But on this flight, things would be different.<\/p>\n\n\n\n
Ursula: In 1978, we were in Europe and on the way back. For the first time, they had actual headphones instead of just those tubes. And so he was pretty excited about that because it\u2014oh my God, thank God. Finally, something that might sound, you know, decent.<\/p>\n\n\n\n
That\u2019s his widow, Ursula Boltzhauser, in a 2018 Bose video. <\/p>\n\n\n\n
GAUGER: And airlines were\u2014at the time, in 1978\u2014just in the process of switching over to what looked like Walkman, early Walkman headphones, because the Walkman had just been introduced and it was now possible to manufacture those headphones for very, very low costs, so the airlines were adopting. <\/p>\n\n\n\n
And that\u2019s Dan Gauger, one of the two engineers who founded and built the company\u2019s noise-canceling headphone division.<\/p>\n\n\n\n
GAUGER: And Dr. Bose was excited. For once, he thought he\u2019d have great music on that flight. <\/p>\n\n\n\n
Now, I will say this for the old flexible-plastic-tube contraption: Those foam earplugs at least plugged your ears. They shut out a lot of the airplane noise.<\/p>\n\n\n\n
GAUGER: But the Walkman headphones didn\u2019t. And by the time he turned the music up so loud that he could enjoy it, it was not enjoyable, and the noise was interfering. <\/p>\n\n\n\n
Ursula And put them on and realized that, well, with these things on your ears, the sound from the airplane came in much, much more. And he was very disappointed. <\/p>\n\n\n\n
\u201cAvengers\u201d-style hero music<\/em><\/p>\n\n\n\nSo on that fateful day, Dr. Bose stood up at his seat, shook his fist at the heavens, and proclaimed, \u201cI\u2026am\u2026BOSE! One of the greatest acoustical minds alive! Solving the problem of listening to music on airplanes is within my grasp!\u201d <\/p>\n\n\n\n
OK, those may not have been his exact words. He may not have actually stood up. Or shook his fist. Or actually said anything at all. <\/p>\n\n\n\n
But here\u2019s what he did do:<\/p>\n\n\n\n
Ursula: So he took out a pad and pen and started writing equations. By the time we reached Boston, he had a which he thought might work.<\/p>\n\n\n\n
A concept for headphones that would literally subtract background noise from what you hear. <\/p>\n\n\n\n
Here, in essence, was his idea:<\/p>\n\n\n\n
GAUGER: So sound is\u2014what is sound? It\u2019s very small, rapid variations in the pressure of air. Slight deviations from the atmosphere at your local atmospheric pressure. <\/p>\n\n\n\n
Pogue: OK. <\/p>\n\n\n\n
GAUGER: And, you know, for the sort of sound what we are most effective at canceling, it\u2019s varying, you know, one to two or three hundred times a second. <\/p>\n\n\n\n
POGUE: Okay. <\/p>\n\n\n\n
GAUGER: High pressure, low pressure, high pressure, low pressure. Now, you\u2019re wearing an ear cup. Some of that outside sound gets to the inside of the ear cup. So when there\u2019s a high pressure inside your cup, there\u2019s more air molecules inside the ear cup. <\/p>\n\n\n\n
We add microphones on the outside that sense the noise as it arrives at the headphone. And we figure out how to generate a signal to go into the speaker inside the headphone. <\/p>\n\n\n\n
We move the speaker back to make more room for the ear, and lower the pressure. <\/p>\n\n\n\n
RULE: The outside mic gives you a look ahead. You don\u2019t have to wait until it shows up at the microphone before you say, \u201cah, I see this thing and I now need to do the opposite.\u201d You\u2019re like, \u201cWell, no, I saw it coming, because I have a microphone facing outward. And as I can do the math fast enough, then I know what\u2019s going to hit the inside of my ear before it gets there, right?\u201d<\/p>\n\n\n\n
That voice belongs to John Rule, a Bose engineer who specializes in noise cancellation.<\/p>\n\n\n\n
So let\u2019s see. When the external microphone senses a sound wave coming into the headphones, the little speaker inside the earcup literally moves. <\/em>It moves back a minuscule fraction of an inch, in a minuscule fraction of a second, to make more space inside the earcup, thereby lowering <\/em>the air pressure for that millisecond, therefore erasing the effect of the sound wave that came in from the plane noise around you. It cancels <\/em>the noise.<\/p>\n\n\n\nSo what\u2019s it sound like?<\/p>\n\n\n\n
RULE: For somebody who\u2019s never had experience with this, you\u2019d say, oh, it turns everything down by a factor of ten. We\u2019re closing in on, you know, 50x, 80x reduction\u2014so you could say, hey, everything gets quieter. <\/p>\n\n\n\n
So your first experience is like, \u201cwow, everything got quieter!\u201d You know, it doesn\u2019t make the world silent, because that\u2019s really hard, right? It\u2019s nowhere near as annoying as it was when it was full volume, but, you know, it\u2019s now\u2014it\u2019s like a whisper, but it\u2019s kind of still there. <\/p>\n\n\n\n
It\u2019s hard to demonstrate the effect on a podcast. I mean, I have no idea what you\u2019re listening on right now! Is it headphones? Earbuds? Are you in your car? Listening through your phone\u2019s speaker? Tablet? Laptop? TV? <\/p>\n\n\n\n
But let\u2019s try. Here is an actual recording that Bose engineers made on an actual plane\u2014not a flight I myself was on, although I swear, this same screaming baby somehow winds up on every other flight i take:<\/p>\n\n\n\n
Baby before.aiff<\/em><\/p>\n\n\n\nAnd now, the same scene with noise cancellation\u2014an actual recording, with no doctoring or funny business:<\/p>\n\n\n\n
Baby after.aiff<\/em><\/em><\/p>\n\n\n\nPogue: How come there aren\u2019t certain times, certain frequencies, where the noise canceling sounds take out some of the music you\u2019re hearing?<\/p>\n\n\n\n
GAUGER: Well, the answer to that is\u2014we\u2019re not just trying to create silence. We\u2019re servo controlling, or feedback controlling, to make the sound at the entrance to your ear be the music. The music is the command input to the feedback system. <\/p>\n\n\n\n
Pogue: Okay. So if there\u2019s a certain frequency that is being canceled that is also a note in the music, you\u2019ll just double that sound output?<\/p>\n\n\n\n
GAUGER: Probably too simplistically\u2014yes. Yeah. <\/p>\n\n\n\n
Pogue: You must be writhing inside. Oh, my God, this guy\u2019s consumer-friendly description of something that took us 30 years to do\u2026 <\/p>\n\n\n\n
We interrupt this podcast to offer an apologetic production note.<\/p>\n\n\n\n
Between the time we did this interview and the time of editing, the fantastic-sounding recording of ME, my end of the conversation, somehow got lost to the internet ether. We did have a backup of the interview\u2014the audio from the Zoom meeting where the interview took place\u2014so that\u2019s what you\u2019re hearing every time I speak in these interview excerpts. <\/p>\n\n\n\n
I know, it sounds like doo-doo. Which is especially embarrassing because this is an episode ABOUT AUDIO.<\/p>\n\n\n\n
OK, moving on. <\/p>\n\n\n\n
We were talking about doing noise cancellation in real time. <\/p>\n\n\n\n
I mean, we\u2019re describing how noise canceling works as though it\u2019s, you know, \u201cOh, you just pump out air pressure out of phase hundreds of times a second, and voila!\u201d But I hope you can appreciate what an astonishingly difficult feat that is to pull off. <\/p>\n\n\n\n
GAUGER: Imagine the surface of the ocean or even just of a pond, on a windy day with all the waves. The peaks of the waves are like high sound pressure\u2014and the valleys are like low sound pressure. Try to imagine taking a plunger to make more waves. Stand in one spot in the lake and make more waves and try to make the surface of the lake smooth. <\/p>\n\n\n\n
With sound, it\u2019s even\u2014it\u2019s more complicated. It\u2019s three-dimensional. <\/p>\n\n\n\n
As Bose executives in that 2018 video recall:<\/p>\n\n\n\n
Speaker 11: There were many people in the company who would say, \u201cWhy are you wasting your time on this technology?\u201d<\/p>\n\n\n\n
Speaker 3: \u201cThe concept that you could cancel sound with sound was the most ridiculous. It\u2019s like putting somebody on the moon for me, right?\u201d<\/p>\n\n\n\n
Now here, I must insist that we pause the proceedings to make a very important point. <\/p>\n\n\n\n
There are long sound waves, and short sound waves. <\/p>\n\n\n\n
RULE: Low frequencies\u2014if you think about the wavelength\u2014low frequencies like 100 hertz, the wavelength is 12 feet, right? <\/p>\n\n\n\n
I\u2019m going to play you a 100-hertz sound, meaning 100 vibrations per second. Those waves reaching your ear right now? 12 feet long.<\/p>\n\n\n\n
100hz tone.<\/em><\/p>\n\n\n\nRULE: When you go to a kilohertz, it\u2019s about a foot. <\/p>\n\n\n\n
Now here\u2019s a one-kilohertz sound\u20141000 sound waves a second, ten times faster, each one a foot long.<\/p>\n\n\n\n
1 khz tone. <\/em><\/p>\n\n\n\nRULE: And when you go to ten kilohertz, it\u2019s about an inch, roughly speaking. Right? <\/p>\n\n\n\n
And here comes a 10-khz sound. It\u2019s really high, and the sound waves are really short. If you\u2019re over 50 or listening on cruddy speaker, you may barely be able to hear it at all.<\/p>\n\n\n\n
10 khz tone.<\/em><\/p>\n\n\n\nRULE: Higher and higher frequencies, you\u2019re getting to smaller and smaller waves. And all of a sudden, the length between the the microphone and your eardrum becomes significant. <\/p>\n\n\n\n
Pogue: Oh, my gosh. I see. And that\u2019s why they always say these things work best on low rumbles or, you know, medium airplane hiss.<\/p>\n\n\n\n
GAUGER: You know, that\u2019s\u2014that\u2019s a key part of it. Cancellation needs to have long wavelengths\u2014more slowly changing sound\u2014because we\u2019re always chasing the sound that\u2019s gone into your ear. We can\u2019t cancel at ten kilohertz when the wavelengths get so short. <\/p>\n\n\n\n
That was a lot to absorb, but here\u2019s the bottom line: These headphones do great at canceling low sounds, like the dull roar of plane engines or A\/C units or subway rumbles. They do lousy at blocking high-pitched sounds\u2014like screaming babies on planes. <\/p>\n\n\n\n
And for that reason, all the fancy math and electronics and speaker movement we\u2019ve been talking about are responsible for only half <\/em>the quietness you detect when you put on these headphones. To keep out the high pitches, they use an entirely different system\u2014one that\u2019s almost embarrassingly low-tech.<\/p>\n\n\n\nGAUGER: This is actually something that\u2019s annoyed me for, you know, as I\u2019ve watched cancellation become a real big thing in the consumer space\u2014people use \u201ccancellation\u201d to refer to anything that lowers the noise that\u2019s going into your ear. <\/p>\n\n\n\n
Pogue: Right. <\/p>\n\n\n\n
GAUGER: And that\u2019s not the case. Cancellation is when you use an out-of- phase sound to cancel the sound you don\u2019t want. There\u2019s also attenuation\u2014the physical blocking of the sound. And a well-designed headphone uses both of those. The physical blocking at high frequencies and cancellation at low frequencies. <\/p>\n\n\n\n
Pogue: So the fact that they\u2019re earcups pressed against your head, that\u2019s not just for comfort or good music sound\u2014that gets you part of the way toward lowering the volume outside. <\/p>\n\n\n\n
GAUGER: That lowers the high frequency hiss. It doesn\u2019t do much against low frequency rumble, particularly if you designed the headphones to be comfortable to wear. <\/p>\n\n\n\n
You know, I have worn things in research labs that have, you know, incredible pressure against the side of your head, and you want to scream after 30 seconds. And those will block, you know, a fair amount of sound, but they still can\u2019t block the low frequencies very effectively. So the challenge is how to put low frequency cancellation, high frequency attenuation\u2014passive attenuation\u2014and comfort together in a small headphone that people can wear and carry and use and enjoy. <\/p>\n\n\n\n
If you watch YouTube videos about noise-canceling headphones, you often hear the term active <\/em>noise cancellation, or ANC. That <\/em>is just the electronic part, the part that blocks the low frequencies. That\u2019s the part you can turn on or off with a switch. <\/p>\n\n\n\nAs for the part where the headphones just entomb your ears inside padded cups\u2014that\u2019s passive<\/em> noise reduction.<\/p>\n\n\n\nPogue: So, John, you indicated that by the time you get to the higher frequency sounds, these pressure waves are only an inch big. <\/p>\n\n\n\n
Pogue: Does that mean, then, that it\u2019s a matter of physics and not technology? In other words, no matter how far we go into the future with \u2026miniaturization and faster processors\u2014is it possible you could ever do high frequencies as well as we do low ones?<\/p>\n\n\n\n
RULE: It is hard\u2014you know, we\u2019re working on it. You know, there are other types of sensors we could imagine. We\u2019ve looked at sensing vibrations on your skin directly. Not sure what that would look like in a headphone. <\/p>\n\n\n\n
Pogue: Wow. <\/p>\n\n\n\n
GAUGER: A lot of people have commented over the years that if you sit in some environment with a lot of rumble, like an airplane or a bus or a train, you put on the headphones, it\u2019s like you hear the voices around you better with the headphones. <\/p>\n\n\n\n
Pogue: Yeah. <\/p>\n\n\n\n
GAUGER: And that\u2019s because this region where it\u2019s active cancellation at low frequencies and passive reduction in high frequencies, they don\u2019t stitch together completely smoothly and flat. There\u2019s a range of frequencies in the middle where there\u2019s a lot of voice energy. Where we\u2019re least effective when you put these things together. And so the headphones knock the rumble down but let some of the voices through. <\/p>\n\n\n\n
OK, so back to our history lesson: Dr. Bose hired my guest Dan Gauger to develop these headphones in 1980. By 1986, they had a prototype. <\/p>\n\n\n\n
GAUGER: But we had some, you know, challenges in front of us. You know, Bose at the time was a much smaller company. We\u2019d never designed a headphone. When we looked at the costs of trying to create a product, it was way out of range of anything that could be a consumer product. And we got involved in the Voyager project in \u201886. <\/p>\n\n\n\n
Ah, yes, the Voyager project. It was an attempt to make the first non-stop, around-the-world flight in an airplane. A specially designed, weird-looking, super-light, carbon-fiber airplane. <\/p>\n\n\n\n
Narr: The voyager begins to lumber down the long runway. Its attempt to fly around the world is beginning. <\/p>\n\n\n\n
Anyway, because the plane was built to weigh as little as possible, it had no <\/em>insulation. It was incredibly loud inside. <\/p>\n\n\n\nThe pilots would be sitting right next to deafening engines; the flight engineers calculated that by the end of the nine-day trip, the pilots would have lost 30% of their hearing. Probably not something they looked forward to.<\/p>\n\n\n\n
Dan Gauger cold-called the Voyager team and invited them to try out his noise-canceling prototype. The two pilots, Dick Rutan and Jeanna Yeagar, tried out the headphones during their test flights; they were sold. On the day of takeoff, they became the first pilots ever to wear noise-canceling headphones. <\/p>\n\n\n\n
Ultimately, the Voyager flight was successful\u2014they flew around the world in what amounted to a flying fuel tank, breaking all kinds of records. Here\u2019s how CNN covered the landing:<\/p>\n\n\n\n
CNN: \u201c10 feet\u20266 feet.\u201d \u201cDown on the ground.\u201d \u201cYeah-hah!\u201d \u201cIt\u2019s down!\u201d \u201cWelcome home.\u201d \u201cA feat no one ever thought was possible has occurred here at the Edwards Air Force Base.\u201d<\/p>\n\n\n\n
Unfortunately, the headphones conked out partway through the flight, as depicted in the 1992 TV documentary show Frontiers of Flight:<\/p>\n\n\n\n