Echo!
Huseyin Bostanci/Getty Images/iStockphoto
Today we shout out our love for the ECHO! (echo echo)
Discover how these curious callbacks happen and why we hear them in some places but not others. We'll also play you the longest echo in the world and take you to an echo-proof room. Plus, an actual echo stops by to share its new podcast and we hear the answer to this Moment Of Um question: why can wild animals drink dirty water when humans need clean water?
Bonus: Learn more about the book that inspired co-host Claire to ask the question, “Is it possible for an echo to go on forever?”
Audio Transcript
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CREW: You're listening to Brains On!, where we're serious about being curious.
CREW: Brains On! is supported in part by a grant from the National Science Foundation.
MOLLY BLOOM: So Claire, you said the echo is over here somewhere?
SUBJECT 1: Yeah. There's a great echo in here. Check it out.
[YODELING]
MOLLY BLOOM: [YODELING] Ooh. Here, I'll try. [YODELING] Actually, you know what?
SUBJECT 1: Wait, what? Is someone there?
MOLLY BLOOM: Hello? I've only ever heard echoes that repeat what you say. I'm not a normal echo. I'm tired of repeating back what everyone else says.
SUBJECT 1: This is unexpected. I think it's cool when echoes repeat things. It's so echoey.
MOLLY BLOOM: It is cool, but I also have my own ideas. I've got a great recipe for slime, plenty of tips for styling stalagmites, and more. I want to share my thoughts with the world, but I'm stuck in this cave.
SUBJECT 1: Ooh, you could be the world's first Instagram-famous echo. Or what about a vlog? You could be the one and only echo on YouTube.
MOLLY BLOOM: That's a good idea, except I don't really have a physical form. I'm not sure how interesting I would be on camera.
SUBJECT 1: Oh.
MOLLY BLOOM: But what about sounds? I could record myself. I've heard about these things called podcasts. Yeah, podcasts are great. Claire and I are actually taping a podcast episode in just a bit.
SUBJECT 1: Oh, we should probably head back. It'll take some time to find our way out of this cave. But keep us posted on your show, Echo.
MOLLY BLOOM: Oh, I will. OK, Claire. So which way out?
SUBJECT 1: Take a right at the next stalactite.
[MUSIC PLAYING]
MOLLY BLOOM: You are listening to Brains On! from American Public Media. I'm Molly Bloom, and today I'm here with Claire from Vancouver Island. Welcome, Claire.
SUBJECT 1: Hi.
MOLLY BLOOM: So Claire, you sent in an excellent echo question, which we'll get to in a minute. But first, let's talk a little about echoes. Is there a place in your life right now where you get to hear echoes?
SUBJECT 1: Yes. When I go rock climbing on the big cliffs, there's lots of echoes, and I like to have fun with them.
MOLLY BLOOM: That's awesome. How long have you been rock climbing for?
SUBJECT 1: I've been rock climbing on and off since I was around six years old.
MOLLY BLOOM: Oh my goodness. That's amazing. So what kind of rock climbing do you do?
SUBJECT 1: I started off doing lots of bouldering, but now I don't do as much bouldering. And I don't rock climb as much anymore, but I use the harnesses now.
MOLLY BLOOM: And so when you are rock climbing on these cliffs-- and I'm sure they make amazing echoes-- what kind of fun do you have with echoes?
SUBJECT 1: I just say a whole bunch of words. And it's just fun to hear them come back to me.
MOLLY BLOOM: Well, echoes are very, very cool. And it's fascinating that some places have them and others don't. So what is an echo?
SUBJECT 1: Let's find out with our friend, Bob.
CREW: Hello.
MOLLY BLOOM: And a super tall mountain.
CREW: Ow. This is very high up. It's not a good sign when the birds are flying below you.
SUBJECT 1: Now, when Bob shouts, he creates sound waves.
CREW: Cheesesteak.
MOLLY BLOOM: And as those sound waves travel out from his mouth, the waves go in lots of different directions. Some waves travel into the open air, over the valleys below, and eventually hit another mountain across the way.
SUBJECT 1: Then they bounce off that mountain, travel back over the valleys, and finally reach Bob's ears.
MOLLY BLOOM: That's when he hears the echo.
CREW: Cheesesteak, cheesesteak, cheesesteak. Hah. I guess my echo likes cheesesteaks, too. I wonder if it likes yams. Yams, yams, yams.
MOLLY BLOOM: So an echo is just a sound wave that bounces off something and comes back to us a little later.
SUBJECT 1: But there's more to it than that. Sound waves bounce off all kinds of things, not just mountains. Let's say Bob is back home.
CREW: Rutabaga. Oh, my bedroom. Please excuse the mess. I wasn't expecting a podcast here today.
MOLLY BLOOM: If Bob yells here--
CREW: Rutabaga.
MOLLY BLOOM: There's no echo. Why is that? There are plenty of hard surfaces for sound to bounce off of, like that window or the wall.
CREW: Or my glass framed portrait of a wall.
MOLLY BLOOM: Wait, you have a picture of a wall on your wall?
CREW: Well, it's a different wall, Molly. Having a picture of the same wall would be silly.
MOLLY BLOOM: OK, sure. Anyway, here's the thing. In Bob's bedroom, the walls are much closer to Bob than that distant mountain across the valley was. So the sounds still bounce back at him, but they reach his ears much quicker.
CREW: Rutabaga. Huh, still no echo.
MOLLY BLOOM: If a sound bounces back to us in less than 1/10 of a second, our brains can't really tell the difference between the first sound and the sound that bounces back. So if a sound comes back very quickly, it doesn't make an echo. But it can add something else to a sound.
And that's called reverberation. That's when sound waves are reflected back to you and they build up. It can make a sound sound richer and fuller and like it lasts a little bit longer.
SUBJECT 1: Like when you're singing in the shower and the notes seem to carry.
CREW: (SINGING) When I'm singing in the shower, I've got reverberation power.
SUBJECT 1: Even though we might say this shower sounds echoey, it's not actually an echo because the shower walls are too close to you for that.
MOLLY BLOOM: For a real, honest-to-goodness echo, you need the thing your sound is bouncing off of to be a certain distance away so that your brain can tell the difference between the original sound and the echo. Typically, that distance is about 17 meters or 55 feet.
SUBJECT 1: That's about 10 feet longer than a school bus.
CREW: Oh, my shower is not that big. Even my bedroom is not that big. It's kind of small, actually.
SUBJECT 1: But what if we make Bob's bedroom bigger?
CREW: Wow, so much space now.
SUBJECT 1: You still might not hear an echo, because there are also lots of soft things that absorb sound waves, like his bed, his pillows, and curtains.
CREW: And my fuzzy velvet painting of a wall.
MOLLY BLOOM: How many pictures of walls do you have?
CREW: Nothing looks better on a wall than a wall, Molly. Walls always match walls. It's the perfect decorating trick.
SUBJECT 1: But if Bob's bigger room was suddenly empty, then you'd get your echo.
CREW: Hey, where's my furniture, furniture? Oh, an echo. Cool, cool. Walls rule, walls rule.
MOLLY BLOOM: So an echo is a sound wave that bounces off something far away.
SUBJECT 1: Usually 55 feet or more.
MOLLY BLOOM: And comes back to our ears at least 1/10 of a second after the original sound.
CREW: And pictures of walls make a great addition to any wall in your home. Thank you. Goodbye.
MOLLY BLOOM: OK, let's get back to your original question, Claire? Do you remember what you sent us?
SUBJECT 1: Yeah. I wrote, can an echo go on forever? And if I wanted it to, how and where could I do it?
MOLLY BLOOM: So how did you come up with this question, Claire?
SUBJECT 1: It was the book that my teacher read to me in grade 3. It was about a bat that went into a cave, and there was a neverending echo. And it shared stories and stuff because the bats that went in there would say them and then you could listen to them like a record.
MOLLY BLOOM: Oh, that's so cool. So do you remember the name of the book?
SUBJECT 1: It was called Silverwing.
MOLLY BLOOM: Well, thank you for sending that question, because we love that question. And it is a very interesting thought experiment. We asked Meredith Fore to weigh in. She's a physics researcher at the University of Washington.
MEREDITH FORE: The short answer is no, an echo can't go on forever. And the reason why has to do with energy. So anything that moves has energy. And so sound waves also move. They have motion. They move through the air and so they have energy as well.
MOLLY BLOOM: And that energy is key to why echoes can't go on forever.
MEREDITH FORE: Echoes, when they come back to us, are always quieter. So if I shout into a cave of-- what's up, what's up, what's up? Then the what's up that comes back to me as an echo is going to be quieter. And that's because when the waves leave my mouth and then they go hit, say, a cave wall and reflect and come back to me, that hitting of the cave wall actually makes the wave lose energy. But it also loses energy through just whatever it's traveling through.
Sound goes in all directions. So even if you're standing behind me while I'm talking, you can still hear me. So because sound is spreading out in every direction, as it spreads out and covers more and more distance, it loses energy. And it can't stay as strong and it can't stay as loud. And so the echo can't go on forever. It's always going to fade away into nothing.
MOLLY BLOOM: But if we wanted to make an echo go on and on and on and on, Meredith has an idea.
MEREDITH FORE: It would require a few, let's say, sci-fi inventions. We would need something for the echo to reflect off of that didn't take energy away from it. If I throw a ball against a wall, compare that to me throwing it against, say, a trampoline. The ball actually won't lose as much energy if I throw it against a trampoline than if I throw it against a wall.
So if you had a magic sci-fi wall that acted like a trampoline where it just threw back the ball with all the energy it originally had, then I could probably shout into that wall and the echo would come back to me with exactly as much energy. So then I could make a tunnel out of this trampoline wall. Something that we can do is make a really, really tiny tunnel, because that would prevent the sound from spreading out. And as the echo bounced back and forth, it could probably go on forever, because there is no way for it to lose energy.
MOLLY BLOOM: Wow, very cool. So Claire, what do you think of that solution?
SUBJECT 1: Yeah. It would be cool if that was actually possible to do. And it would be fun to listen in that space to the neverending echo.
MOLLY BLOOM: Yeah. So you've just got to get started on making that trampoline wall material.
SUBJECT 1: Yeah.
CREW: Brains on.
MOLLY BLOOM: Now it's time to check out the soundwaves waves created by our--
CREW: Mystery sound.
[MYSTERY SOUND]
MOLLY BLOOM: OK. So Claire, that was the mystery sound. Do you want to hear it again since it was really, really short?
SUBJECT 1: Yes.
MOLLY BLOOM: Here you go.
[MYSTERY SOUND]
All right. What is your guess?
SUBJECT 1: It sounds like water.
MOLLY BLOOM: Any other thoughts about what it might be?
SUBJECT 1: And a frog that's screaming.
MOLLY BLOOM: Yes. I like that idea. What do you think the frog is screaming about?
SUBJECT 1: Maybe it's screaming because a dam broke and then all the water is coming through. And the frog is like, get out of the way.
MOLLY BLOOM: I really like your guess. You created a whole story. I love it. We will have another chance to listen to it and guess a little later in the show. We're working on a series all about feelings.
SUBJECT 1: I feel good about that.
MOLLY BLOOM: We do, too. We're excited to answer lots of questions about feelings. And we're curious about your feelings, too. One of the feelings we're going to be talking about is nervousness. And Claire, I want to know, what does it feel like in your body when you're nervous?
SUBJECT 1: I get lots of butterflies in my stomach.
MOLLY BLOOM: Yes. I definitely know that feeling. And when I get nervous, my heart beats really fast and I feel a little shaky. And sometimes I feel cold and hot at the same time.
SUBJECT 1: We want to know how you feel when you're nervous, too.
MOLLY BLOOM: Go to brainson.org/contact to send us a short recording of what nervousness feels like to you. Or if you don't want to tell us about what nervousness feels like in your body, we'd also love to hear what happy feels like or angry or sad, too. Your choice.
SUBJECT 1: brainson.org/contact is also the place to send drawings, mystery sounds, and questions.
MOLLY BLOOM: Your questions, drawings, and mystery sounds power this show. We love checking out everything you send in, like this listener question.
SUBJECT 2: My name is Laura, and I'm from Austin, Texas. And my question is, why do we need clean water and food when other animals have dirty ones?
MOLLY BLOOM: Stick around. We'll hear the answer to that question in the Moment of Um at the end of the show. And we'll hear the latest listeners to join the Brain's honor roll.
SUBJECT 1: For any adults in earshot, this message is for you.
MOLLY BLOOM: Brains On! works really hard to strike that extra special balance of smart, fun, and funny, and we love sending new episodes your way. Your donation at brainson.org/donate helps us keep fresh, new episodes in your feed.
SUBJECT 1: And there are thank you gifts for supporters at the Brains On! website, too, like pencils or t-shirts or a beanie with a built-in headlamp.
MOLLY BLOOM: Your help means we can answer more questions, so please give at brainson.org/donate. Thank you.
SUBJECT 1: And keep listening. You're listening to Brains On! I'm Claire.
MOLLY BLOOM: And I'm Molly. And I'm Molly. Oh, fell into that old habit of repeating again. I forgot. I'm doing my own thing now.
Let's try again. And I'm an echo. Oh. Hi, echo. Nice to hear you again. I came back to share a promo for my new show. It's called the Echo Echo Go Go Show.
SUBJECT 1: Let's hear it.
MOLLY BLOOM: Pack your bags. We're going places. Traveling isn't just for people and pets. Sound travels, too. I'm Echo. And in this show, we're going on a tour. Sounds travel a little differently each place you go.
Sure, caves are great for us echoes. But so are canyons. Hello, hello. In churches, sounds bounce back quicker. The sounds that bounce back to you sound less like a separate echo and more like a reverberation.
Same in the bathroom. Wait, who said that? Is someone in here with me? Plus we'll get into what kinds of ceilings are best for carrying sounds, which materials are really cool and echoes vibes, foams and squishy stuff, and tips you can use to travel farther as a sound.
Find the Echo Echo Go Go Show every week wherever you get your podcasts. Subscribe. Interesting. Thanks for keeping us posted, Echo.
SUBJECT 1: We'll keep an eye out for your show in our podcast apps.
MOLLY BLOOM: Leave a review. Thank you, guys. Definitely. OK, so as Echo kindly just told us, echoes can go lots of places. They just can't exactly go on forever. But Brains On! producer, Marc Sanchez, looked into the longest echo we know of. He's here to help fill us in.
MARC SANCHEZ: Yup. A hearty hello to you both. Are you ready to hear a record-breaking sound?
SUBJECT 1: Oh, yeah.
MARC SANCHEZ: Awesome. This is the sound of a starter pistol, like the kind you'd see at the beginning of a 100-meter dash. And it goes on a long time. Check it out.
[GUNSHOT]
The sound is still playing underneath me. In fact, that record-setting sound goes on for 112 seconds. The longest echo before that was only 15 seconds. So this echo-- still going, by the way. This echo smashed the record by over a minute and a half. And it was all done by this guy.
TREVOR COX: Hi, I'm Trevor Cox, and I work at University of Salford, where I look into sound. And I guess most people call my subject acoustics, which is the science of sound.
MARC SANCHEZ: As an acoustic scientist, Trevor knew that 15 seconds was pretty long. But he thought there must be a place that would produce something longer, so he set out to find that place.
TREVOR COX: The old world record holder was near Glasgow in Scotland. So I went visited that. That was a mausoleum. There's no windows, and they're quite hard stone and they're relatively large, which means the sound gets held in that space a long time.
MARC SANCHEZ: Mausoleums, by the way, are special buildings and cemeteries that hold tombs. So Trevor tried to come up with other places like mausoleums. He looked for places that didn't have windows; were built out of something hard, like stone; and were very large.
TREVOR COX: And so I wrote to this group in Britain called Subterranean Britannica. And this was a group of people who loved the underground in Britain. And they said you must go to the Inchindown Oil Depot. And so that's were I went up and broke the world record.
[MUSIC PLAYING]
MARC SANCHEZ: The Inchindown Oil Depot is this secret-agent-like facility. It's literally built into the side of a mountain.
TREVOR COX: It was actually built right at the start of World War II to try and protect the Royal Navy shipping oil from being bombed.
MARC SANCHEZ: You couldn't fly planes or run a country if you didn't have oil, so this oil was very precious.
TREVOR COX: And when you go into it, you go into these underground tunnels. And in them are the most enormous concrete tanks which were built to hold all the Royal Navy shipping oil.
MARC SANCHEZ: Trevor took his starter pistol down into the oil depot and recorded the world's longest echo. He says the real key to the space is that it was made to be bombproof.
TREVOR COX: They wanted to make sure the shipping oil was safe. And so they made it out of-- well, it's essentially very, very thick concrete. And behind it is just rock, so it's incredibly solidly built. And in a room, when you lose energy is when sound bounces off the walls.
So if you go into your bedroom, you'll notice it's deader than if you go into your bathroom, for example. And that's because your bedroom's got soft things like, I don't know, your bed and your duvet and things like that, which absorb sound. Well, in this oil tank, the walls were made incredibly heavy and thick, so it just goes on and on and on.
MARC SANCHEZ: The sound eventually will die out, because it slowly loses energy bouncing off those hard walls. By the way, technically what Trevor recorded was a reverberation, since you don't hear a distinct repeat of the pistol. But the Guinness Book of World Records gave it the title Longest Echo. A lot of people use the words reverberation and echo interchangeably, even though there's a slight difference.
[SAXOPHONE PLAYING]
That's Trevor playing music by Claude Debussy on his saxophone. As you can hear, it has no reverberation or echo to it. It's what's called a dead sound. You hear it and it goes away. Now listen to how that same piece of music sounds when he played it in the Inchindown Oil Depot.
[SAXOPHONE ECHOING]
TREVOR COX: I played a little phrase from it--
[VOCALIZING]
And I thought, well, the next phrase doesn't go with what's happened in the past phrase. And that's still reverberating around the room. What am I going to do now? I just had to carry on, really, because the notes last. They blend into each other, so you actually have to think very carefully about what music you use in a space like that.
MARC SANCHEZ: Thinking about how sounds react in different spaces is how Trevor puts all these measurements to use. You know how an architect designs a building? Trevor does the same thing, but with sound. He's an acoustic architect.
When it comes to sound-- places like concert halls, offices, and classrooms. They all have a different purpose. Trevor uses measurements like reverberation or how long echos last to get an idea of how a room is going to sound when it's finished being built.
TREVOR COX: Well, the reverberation-- that's the way the sound is held in the space. It's one of the most important attributes of rooms. In a big concert hall, it would be a couple of seconds. And if you went into a cathedral, it might be 6, 7, 8 seconds. In your bedroom, maybe half a second.
So if I go and design a classroom, I will work out what the reverberation time will be and try and hit the right value to make sure the speech is good. Because you go into a really dead room, it's like talking outdoors. That's really hard work to talk, so the teacher's voice gets strained.
But if you go into a very reverberant, echoey space, then the teacher has to talk really slowly. And it's really uncomfortable, because the sound is getting all muddy. And there's obviously a sweet spot in between those two. And you're trying to find that sweet spot. So reverberation, or how echoey a space is, a crucial thing to architectural acoustics design, so very much part of my job.
MARC SANCHEZ: I want to tell you about another really cool tool Trevor uses for his job. It's a room within a room. And it does something really strange to sound. But first, I think Molly has something for you.
MOLLY BLOOM: Thank you, Marc. We'll get to that room room in just a bit. But it's time to hear that mystery sound again. Claire, are you ready?
SUBJECT 1: Yes.
MOLLY BLOOM: OK. Here it is.
[MYSTERY SOUND]
OK, Claire. Any new thoughts after hearing it again?
SUBJECT 1: No, not really. It still sounds like a frog screaming with water.
MOLLY BLOOM: OK, excellent. Well, here is the answer.
GOLDIE PHILLIPS: Hi, my name is Goldie Phillips. I am a marine mammal scientist-- specifically, I work on marine mammal sound. So the song you just heard is called the minke whale boing. The first time I heard the boing, I actually laughed because I thought it was very suitably named, because it actually sounds like a boing.
MOLLY BLOOM: So you were close. It was an animal making a noise. So it wasn't a frog. It was a whale. And it was a boing. Have you ever heard of a boing made by a whale before?
SUBJECT 1: No.
MOLLY BLOOM: Yeah, I hadn't heard of it either. So it's a very surprising sound made by a minke whale. And we're going to hear a little more from Goldie.
GOLDIE PHILLIPS: Whales in general produce low frequency sounds, or lower pitch sounds, which have the ability to travel much further underwater, generally speaking, than higher pitch sounds. So the minke whale call is a lower frequency sound. And really loud calls-- for example, the blue whales produce really, really loud calls that could be heard hundreds of kilometers away, tens of kilometers. It depends on a lot of different factors.
MOLLY BLOOM: A big reason that whale songs can travel so far is that they're low pitched sounds. And those sound waves stay stronger longer underwater. Whales also just make very loud sounds. And sound travels faster in water than it does in air.
GOLDIE PHILLIPS: So the reason why it travels so much faster under water is because water is a lot denser than air.
MOLLY BLOOM: And because sound travels so quickly in water, when Goldie and other scientists listen in on what's happening in the ocean, it can be hard to tell who's in a recording. Other whales and ships also make a lot of noise. Even crabs and fish make sounds. So for a long time, no one was sure where the minke whale boing was coming from.
GOLDIE PHILLIPS: It was actually first discovered in the 1950s. And for a long time, nobody knew what the sound was. And it wasn't until decades later, in 2002, that scientists from NOAA's Southwest Fisheries Science Center heard the sound-- and they actually used the study of sound. And they actually used it to track this sound to a minke whale. And they'd actually also discovered a minke whale breeding ground, so perhaps it's used in mating.
MOLLY BLOOM: Sometimes other unexpected sounds show up in their recordings.
GOLDIE PHILLIPS: I think the most interesting thing about recording sounds underwater is the types of sounds that you get. So one interesting thing that I learned that I thought was quite amusing at the time is that manatees-- so they actually fart a lot. And you can detect those underwater. So you'll be surprised at the things you can pick up underwater.
MOLLY BLOOM: If you want to know more about manatee farts, and other animals gas-passing habits, check out our episode on animal farts. It's called "A Mighty Wind."
[MUSIC PLAYING]
OK, let's get back to longest echo record holder, Trevor Cox.
SUBJECT 1: Marc told us how Trevor works with sound as an acoustic architect.
MOLLY BLOOM: And that means using a very special tool for measuring sound.
MARC SANCHEZ: That's right. It's called an anechoic chamber. Anechoic is a way of saying without echo and chamber is just another word for room, so a room without echo. Remember that record-breaking echo we heard earlier?
[GUNSHOT]
Well, here's that same sound in an anechoic chamber. Listen close. Not exactly 112 seconds, right? That's the point. Anechoic chambers are echo squashers. Here, listen again. It's hardly anything. Trevor recorded that starter pistol sound in the anechoic chamber, where he teaches at the University of Salford.
TREVOR COX: Yeah, so an anechoic chamber is the most incredible space you'd probably ever get into. First of all, it's a weird space, because you usually end up going-- in ours at Salford, you go through three sets of doors to actually get into the place to start with. And that's to try and make sure no sound gets in from the outside world. So it's a room within a room. And then when you get into the middle of it, what you do is you look around, and what you see are these foam wedges all around you.
MARC SANCHEZ: And these foam wedges are really thick. They're about two feet deep, a little bit longer than your average cat. And they are everywhere-- on the walls, on the ceiling, even on the floor. And they all stick out like a bunch of jagged, pointy teeth. This foam is what absorbs the sound.
It's so quiet in there, in fact, if you hold your breath, you can hear the blood pumping through your body. Even more interesting, according to Trevor, is the way people hear sound in an anechoic chamber as opposed to a regular room. Take my voice. You probably think you're just hearing my voice come straight from my mouth.
TREVOR COX: As you talk to someone in a room, you hear the sound direct from that person's mouth to your ears. But actually, you get loads of reflections from the walls, the floor, and the ceiling. And they have a huge effect on the sound you get. And you don't really realize that until you go into an anechoic chamber, because you go in there and everyone sounds a bit quiet. And if you do something like burst a balloon in an anechoic chamber, it's very disappointing, because a lot of the boom of a balloon burst is actually coming from a room. It's actually the energy of the room adding to the energy of the balloon.
MARC SANCHEZ: This is why the loud sound of that starter pistol we're used to hearing sounds so quiet and short. Anechoic chambers help to measure the characteristics of a sound. So let's say you record a waiter in a restaurant.
MOLLY BLOOM: Party of six? We have a table right over here for you.
MARC SANCHEZ: There are all sorts of other noises that might be picked up. Maybe there's a car honking outside, customers are enjoying their meals, laughing it up, maybe the chef has a cold and is sneezing. And the voice itself will be bouncing off surfaces all over the room, changing how we hear it.
MOLLY BLOOM: Party of six? We have a table right over here for you.
MARC SANCHEZ: Recording and measuring a sound in a room with no reverberation or echo allows us to understand how that same sound might act in a different space.
TREVOR COX: That's how you design a room to make the sound within it better. So that might be designing a concert hall so the orchestra sounds more beautiful-- or it might be something as simple as making a classroom where you can hear the teacher and the teacher can hear the pupils, and therefore, learning happens.
CREW: Brains on, brains on, brains on.
MOLLY BLOOM: An echo is a sound wave that bounces off something and comes back to your ear at least a tenth of a second later.
SUBJECT 1: Sound waves lose energy as they travel and bounce off things, so echoes can't go on forever.
MOLLY BLOOM: Sound travels even faster in water than it does in air. It turns out the ocean is a very noisy place.
SUBJECT 1: An acoustic architect checks how sound bounces around to help design how a room or building sounds.
MOLLY BLOOM: An anechoic chamber is a special room built to have no echoes. That's it for this episode.
SUBJECT 1: Brains On! is produced by Molly Bloom, Marc Sanchez, and Sanden Totten.
MOLLY BLOOM: A bellowed hello from our fellow, Menaka Wilhelm.
MENAKA WILHELM: Hello. Do I hear an echo?
MOLLY BLOOM: Not now, Maneka. I'm doing my own thing now, remember? We had production help from Christina Lopez and Jacqueline Kim and engineering help from Veronica Rodriguez, Rick Jurkovich, and Corey Chapel. Special thanks to Barb and Randall Mendel, Eric Wrangham, Rosie DuPont, and Dana Kobinger.
SUBJECT 1: And a big thank you to all the listeners out there. Your questions, answers, mystery sounds, and drawings fuel Brains On!
MOLLY BLOOM: Brains On! is a nonprofit public radio podcast. Your support at brainson.org/donate also helps keep this show going. Thank you. Now, before we go, it's time for a moment of um.
SUBJECT 2: Why do we need clean water and food when other animals have dirty ones?
YVONNE DREXLER: I'm Yvonne Drexler, an Associate Professor of Immunology at the Veterinary College of Western University of Health Sciences in Pomona. And I teach veterinary students and research how the immune system of animals works and what can go wrong with it. Actually, animals do also need clean food and water.
So if animals drink, for example, out of a mud puddle, it might appear dirty because of the kicked up sand that's in there. But it might not have germs, which is the main reason they can actually get sick from it. And so when I go hiking in the mountains with my dogs, I don't let them drink the water, because it can have germs and they can get, for example, diarrhea from it.
So some germs are parasites, bacteria, and viruses. Or if your cats and dogs can also hunt their own prey or drink water from other sources outside, they can get worms which will grow inside their intestines and take their nutrition. And that's why we have to go regularly to the veterinarian and get our cats or dogs dewormed.
And then humans are just more aware and careful about what they eat and drink. And so hopefully, you all wash your hands before you eat. And on the other hand, there are a lot of wild animals that are drinking from water that's maybe in one location that they go to often. And so they get a bit more resistance to the bacteria and viruses that are in there because they encounter them a lot and it's the same germs.
But then when a new germ shows up in their water, they can still get sick because they are not used to it. But you might not notice it, because animals actually also hide when they get sick. And we don't always see the signs of them being sick. Then there are animals that eat mostly rotten food, and we call them scavengers, like hyenas, vultures, or coyotes. And they have evolved such that they can eat this food without getting sick, actually.
MOLLY BLOOM: This list is like a cool, clean glass of water on a hot day. It's the Brain's Honor Roll. These are the amazing listeners who keep us going with their questions, ideas, mystery sounds, drawings, and high-fives.
[LISTING HONOR ROLL]
SUBJECT 1: Thanks for listening.
CREW: Brains On! is supported in part by a grant from the National Science Foundation.
MOLLY BLOOM: So Claire, you said the echo is over here somewhere?
SUBJECT 1: Yeah. There's a great echo in here. Check it out.
[YODELING]
MOLLY BLOOM: [YODELING] Ooh. Here, I'll try. [YODELING] Actually, you know what?
SUBJECT 1: Wait, what? Is someone there?
MOLLY BLOOM: Hello? I've only ever heard echoes that repeat what you say. I'm not a normal echo. I'm tired of repeating back what everyone else says.
SUBJECT 1: This is unexpected. I think it's cool when echoes repeat things. It's so echoey.
MOLLY BLOOM: It is cool, but I also have my own ideas. I've got a great recipe for slime, plenty of tips for styling stalagmites, and more. I want to share my thoughts with the world, but I'm stuck in this cave.
SUBJECT 1: Ooh, you could be the world's first Instagram-famous echo. Or what about a vlog? You could be the one and only echo on YouTube.
MOLLY BLOOM: That's a good idea, except I don't really have a physical form. I'm not sure how interesting I would be on camera.
SUBJECT 1: Oh.
MOLLY BLOOM: But what about sounds? I could record myself. I've heard about these things called podcasts. Yeah, podcasts are great. Claire and I are actually taping a podcast episode in just a bit.
SUBJECT 1: Oh, we should probably head back. It'll take some time to find our way out of this cave. But keep us posted on your show, Echo.
MOLLY BLOOM: Oh, I will. OK, Claire. So which way out?
SUBJECT 1: Take a right at the next stalactite.
[MUSIC PLAYING]
MOLLY BLOOM: You are listening to Brains On! from American Public Media. I'm Molly Bloom, and today I'm here with Claire from Vancouver Island. Welcome, Claire.
SUBJECT 1: Hi.
MOLLY BLOOM: So Claire, you sent in an excellent echo question, which we'll get to in a minute. But first, let's talk a little about echoes. Is there a place in your life right now where you get to hear echoes?
SUBJECT 1: Yes. When I go rock climbing on the big cliffs, there's lots of echoes, and I like to have fun with them.
MOLLY BLOOM: That's awesome. How long have you been rock climbing for?
SUBJECT 1: I've been rock climbing on and off since I was around six years old.
MOLLY BLOOM: Oh my goodness. That's amazing. So what kind of rock climbing do you do?
SUBJECT 1: I started off doing lots of bouldering, but now I don't do as much bouldering. And I don't rock climb as much anymore, but I use the harnesses now.
MOLLY BLOOM: And so when you are rock climbing on these cliffs-- and I'm sure they make amazing echoes-- what kind of fun do you have with echoes?
SUBJECT 1: I just say a whole bunch of words. And it's just fun to hear them come back to me.
MOLLY BLOOM: Well, echoes are very, very cool. And it's fascinating that some places have them and others don't. So what is an echo?
SUBJECT 1: Let's find out with our friend, Bob.
CREW: Hello.
MOLLY BLOOM: And a super tall mountain.
CREW: Ow. This is very high up. It's not a good sign when the birds are flying below you.
SUBJECT 1: Now, when Bob shouts, he creates sound waves.
CREW: Cheesesteak.
MOLLY BLOOM: And as those sound waves travel out from his mouth, the waves go in lots of different directions. Some waves travel into the open air, over the valleys below, and eventually hit another mountain across the way.
SUBJECT 1: Then they bounce off that mountain, travel back over the valleys, and finally reach Bob's ears.
MOLLY BLOOM: That's when he hears the echo.
CREW: Cheesesteak, cheesesteak, cheesesteak. Hah. I guess my echo likes cheesesteaks, too. I wonder if it likes yams. Yams, yams, yams.
MOLLY BLOOM: So an echo is just a sound wave that bounces off something and comes back to us a little later.
SUBJECT 1: But there's more to it than that. Sound waves bounce off all kinds of things, not just mountains. Let's say Bob is back home.
CREW: Rutabaga. Oh, my bedroom. Please excuse the mess. I wasn't expecting a podcast here today.
MOLLY BLOOM: If Bob yells here--
CREW: Rutabaga.
MOLLY BLOOM: There's no echo. Why is that? There are plenty of hard surfaces for sound to bounce off of, like that window or the wall.
CREW: Or my glass framed portrait of a wall.
MOLLY BLOOM: Wait, you have a picture of a wall on your wall?
CREW: Well, it's a different wall, Molly. Having a picture of the same wall would be silly.
MOLLY BLOOM: OK, sure. Anyway, here's the thing. In Bob's bedroom, the walls are much closer to Bob than that distant mountain across the valley was. So the sounds still bounce back at him, but they reach his ears much quicker.
CREW: Rutabaga. Huh, still no echo.
MOLLY BLOOM: If a sound bounces back to us in less than 1/10 of a second, our brains can't really tell the difference between the first sound and the sound that bounces back. So if a sound comes back very quickly, it doesn't make an echo. But it can add something else to a sound.
And that's called reverberation. That's when sound waves are reflected back to you and they build up. It can make a sound sound richer and fuller and like it lasts a little bit longer.
SUBJECT 1: Like when you're singing in the shower and the notes seem to carry.
CREW: (SINGING) When I'm singing in the shower, I've got reverberation power.
SUBJECT 1: Even though we might say this shower sounds echoey, it's not actually an echo because the shower walls are too close to you for that.
MOLLY BLOOM: For a real, honest-to-goodness echo, you need the thing your sound is bouncing off of to be a certain distance away so that your brain can tell the difference between the original sound and the echo. Typically, that distance is about 17 meters or 55 feet.
SUBJECT 1: That's about 10 feet longer than a school bus.
CREW: Oh, my shower is not that big. Even my bedroom is not that big. It's kind of small, actually.
SUBJECT 1: But what if we make Bob's bedroom bigger?
CREW: Wow, so much space now.
SUBJECT 1: You still might not hear an echo, because there are also lots of soft things that absorb sound waves, like his bed, his pillows, and curtains.
CREW: And my fuzzy velvet painting of a wall.
MOLLY BLOOM: How many pictures of walls do you have?
CREW: Nothing looks better on a wall than a wall, Molly. Walls always match walls. It's the perfect decorating trick.
SUBJECT 1: But if Bob's bigger room was suddenly empty, then you'd get your echo.
CREW: Hey, where's my furniture, furniture? Oh, an echo. Cool, cool. Walls rule, walls rule.
MOLLY BLOOM: So an echo is a sound wave that bounces off something far away.
SUBJECT 1: Usually 55 feet or more.
MOLLY BLOOM: And comes back to our ears at least 1/10 of a second after the original sound.
CREW: And pictures of walls make a great addition to any wall in your home. Thank you. Goodbye.
MOLLY BLOOM: OK, let's get back to your original question, Claire? Do you remember what you sent us?
SUBJECT 1: Yeah. I wrote, can an echo go on forever? And if I wanted it to, how and where could I do it?
MOLLY BLOOM: So how did you come up with this question, Claire?
SUBJECT 1: It was the book that my teacher read to me in grade 3. It was about a bat that went into a cave, and there was a neverending echo. And it shared stories and stuff because the bats that went in there would say them and then you could listen to them like a record.
MOLLY BLOOM: Oh, that's so cool. So do you remember the name of the book?
SUBJECT 1: It was called Silverwing.
MOLLY BLOOM: Well, thank you for sending that question, because we love that question. And it is a very interesting thought experiment. We asked Meredith Fore to weigh in. She's a physics researcher at the University of Washington.
MEREDITH FORE: The short answer is no, an echo can't go on forever. And the reason why has to do with energy. So anything that moves has energy. And so sound waves also move. They have motion. They move through the air and so they have energy as well.
MOLLY BLOOM: And that energy is key to why echoes can't go on forever.
MEREDITH FORE: Echoes, when they come back to us, are always quieter. So if I shout into a cave of-- what's up, what's up, what's up? Then the what's up that comes back to me as an echo is going to be quieter. And that's because when the waves leave my mouth and then they go hit, say, a cave wall and reflect and come back to me, that hitting of the cave wall actually makes the wave lose energy. But it also loses energy through just whatever it's traveling through.
Sound goes in all directions. So even if you're standing behind me while I'm talking, you can still hear me. So because sound is spreading out in every direction, as it spreads out and covers more and more distance, it loses energy. And it can't stay as strong and it can't stay as loud. And so the echo can't go on forever. It's always going to fade away into nothing.
MOLLY BLOOM: But if we wanted to make an echo go on and on and on and on, Meredith has an idea.
MEREDITH FORE: It would require a few, let's say, sci-fi inventions. We would need something for the echo to reflect off of that didn't take energy away from it. If I throw a ball against a wall, compare that to me throwing it against, say, a trampoline. The ball actually won't lose as much energy if I throw it against a trampoline than if I throw it against a wall.
So if you had a magic sci-fi wall that acted like a trampoline where it just threw back the ball with all the energy it originally had, then I could probably shout into that wall and the echo would come back to me with exactly as much energy. So then I could make a tunnel out of this trampoline wall. Something that we can do is make a really, really tiny tunnel, because that would prevent the sound from spreading out. And as the echo bounced back and forth, it could probably go on forever, because there is no way for it to lose energy.
MOLLY BLOOM: Wow, very cool. So Claire, what do you think of that solution?
SUBJECT 1: Yeah. It would be cool if that was actually possible to do. And it would be fun to listen in that space to the neverending echo.
MOLLY BLOOM: Yeah. So you've just got to get started on making that trampoline wall material.
SUBJECT 1: Yeah.
CREW: Brains on.
MOLLY BLOOM: Now it's time to check out the soundwaves waves created by our--
CREW: Mystery sound.
[MYSTERY SOUND]
MOLLY BLOOM: OK. So Claire, that was the mystery sound. Do you want to hear it again since it was really, really short?
SUBJECT 1: Yes.
MOLLY BLOOM: Here you go.
[MYSTERY SOUND]
All right. What is your guess?
SUBJECT 1: It sounds like water.
MOLLY BLOOM: Any other thoughts about what it might be?
SUBJECT 1: And a frog that's screaming.
MOLLY BLOOM: Yes. I like that idea. What do you think the frog is screaming about?
SUBJECT 1: Maybe it's screaming because a dam broke and then all the water is coming through. And the frog is like, get out of the way.
MOLLY BLOOM: I really like your guess. You created a whole story. I love it. We will have another chance to listen to it and guess a little later in the show. We're working on a series all about feelings.
SUBJECT 1: I feel good about that.
MOLLY BLOOM: We do, too. We're excited to answer lots of questions about feelings. And we're curious about your feelings, too. One of the feelings we're going to be talking about is nervousness. And Claire, I want to know, what does it feel like in your body when you're nervous?
SUBJECT 1: I get lots of butterflies in my stomach.
MOLLY BLOOM: Yes. I definitely know that feeling. And when I get nervous, my heart beats really fast and I feel a little shaky. And sometimes I feel cold and hot at the same time.
SUBJECT 1: We want to know how you feel when you're nervous, too.
MOLLY BLOOM: Go to brainson.org/contact to send us a short recording of what nervousness feels like to you. Or if you don't want to tell us about what nervousness feels like in your body, we'd also love to hear what happy feels like or angry or sad, too. Your choice.
SUBJECT 1: brainson.org/contact is also the place to send drawings, mystery sounds, and questions.
MOLLY BLOOM: Your questions, drawings, and mystery sounds power this show. We love checking out everything you send in, like this listener question.
SUBJECT 2: My name is Laura, and I'm from Austin, Texas. And my question is, why do we need clean water and food when other animals have dirty ones?
MOLLY BLOOM: Stick around. We'll hear the answer to that question in the Moment of Um at the end of the show. And we'll hear the latest listeners to join the Brain's honor roll.
SUBJECT 1: For any adults in earshot, this message is for you.
MOLLY BLOOM: Brains On! works really hard to strike that extra special balance of smart, fun, and funny, and we love sending new episodes your way. Your donation at brainson.org/donate helps us keep fresh, new episodes in your feed.
SUBJECT 1: And there are thank you gifts for supporters at the Brains On! website, too, like pencils or t-shirts or a beanie with a built-in headlamp.
MOLLY BLOOM: Your help means we can answer more questions, so please give at brainson.org/donate. Thank you.
SUBJECT 1: And keep listening. You're listening to Brains On! I'm Claire.
MOLLY BLOOM: And I'm Molly. And I'm Molly. Oh, fell into that old habit of repeating again. I forgot. I'm doing my own thing now.
Let's try again. And I'm an echo. Oh. Hi, echo. Nice to hear you again. I came back to share a promo for my new show. It's called the Echo Echo Go Go Show.
SUBJECT 1: Let's hear it.
MOLLY BLOOM: Pack your bags. We're going places. Traveling isn't just for people and pets. Sound travels, too. I'm Echo. And in this show, we're going on a tour. Sounds travel a little differently each place you go.
Sure, caves are great for us echoes. But so are canyons. Hello, hello. In churches, sounds bounce back quicker. The sounds that bounce back to you sound less like a separate echo and more like a reverberation.
Same in the bathroom. Wait, who said that? Is someone in here with me? Plus we'll get into what kinds of ceilings are best for carrying sounds, which materials are really cool and echoes vibes, foams and squishy stuff, and tips you can use to travel farther as a sound.
Find the Echo Echo Go Go Show every week wherever you get your podcasts. Subscribe. Interesting. Thanks for keeping us posted, Echo.
SUBJECT 1: We'll keep an eye out for your show in our podcast apps.
MOLLY BLOOM: Leave a review. Thank you, guys. Definitely. OK, so as Echo kindly just told us, echoes can go lots of places. They just can't exactly go on forever. But Brains On! producer, Marc Sanchez, looked into the longest echo we know of. He's here to help fill us in.
MARC SANCHEZ: Yup. A hearty hello to you both. Are you ready to hear a record-breaking sound?
SUBJECT 1: Oh, yeah.
MARC SANCHEZ: Awesome. This is the sound of a starter pistol, like the kind you'd see at the beginning of a 100-meter dash. And it goes on a long time. Check it out.
[GUNSHOT]
The sound is still playing underneath me. In fact, that record-setting sound goes on for 112 seconds. The longest echo before that was only 15 seconds. So this echo-- still going, by the way. This echo smashed the record by over a minute and a half. And it was all done by this guy.
TREVOR COX: Hi, I'm Trevor Cox, and I work at University of Salford, where I look into sound. And I guess most people call my subject acoustics, which is the science of sound.
MARC SANCHEZ: As an acoustic scientist, Trevor knew that 15 seconds was pretty long. But he thought there must be a place that would produce something longer, so he set out to find that place.
TREVOR COX: The old world record holder was near Glasgow in Scotland. So I went visited that. That was a mausoleum. There's no windows, and they're quite hard stone and they're relatively large, which means the sound gets held in that space a long time.
MARC SANCHEZ: Mausoleums, by the way, are special buildings and cemeteries that hold tombs. So Trevor tried to come up with other places like mausoleums. He looked for places that didn't have windows; were built out of something hard, like stone; and were very large.
TREVOR COX: And so I wrote to this group in Britain called Subterranean Britannica. And this was a group of people who loved the underground in Britain. And they said you must go to the Inchindown Oil Depot. And so that's were I went up and broke the world record.
[MUSIC PLAYING]
MARC SANCHEZ: The Inchindown Oil Depot is this secret-agent-like facility. It's literally built into the side of a mountain.
TREVOR COX: It was actually built right at the start of World War II to try and protect the Royal Navy shipping oil from being bombed.
MARC SANCHEZ: You couldn't fly planes or run a country if you didn't have oil, so this oil was very precious.
TREVOR COX: And when you go into it, you go into these underground tunnels. And in them are the most enormous concrete tanks which were built to hold all the Royal Navy shipping oil.
MARC SANCHEZ: Trevor took his starter pistol down into the oil depot and recorded the world's longest echo. He says the real key to the space is that it was made to be bombproof.
TREVOR COX: They wanted to make sure the shipping oil was safe. And so they made it out of-- well, it's essentially very, very thick concrete. And behind it is just rock, so it's incredibly solidly built. And in a room, when you lose energy is when sound bounces off the walls.
So if you go into your bedroom, you'll notice it's deader than if you go into your bathroom, for example. And that's because your bedroom's got soft things like, I don't know, your bed and your duvet and things like that, which absorb sound. Well, in this oil tank, the walls were made incredibly heavy and thick, so it just goes on and on and on.
MARC SANCHEZ: The sound eventually will die out, because it slowly loses energy bouncing off those hard walls. By the way, technically what Trevor recorded was a reverberation, since you don't hear a distinct repeat of the pistol. But the Guinness Book of World Records gave it the title Longest Echo. A lot of people use the words reverberation and echo interchangeably, even though there's a slight difference.
[SAXOPHONE PLAYING]
That's Trevor playing music by Claude Debussy on his saxophone. As you can hear, it has no reverberation or echo to it. It's what's called a dead sound. You hear it and it goes away. Now listen to how that same piece of music sounds when he played it in the Inchindown Oil Depot.
[SAXOPHONE ECHOING]
TREVOR COX: I played a little phrase from it--
[VOCALIZING]
And I thought, well, the next phrase doesn't go with what's happened in the past phrase. And that's still reverberating around the room. What am I going to do now? I just had to carry on, really, because the notes last. They blend into each other, so you actually have to think very carefully about what music you use in a space like that.
MARC SANCHEZ: Thinking about how sounds react in different spaces is how Trevor puts all these measurements to use. You know how an architect designs a building? Trevor does the same thing, but with sound. He's an acoustic architect.
When it comes to sound-- places like concert halls, offices, and classrooms. They all have a different purpose. Trevor uses measurements like reverberation or how long echos last to get an idea of how a room is going to sound when it's finished being built.
TREVOR COX: Well, the reverberation-- that's the way the sound is held in the space. It's one of the most important attributes of rooms. In a big concert hall, it would be a couple of seconds. And if you went into a cathedral, it might be 6, 7, 8 seconds. In your bedroom, maybe half a second.
So if I go and design a classroom, I will work out what the reverberation time will be and try and hit the right value to make sure the speech is good. Because you go into a really dead room, it's like talking outdoors. That's really hard work to talk, so the teacher's voice gets strained.
But if you go into a very reverberant, echoey space, then the teacher has to talk really slowly. And it's really uncomfortable, because the sound is getting all muddy. And there's obviously a sweet spot in between those two. And you're trying to find that sweet spot. So reverberation, or how echoey a space is, a crucial thing to architectural acoustics design, so very much part of my job.
MARC SANCHEZ: I want to tell you about another really cool tool Trevor uses for his job. It's a room within a room. And it does something really strange to sound. But first, I think Molly has something for you.
MOLLY BLOOM: Thank you, Marc. We'll get to that room room in just a bit. But it's time to hear that mystery sound again. Claire, are you ready?
SUBJECT 1: Yes.
MOLLY BLOOM: OK. Here it is.
[MYSTERY SOUND]
OK, Claire. Any new thoughts after hearing it again?
SUBJECT 1: No, not really. It still sounds like a frog screaming with water.
MOLLY BLOOM: OK, excellent. Well, here is the answer.
GOLDIE PHILLIPS: Hi, my name is Goldie Phillips. I am a marine mammal scientist-- specifically, I work on marine mammal sound. So the song you just heard is called the minke whale boing. The first time I heard the boing, I actually laughed because I thought it was very suitably named, because it actually sounds like a boing.
MOLLY BLOOM: So you were close. It was an animal making a noise. So it wasn't a frog. It was a whale. And it was a boing. Have you ever heard of a boing made by a whale before?
SUBJECT 1: No.
MOLLY BLOOM: Yeah, I hadn't heard of it either. So it's a very surprising sound made by a minke whale. And we're going to hear a little more from Goldie.
GOLDIE PHILLIPS: Whales in general produce low frequency sounds, or lower pitch sounds, which have the ability to travel much further underwater, generally speaking, than higher pitch sounds. So the minke whale call is a lower frequency sound. And really loud calls-- for example, the blue whales produce really, really loud calls that could be heard hundreds of kilometers away, tens of kilometers. It depends on a lot of different factors.
MOLLY BLOOM: A big reason that whale songs can travel so far is that they're low pitched sounds. And those sound waves stay stronger longer underwater. Whales also just make very loud sounds. And sound travels faster in water than it does in air.
GOLDIE PHILLIPS: So the reason why it travels so much faster under water is because water is a lot denser than air.
MOLLY BLOOM: And because sound travels so quickly in water, when Goldie and other scientists listen in on what's happening in the ocean, it can be hard to tell who's in a recording. Other whales and ships also make a lot of noise. Even crabs and fish make sounds. So for a long time, no one was sure where the minke whale boing was coming from.
GOLDIE PHILLIPS: It was actually first discovered in the 1950s. And for a long time, nobody knew what the sound was. And it wasn't until decades later, in 2002, that scientists from NOAA's Southwest Fisheries Science Center heard the sound-- and they actually used the study of sound. And they actually used it to track this sound to a minke whale. And they'd actually also discovered a minke whale breeding ground, so perhaps it's used in mating.
MOLLY BLOOM: Sometimes other unexpected sounds show up in their recordings.
GOLDIE PHILLIPS: I think the most interesting thing about recording sounds underwater is the types of sounds that you get. So one interesting thing that I learned that I thought was quite amusing at the time is that manatees-- so they actually fart a lot. And you can detect those underwater. So you'll be surprised at the things you can pick up underwater.
MOLLY BLOOM: If you want to know more about manatee farts, and other animals gas-passing habits, check out our episode on animal farts. It's called "A Mighty Wind."
[MUSIC PLAYING]
OK, let's get back to longest echo record holder, Trevor Cox.
SUBJECT 1: Marc told us how Trevor works with sound as an acoustic architect.
MOLLY BLOOM: And that means using a very special tool for measuring sound.
MARC SANCHEZ: That's right. It's called an anechoic chamber. Anechoic is a way of saying without echo and chamber is just another word for room, so a room without echo. Remember that record-breaking echo we heard earlier?
[GUNSHOT]
Well, here's that same sound in an anechoic chamber. Listen close. Not exactly 112 seconds, right? That's the point. Anechoic chambers are echo squashers. Here, listen again. It's hardly anything. Trevor recorded that starter pistol sound in the anechoic chamber, where he teaches at the University of Salford.
TREVOR COX: Yeah, so an anechoic chamber is the most incredible space you'd probably ever get into. First of all, it's a weird space, because you usually end up going-- in ours at Salford, you go through three sets of doors to actually get into the place to start with. And that's to try and make sure no sound gets in from the outside world. So it's a room within a room. And then when you get into the middle of it, what you do is you look around, and what you see are these foam wedges all around you.
MARC SANCHEZ: And these foam wedges are really thick. They're about two feet deep, a little bit longer than your average cat. And they are everywhere-- on the walls, on the ceiling, even on the floor. And they all stick out like a bunch of jagged, pointy teeth. This foam is what absorbs the sound.
It's so quiet in there, in fact, if you hold your breath, you can hear the blood pumping through your body. Even more interesting, according to Trevor, is the way people hear sound in an anechoic chamber as opposed to a regular room. Take my voice. You probably think you're just hearing my voice come straight from my mouth.
TREVOR COX: As you talk to someone in a room, you hear the sound direct from that person's mouth to your ears. But actually, you get loads of reflections from the walls, the floor, and the ceiling. And they have a huge effect on the sound you get. And you don't really realize that until you go into an anechoic chamber, because you go in there and everyone sounds a bit quiet. And if you do something like burst a balloon in an anechoic chamber, it's very disappointing, because a lot of the boom of a balloon burst is actually coming from a room. It's actually the energy of the room adding to the energy of the balloon.
MARC SANCHEZ: This is why the loud sound of that starter pistol we're used to hearing sounds so quiet and short. Anechoic chambers help to measure the characteristics of a sound. So let's say you record a waiter in a restaurant.
MOLLY BLOOM: Party of six? We have a table right over here for you.
MARC SANCHEZ: There are all sorts of other noises that might be picked up. Maybe there's a car honking outside, customers are enjoying their meals, laughing it up, maybe the chef has a cold and is sneezing. And the voice itself will be bouncing off surfaces all over the room, changing how we hear it.
MOLLY BLOOM: Party of six? We have a table right over here for you.
MARC SANCHEZ: Recording and measuring a sound in a room with no reverberation or echo allows us to understand how that same sound might act in a different space.
TREVOR COX: That's how you design a room to make the sound within it better. So that might be designing a concert hall so the orchestra sounds more beautiful-- or it might be something as simple as making a classroom where you can hear the teacher and the teacher can hear the pupils, and therefore, learning happens.
CREW: Brains on, brains on, brains on.
MOLLY BLOOM: An echo is a sound wave that bounces off something and comes back to your ear at least a tenth of a second later.
SUBJECT 1: Sound waves lose energy as they travel and bounce off things, so echoes can't go on forever.
MOLLY BLOOM: Sound travels even faster in water than it does in air. It turns out the ocean is a very noisy place.
SUBJECT 1: An acoustic architect checks how sound bounces around to help design how a room or building sounds.
MOLLY BLOOM: An anechoic chamber is a special room built to have no echoes. That's it for this episode.
SUBJECT 1: Brains On! is produced by Molly Bloom, Marc Sanchez, and Sanden Totten.
MOLLY BLOOM: A bellowed hello from our fellow, Menaka Wilhelm.
MENAKA WILHELM: Hello. Do I hear an echo?
MOLLY BLOOM: Not now, Maneka. I'm doing my own thing now, remember? We had production help from Christina Lopez and Jacqueline Kim and engineering help from Veronica Rodriguez, Rick Jurkovich, and Corey Chapel. Special thanks to Barb and Randall Mendel, Eric Wrangham, Rosie DuPont, and Dana Kobinger.
SUBJECT 1: And a big thank you to all the listeners out there. Your questions, answers, mystery sounds, and drawings fuel Brains On!
MOLLY BLOOM: Brains On! is a nonprofit public radio podcast. Your support at brainson.org/donate also helps keep this show going. Thank you. Now, before we go, it's time for a moment of um.
SUBJECT 2: Why do we need clean water and food when other animals have dirty ones?
YVONNE DREXLER: I'm Yvonne Drexler, an Associate Professor of Immunology at the Veterinary College of Western University of Health Sciences in Pomona. And I teach veterinary students and research how the immune system of animals works and what can go wrong with it. Actually, animals do also need clean food and water.
So if animals drink, for example, out of a mud puddle, it might appear dirty because of the kicked up sand that's in there. But it might not have germs, which is the main reason they can actually get sick from it. And so when I go hiking in the mountains with my dogs, I don't let them drink the water, because it can have germs and they can get, for example, diarrhea from it.
So some germs are parasites, bacteria, and viruses. Or if your cats and dogs can also hunt their own prey or drink water from other sources outside, they can get worms which will grow inside their intestines and take their nutrition. And that's why we have to go regularly to the veterinarian and get our cats or dogs dewormed.
And then humans are just more aware and careful about what they eat and drink. And so hopefully, you all wash your hands before you eat. And on the other hand, there are a lot of wild animals that are drinking from water that's maybe in one location that they go to often. And so they get a bit more resistance to the bacteria and viruses that are in there because they encounter them a lot and it's the same germs.
But then when a new germ shows up in their water, they can still get sick because they are not used to it. But you might not notice it, because animals actually also hide when they get sick. And we don't always see the signs of them being sick. Then there are animals that eat mostly rotten food, and we call them scavengers, like hyenas, vultures, or coyotes. And they have evolved such that they can eat this food without getting sick, actually.
MOLLY BLOOM: This list is like a cool, clean glass of water on a hot day. It's the Brain's Honor Roll. These are the amazing listeners who keep us going with their questions, ideas, mystery sounds, drawings, and high-fives.
[LISTING HONOR ROLL]
SUBJECT 1: Thanks for listening.
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