Original artwork by  Jon McCormack

Original artwork by Jon McCormack

Our world is filled with sound. It exists in even the quietest corners of the planet. But what happens when all that sound is taken away? What is silence? There are very few places on Earth where silence actually exists, but in this episode, Dallas experiences it for himself thanks to a special room called an anechoic chamber. How do our brains process the complete nothingness of silence? Find out as Dallas locks himself alone inside the chamber. Featuring David Alvord and Nick Breen from the Georgia Tech Research Institute.


Day Sleepers by Cubby
Innervisible (Chroma Variant) by A.M. Architect
Chapter 3 by A New Normal
Cry by Laxcity
Home Sweet Home by Chad Lawson
Pools of Light by A.M. Architect
Ebb and Flow (feat. Matt Huber) by Josh Hoover
Frame by Frame by Rad Wolf

20k is produced out of the studios of Defacto Sound and hosted by Dallas Taylor.


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View Transcript ▶︎

[SFX: Anechoic Chamber Recording]

Dallas: Okay. I’m rolling. You’re going to shut the doors and leave me in here for a little while.

David: That’s right. You may want to point your mic over here because they are heavy-duty reinforced doors. Have fun!

Nick: Have fun!

[SFX: Anechoic Chamber Recording - Door close sound]

You’re listening to Twenty Thousand Hertz. I’m Dallas Taylor.

[SFX: Anechoic Chamber Recording]

Dallas: Okay. Now I’m inside this thing by myself. Oh! They just shut off the lights. Excellent.

You just heard me being locked into an anechoic chamber. It’s a room designed to completely isolate sound. I went in to answer a seemingly simple question. What is silence?

[SFX: Busy, noisy city ambience]

When you think of silence, maybe you picture getting away from the city and going deep into nature.

[SFX: City ambience fades away into a gentle, quiet forest. A very gentle rustling of leaves and birds are heard]

The constant noise of the city fades away, replaced only by birdsong and the gentle rush of wind through leaves. It’s refreshing and calm... But it’s not silence.

[SFX: Nature ambiences crescendo, then cut off abruptly. An uncomfortable, silent pause begins.]

Silence is the complete and total lack of sound. And to many who’ve experienced it, silence isn’t relaxing or calm. It’s terrifying. Some say it can even drive you crazy.

[SFX - Anechoic Chamber Recording]

Dallas: Hey, I’m Dallas.

Nick: I’m Nick, nice to meet you.

Dallas: I’m sorry. Just ignore all this stuff.

Nick: Oh on, that’s fine.

[SFX - Anechoic Chamber Recording fades down]

Nick: We have a large anechoic chamber. It’s, I think, 24 feet tall or so and maybe another 20 or so foot square. It’s a really big room. It’s covered in foam that makes it anechoic so there’s no reflections.

That’s Nick Breen from the Georgia Tech Research Institute. I recently visited the institute to see if the rumors about silence were true. The thing is, quiet places are relatively easy to find on Earth. But silence is incredibly rare. Luckily for me, the institute has two very special rooms where silence exists.

[music in]

David: My name is David Alvord. I’m a senior research engineer with the Georgia Tech Research Institute. We use anechoic chambers to find out what is the true sound generated by an object or an article under test without contamination from any exterior sources, whether it’s environmental or reflections generated in a room.

Nick: You can close the door to the room so there's no sound from the outside world getting in. Then, it's basically the only sounds are what you're producing in the room and because the walls are covered in foam, there won't be any echoes or anything like that because they're treated. If you're just silent, you don't hear anything.

In many ways, anechoic chambers are designed with the same goals in mind as recording studios. Albeit to a much more controlled degree. In both cases, it’s all about minimizing reflections and exterior sound sources.

[music out]

David: The three of us are currently sitting in a standard office, no particularly special acoustic treatments in here. We have carpet on the floor and traditional office acoustic tiles in the ceiling, but beyond that, it's rigid walls and everything.

So what you're hearing from us just conversationally right now is actually the direct path or me speaking at the microphone or speaking at Dallas, but also all of the reflections and multipath that we have going on in this room.

We’re almost always surrounded by acoustic reflections, whether we realize it or not. But that doesn’t happen in an anechoic chamber.

[music in]

Nick: When you make sound... your alarm clock makes sound, it's creating pressure vibrations in the air where it is.

[SFX: Alarm clock buzzing]

Nick: Those pressure vibrations propagate outwards. As molecules hit other molecules, eventually, it comes to your ears. That's what you hear and that's how you hear noise.

David: Very often these days, you see a lot more new constructions are based off of more open floor plans. With the open floor plans, your sound travels a lot more and also with the reflections, those travel much further. Basically, you're having a lot more destructive interference or reflections interfering with your main discussion than you do in maybe a smaller room or in a bedroom where you may have, for example, your bed that has a comforter and that is a soft surface that helps what's called attenuate the sound, which effectively deadens some of the reflections in a similar way that the anechoic chamber does.

I have to admit, I was nervous about being locked in the anechoic chamber alone. We’re used to hearing sound all the time. Would I lose it when all that of is taken away? Before I could find out, I wanted to know why anechoic chambers and acoustic research are important.

[music out]

With our world getting noisier and noisier, acoustic research is more relevant now than ever. We need to understand how sound works in order to make our world sound better. Researchers use more than just anechoic chambers to experiment with all that noise.

David: The opposite of an anechoic chamber, anechoic meaning an echo, like no echo is literally an echo chamber or a reverberation chamber. Typically, these are exactly the opposite of what you might picture for an anechoic chamber. An anechoic chamber is covered in foam wedges and it has a lot of soft treatments inside. Reverb chambers typically have nothing but solid surfaces. If my office was a reverb chamber, we would open the door, walk in. The first step that Dallas takes would just echo off the wall for an extremely long time.

[SFX: Footstep with a really long, cavernous reverb]

Typically, what they look for in reverb chambers are stuff like… Here's a vacuum. You're going to put a vacuum in there. A vacuum is loud.

[SFX: Vacuum sound effect with that same reverb]

Then, what they may do is they may put a treatment in there. They may put some new kind of attenuating service in there or they may put a muffler on part of the vacuum itself.

[SFX: Vacuum sound getting dampened/attenuated]

Researchers use these different chambers to isolate the huge amount of variables that are out in the world. This way they can focus in on just the aspects of one particular sound.

But sound research goes a lot farther than just making our world sound better. It also makes us safer.

[music in]

There are some types of sounds that can have a dangerous impact on our health, and the risk of exposure to these sounds is higher than ever. One example of this is infrasound.

The lowest human frequency that we can technically hear is 20 hertz. The wavelengths of sound below that threshold are too long for our eardrums to vibrate, so we can’t hear them. But that doesn’t mean we can’t feel it.

David: Sound waves around five and six hertz actually resonate with your organs of your body. If you go to a beach and there are offshore wind farms, depending on what speed the blades are turning, they may generate sound waves, infrasonic waves that actually resonate your intestines and make you feel sick, like you're going to throw up.

That’s just one of the many ways infrasound can affect you. These sound waves can also travel farther than audible frequencies, meaning it’s harder to get away from them.

[music out]

David: Like with any sound source, anything can be lethal. There are audible sounds that, sufficiently loud, can kill a person. If you were next to the engines at the base of the Saturn V during liftoff and you weren't completely destroyed by the plume that was generated through the engines themselves, [SFX - Intense, stylized rocket liftoff sound] the amplitude of the sound in the audible range is so high that it would rupture your eardrums, cause brain bleeding and you would likely die from the sound exposure alone.

Similar things can happen in the infrasonic range where if infrasound amplitudes are sufficiently high, it can negatively react with your body and cause any number of health issues.

And because you can’t hear it, you may not even know it’s happening.

David: The longer I work in the field of acoustics... you begin to realize how much noise pollution there really is out there. You start to pick up on how loud background stuff that we take for granted every day actually is.

[SFX: AC units, traffic, office walla, etc.]

Whether it's your AC unit, whether it's people driving or whether it's other people in open office plan is. You start to realize, once sound is taken away…

[SFX: the cacophony drifts away to silence]

...the absence of sound in an anechoic chamber... you don't really hear anything. Then, you start to layer all that sound back in. You realize just how loud even the most acoustically-treated open spaces really are.

[music in]

So what happens when you take all that sound away? I learned a lot about the research done in anechoic chambers, but to really understand what silence is like I had to experience it for myself. Does silence really sound like nothing? What does our brain do without audio input? And most importantly, does silence make you lose your mind? I’ll find out, in a moment.

[music out]


[music in]

If you’ve heard about anechoic chambers in the past, it’s likely you’ve also heard about all the strange things a person can experience when in one... Things like being able to hear the blood pumping through your veins, [SFX - blood pumping] or high pitched noises when there shouldn’t be any [SFX - high pitched insects, stylized]. Some even say anechoic chambers cause hallucinations and can drive a person crazy.

[SFX: heavy breathing, all sounds cacophony and fade away]

It’s all really fascinating. But is it true? Well, I’ll use myself as a guinea pig.

[music out]

David: Now, we're standing in our control room. It's a very lab-type space, but the main function of our control room is to be able to run our anechoic chambers and acquire the data inside the chambers without us having to physically be inside of there, contaminating the data being recorded.

This room is not treated whatsoever because this is just where we are running the experiments. We're making extra sure that none of this noise bleeds into the two chambers we're about to go into.

[music in]

The Georgia Tech Research Institute has two anechoic chambers. The chambers work by isolating the room from any exterior sound sources and using giant foam wedges for absorbing reflections in the room.

Nick: Not only do they absorb sound by themselves, but their shape is uniquely designed to help attenuate noise. Higher frequency noise, instead of reflecting off of these wedges, it will actually bounce between them because of their triangular shapes. By the time it reflects back out, the sound is so reduced that that's what makes these room anechoic.

David: These are called melamine wedges. If you look closely at them, you can see they're very porous, of varying porosities.The porosity is different throughout because the different-sized pores captures different frequencies. If you have one standardized pore throughout this entire wedge, it would be very effective at one frequency, but anything between the harmonics and the primary fundamental frequency, it would be garbage. It'd be as if it wasn't there.

[music out]

The acoustic treatments in these chambers are tested far more rigorously than the treatments you’ll find in a traditional recording studio. To properly research the physical properties of sound, David and Nick need an extremely controlled environment. It’s a whole different field from sound design, and other creative uses of sound. When talking about creative sound design of any sort, that’s more in the psychoacoustic category.

David: Psychoacoustics is the study of acoustic waves interacting with a perceived receiver, so a human. Usually, that's where we get more subjective so we don't say the SPL or the sound pressure level of a room. This is where you start to use your terminology such as loudness, timbre, tinny, stuff that are much more subjective, but reflect the listening experience that you are trying to drive home.

Dallas: Would you say that we're a psychoacoustic show?

David: I would say some of the editing you have done definitely was intended to illicit psychoacoustic responses in your listeners.

Dallas: Okay. As much as I'm trying to get the physics, I'm not there yet.

David: [laughing] You’re getting there.

Alright, I understood how an anechoic chamber works. I also understood what they’re used for. But now, it’s time to go in.

[SFX: Door opening, entering chamber]

David: Alright, after you. Oh is the… light’s on?

Nick: Well half the fun is turning out the lights.

David: Oh then you hit the lights switch then. Give him the big reveal.

[SFX: Door closing, background ambience goes quiet]

David: Alright go ahead.

Dallas: Oh my goodness. Again this looks incredibly dangerous.

David: That’s what a lot of people say. Yeah, give that a good shove.

The contrast between the noisy control room and the silence of the chamber was intense. The first thing I noticed was the complete lack of reflections.

Dallas: The most jarring part of it is when you’re facing away from me...

David: Okay.

Dallas: ...because there’s like no reflection coming back to me. It’s really weird.

I asked David to help me illustrate the effect through counting. He started by facing me, but slowly turned 360 degrees towards the wall and back. Listen to how the frequencies of his voice get absorbed by the treatment in the chamber. There is absolutely no eq or processing on this. This is the raw recording.

David: One, two, three, four, five [voice becomes muffled and attenuated as he turns], six, seven, eight, nine, ten [voice becomes full as he turns back forward], eleven, twelve, thirteen, fourteen, fifteen.

Again, we’re not putting any sort of filter on his voice. That’s how it naturally sounded in the room to my ears. The upper frequencies and reflections are being completely absorbed by the foam. Anyway, the time had come for me to be locked in the chamber alone. There would be no sound except for what I made myself. How long could I handle that nothingness?


[SFX: Chamber door closing]

Dallas: Okay, so I’m in a… what you call a cherry picker, which is a motorized thing. It has a little cart. It’s kinda what people use when they’re doing electrical work on electrical lines outside. So they have me two stories above the surface. Which, the surface isn’t really much of a surface because it is a bunch of wedge foam. And it is very quiet in here… With no noise, and no light. It’s pretty odd to hear… nothing.

Dallas: So people say that you can go crazy in these things, but I don’t believe them.

Dallas: Alright I think I’ve been in here for about 7 or 8 minutes. One thing that people talk about when they go into anechoic chambers is pressure. So I do feel pressure, which is odd because there’s nothing that would actually be putting pressure on my ear drums. But having no sound at all feels… feels a little bit like being… like under the water far enough where it starts to hurt your ears. That’s kinda what it feels like.

Dallas: And I hear a high-pitched… I don’t know if I’d say I hear it, but I perceive a high pitched noise. It’s gotta be something that’s just in my brain or ear. It’s like my brain is interpreting it as audible but I don’t know if it is. But I definitely hear a very high pitched, almost like high noise. It’s not a single tone, but it’s like high pitched noise.

Dallas: So another phenomenon, is that you start to hear your internal organs more the longer you’re in here. I’m starting to hear my heartbeat. I can’t even breathe through my nose because it’s so loud.

Dallas: When everything goes away, for now ten minutes, I guess my brain is searching for sound. And so it’s boosting everything in that auditory sense as much as it can. I guess it would be like closing your eyes and kind of seeing spots and stuff. It’s like your brain is trying to get visual input. It’s kind of doing the same thing with audio, like it wants audio input. So I’m hearing… or I’m perceiving that I’m hearing things. That’s the weird thing. I know I’m not hearing anything, but my brain is interpreting some sort of signal that I am hearing something.

Dallas: As much as I thought that this would be kind of a going crazy experience, it hasn’t really been like that for me. Now that I’ve been in here for 30 minutes… I don’t know. I think I’d want to stay in here overnight. I’m kind of tired now. Alright, I think this is it, I’m going to have them open up the door.

[SFX: Chamber door opening]

David: He’s alive!

Dallas: I survived.

Nick: He survived.

Dallas: I have to be honest I probably could have just kept going and just taken a nap.

David: I was about to say, the right people could settle in there and just like, “this is pretty good.”

[SFX: Recording dips down under music coming in]

[music in]

So I didn’t go crazy inside the anechoic chamber. The silence was actually in some ways comforting. It could be because I’m used to working in acoustically treated rooms. But, that said, there were some distinct experiences in that silence that could be really uncomfortable. For me, silence didn’t sound like nothing. It sounded like pressure. It sounded like my heartbeat. It sounded like high-pitched insects as my brain struggled to interpret anything. Our brains are simply not wired for true silence.

Thousands of years ago, people lived in nature. The only sounds they heard were from the natural environment around them. Now our world is filled with devices that make noise - machinery, computers, traffic…. Research into sound is so vital to our health and happiness.

David: It's interesting because sound is one of our five senses and yet, it's so commonly overlooked. It's omnipresent and everybody gets exposed to sound in whatever their unique situations are. Whether it's in the different types of areas I've been exposed to whether it's architectural or psycho or aero or just general acoustics, every one of those touches on each one of our lives. I know when I am exposed to sound less, like if it's properly treated, I feel more at ease. I don't feel so anxious.

[music out]

If I had one takeaway to leave you with, it would be this. Appreciate the quiet times and places in your life. They really are increasingly hard to find. As for silence... If you have the opportunity to experience it, I don’t know if I would recommend it. While I didn’t go crazy, you never know what you might hear, or see, in that complete nothingness…

[SFX - the sound of blood pumping, high-pitched insects, and heavy breathing slowly sneak up]

[music in]


Twenty Thousand Hertz is produced out of the studios of Defacto Sound. A sound design team that works in foam covered rooms and makes television, film, and games sound incredible. Find out more at defactosound dot com.

This episode was written and produced by Colin DeVarney… and me, Dallas Taylor. With help from Sam Schneble. It was edited, sound designed, and mixed by Colin DeVarney.

The music in this episode is from our friends at Musicbed. Go listen at Musicbed dot com.

Thanks to our guests David Alvord and Nick Breen from the Georgia Tech Research Institute…

Dallas: So David, last question. What is your favorite sound in the world?

David: I think my favorite sound is actually ambient wilderness noise. It’s very calming and it kind of pulls me back to where we all came from.

What’s your favorite sound in the world? You can tell us through our website, facebook, twitter, or by writing hi at 20 kay dot org. Thanks for listening.

[music out]

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