[RADIOLAB INTRO]

JAD ABUMRAD: Hello, I'm Jad.

ROBERT KRULWICH: I'm Robert.

JAD: This is Radiolab, the podcast.

ROBERT: Yeah.

JAD: So today, slightly offbeat exploration of acoustic warfare. And we're gonna do it by looking at the famous ...

ROBERT: Do you know this story?

JAD: I—I know what we're doing.

ROBERT: Should I remind you of the story?

JAD: I've heard the phrase "Walls of Jericho," and I know nothing else about it.

ROBERT: Because it's most famous as a song. [singing] "Joshua fought the Battle of Jericho, Jericho, Jericho. Joshua fought the Battle of Jericho, and the walls came tumbling down."

JAD: Don't know it. No idea.

ROBERT: You don't know that?

JAD: No. Before my time. Really before my time.

ROBERT: [laughs] No, no, no, no. It's a Negro spiritual, it's a Black American spiritual.

[ARCHIVE CLIP: [singing]]

JAD: Wow!

ROBERT: Yeah. Anyways ...

JAD: So tell us the story so we can get started.

ROBERT: Well, as you know, the Hebrew people crossed the Red Sea, and then wandered around in the desert for a while.

JAD: We'll just say I knew that.

ROBERT: 40 years.

JAD: 40 years?

ROBERT: And now we're up to—we're almost into the promised land, but there is this city called Jericho.

JAD: Who is inside Jericho?

ROBERT: Well, the Jerichoans.

JAD: Really?

ROBERT: The Jerichoans. I don't know much about them, actually.

JAD: Why aren't they friendly? Are they against God?

ROBERT: No, they're just—I think they have all these 40,000 people showed up and were like, "Hey, who are these people? Get them out of here!"

JAD: So they were just looking after their property.

ROBERT: I suppose. Or maybe they just didn't like what they saw.

JAD: Okay.

ROBERT: "Now Jericho ..."

JAD: You're reading now.

ROBERT: I'm reading from the Bible.

JAD: Okay.

ROBERT: "Now Jericho was tightly shut because of the sons of Israel. So I guess God says you've gotta take Jericho. Maybe that was the—I'm a little fuzzy here on the cause of the thing.

JAD: It had to be done.

ROBERT: Had to be done. However, now quoting the Bible, "Jericho was tightly shut."

JAD: Because it had a wall.

ROBERT: Yeah.

JAD: So read the part about how they knock down the wall.

ROBERT: Here's the formula. From the mouth of God.

JAD: Mm-hmm.

ROBERT: "And you shall march around the city, all the men of war circling the city once, and you shall do so for six days. And on the seventh day, you shall march around the city seven times and seven priests shall carry seven trumpets of ram's horns." It's a shofar, actually, is a ram's horn. "And the priests shall blow the trumpets, and it shall be the wall of the city will fall flat down."

JAD: And they do this with seven trumpets, you say.

ROBERT: Yes.

JAD: All right. So here we go. The question we have then for this podcast is: what would it really take ...

[ARCHIVE CLIP, singing: Joshua fought the Battle of Jericho ...]

JAD: ... to do this?

ROBERT: Yeah.

JAD: I'm talking without God. Only puny physics.

DAVID LUBMAN: Here are your headphones. Independent left and right volume control. Should be fairly comfortable.

ROBERT: Is it just in principle possible for sound to blow down a wall?

JAD: That's our question. We actually called up a guy who's thought about this.

ROBERT: Yeah.

DAVID LUBMAN: I'm an acoustical consultant.

ROBERT: David Lubman ...

JAD: ... is his name.

DAVID LUBMAN: And an acoustical scientist. And if you think about the nature of sound, it's a fluctuating pressure.

JAD: He explained that when sound hits an object, the waves actually push the object, but also pull at it.

DAVID LUBMAN: Many times per second.

JAD: And theoretically, he says, if you can get enough of those pushes and pulls on the wall ...

DAVID LUBMAN: Eventually, it'll begin to crumble.

JAD: So the first question he asked, naturally is: what kind of wall are we dealing with?

DAVID LUBMAN: Well, looking at the construction of Bronze Age walls in the Middle East, they were mud brick walls.

ROBERT: The question then was: how much sound would be necessary, what volume, to topple a wall like that?

JAD: Yeah.

ROBERT: And he came up with a number. This is a technical number for the strength of the sound.

DAVID LUBMAN: You would need to produce 177 dB.

ROBERT: 177 decibels.

DAVID LUBMAN: Yes.

JAD: That would knock down the wall?

DAVID LUBMAN: Yes.

JAD: How many decibels, just for scale, is my voice right now, roughly?

DAVID LUBMAN: Your voice is probably about 60 or 65 decibels.

JAD: Oh! So we're already a third of the way there just talking?

DAVID LUBMAN: Well, no.

[ARCHIVE CLIP, singing: Joshua, Jericho, ba-doo-wah.]

JAD: And here's where the issue starts. Sound doesn't add up the way that you would think.

DAVID LUBMAN: And there's the rub. Assume that your voice level was 60 decibels. In order to get 70 decibels, you would have to produce 10 times as much power.

JAD: This didn't make much sense to us, until we ended up doing what he did and recruiting ...

DAVID LUBMAN: Some experienced shofar blowers from synagogues.

ROBERT: We went up to All Souls Unit—what is it?

JAD: All Souls Unitarian Church.

ROBERT: Many times a month that church actually is host to a synagogue.

JAD: Oh my God, I hear them! Did you hear that? Like animals dying? Hey there!

JAD: So shofars were the horns that apparently knocked down the wall, so we wanted to measure how loud they could be, and we were lucky enough to find this guy.

DAVID PINCUS: Cantor Daniel Pincus.

JAD: Who got together about 10 people, everybody with their ram's horns.

DAVID PINCUS: Okay. This is a Yemenite shofar.

JAD: Though Daniel's was not quite a ram's horn.

DAVID PINCUS: Probably from either an animal called a kudu, perhaps. Or an antelope. I'm not exactly sure.

JAD: It's quite big!

DAVID PINCUS: Quite big. It's about two feet plus a few inches.

JAD: Wow.

DAVID PINCUS: In a somewhat corkscrew shape.

JAD: So in any case, he got us started. And we asked him to blow his shofar as loud as he could, and we were gonna measure the decibel level.

[Shofar blowing]

JAD: Just up to 96, but not quite there.

JAD: So that was our baseline: 96 decibels for one shofar player. But interestingly, when we doubled it and had two shofar players, listen to what happened.

[Shofars blowing]

JAD: That was 98.

JAD: We only got up to 98. Just shy of 99. And when we doubled that to four shofar players ...

[Shofars blowing]

JAD: We only bumped it up three more decibels.

JAD: Think we got 101.

[cheering and laughing]

JAD: Turns out—and this is actually a rule of thumb—anytime you want to bump up your overall volume by three decibels, you've gotta double the amount of shofar players. So if you want to go from 101 dB to 104, that means going from four shofar players to eight. If you want to go from 104 to 107, that means eight shofar players become 16. And if you want to go from there all the way up to our target ...

DAVID LUBMAN: 177 DB.

JAD: Well then you're gonna have to double yourself a lot!

ROBERT: So here's the question: how many in the end—how many shofars would you need to make the walls of Jericho come tumbling down?

DAVID LUBMAN: The number I calculated is 407,380.

ROBERT: [laughs]

JAD: What?

DAVID LUBMAN: And it might take awhile, too.

ROBERT: Well, wait a second. Seven is what the Bible says, and you just said 407,380.

DAVID LUBMAN: Yes.

JAD: That's five Rose Bowls full of trumpet players.

DAVID LUBMAN: Ah. But of course, if it was a miracle, all bets are off.

JAD: But what if you could get that number of people together, could you still do it? Can you knock down the wall?

DAVID LUBMAN: Well, with purely physics ...

ROBERT: According to David, we still have a problem, unfortunately.

DAVID LUBMAN: The problem I had was getting a very large number of men so close to the wall that we could produce the necessary pressure. And as I added men, I'd have to put them further and further back.

JAD: Imagine, he says, you've got all these hornblowers, hundreds of thousands, at this wall. You've got to organize them, put them in rows, and that creates a little bit of a situation.

DAVID LUBMAN: Ah, yes. Well, the people in the front row would have their heads blown off.

ROBERT: [laughs]

JAD: [laughs]

DAVID LUBMAN: By the blasts of the people behind them.

ROBERT: That's a sort of problem if you're a musician, I think.

DAVID LUBMAN: If you'd like, we could do an experiment. Do you volunteer?

ROBERT: No!

JAD: Okay, but what if you could put the people in the front row in helmets to protect them? Then could we do it?

ROBERT: Actually, we'd have another problem.

DAVID LUBMAN: That's right.

ROBERT: The sound, according to David, has to be focused. It has to actually sort of point ...

DAVID LUBMAN: ... at one spot on the wall.

ROBERT: When you put that many people together in front of a wall, some of them are gonna be way behind the ones in front.

JAD: Hmm. We're gonna lose focus.

WOODY NORRIS: And there's the problem.

ROBERT: But then we found Woody.

WOODY NORRIS: Yeah, my formal name is Elwood Norris. I go by Woody.

JAD: And we called Woody because well, he's an inventor.

WOODY NORRIS: President, chairman and CEO of a brand new company called Parametric Sound Corporation.

JAD: And he may be able to help us with our focus problem, because he's invented a technology that can beam sound in a direct line like a laser.

WOODY NORRIS: Which I'm going to demonstrate for your friend here.

KURT CONAN: Well, let's check some of these—some of these things out.

JAD: That's reporter Kurt Conan.

WOODY NORRIS: Okay, first I'm gonna play you this guy.

JAD: To demonstrate, he pulls out his sound beamer.

WOODY NORRIS: This is an ultrasonic emitter.

JAD: It's like a mini satellite dish, but kind of in a square.

WOODY NORRIS: Stand over there.

JAD: He and Kurt get on opposite sides of the room, very far apart, and then Woody shoots a concentrated beam of sound, in this case the sound of rushing water right at Kurt's head.

WOODY NORRIS: [laughs] Now if I shine it at you, see the difference? Just aim it at my chest. Almost a hundred percent gone.

KURT CONAN: Wow!

WOODY NORRIS: Magic.

ROBERT: Does your invention allow us to take the sound and put it into a beam such that it will hit a spot on the wall of Jericho?

WOODY NORRIS: Absolutely. With a caveat.

ROBERT: [laughs]

JAD: What's the caveat?

WOODY NORRIS: There is no known loudspeaker on the planet that can put out 170 decibels.

JAD: Really?

ROBERT: Oh.

WOODY NORRIS: My company makes some of the loudest speakers on the planet. They're known quite popularly around the world as an L-RAD—long-range acoustic device. They're sold to the military, police departments. And the loudest unit the company sells, which can be over $100,000 for one unit, puts out about 155 decibels.

ROBERT: That's not enough to knock down our wall, though.

WOODY NORRIS: No, not at all. There's another issue. This will be caveat number two.

JAD: Uh-oh.

WOODY NORRIS: When you get about 155-165 decibels, you get close to causing cavitation in the air where the air turns into a plasma.

ROBERT: [laughs]

JAD: What is ...?

ROBERT: You mean the sound won't travel through the air?

WOODY NORRIS: Only for a few millimeters.

JAD: We weren't able to a thousand percent confirm this, but according to Woody, even if we were able to make the necessary amount of noise, we would not be able to get that noise to the wall. The sound would just go ...

[Shofars blowing then fading]

ROBERT: We are just—there's an Anglo-Saxon word that would go right there, but we're talking about the Hebrews.

JAD: [laughs]

ROBERT: [laughs] Well, we are that thing and I don't know what to do.

DAVID LUBMAN: Well I had an alternate theory that could make the story plausible.

JAD: Ah!

DAVID LUBMAN: What I've imagined is that the attackers would try to undermine the wall by digging underneath it. And the defenders, figuring that the attackers would do that would send spies out to find out where the digging is so they can use countermeasures such as boiling oil.

ROBERT: [laughs] But—but, but ...

JAD: No, no. Wait, wait. Let him finish. I'm enjoying this.

DAVID LUBMAN: Okay. But then the attackers would say "They'll probably send out spies to find out where we're digging, so let's issue orders that nobody is to know where we are digging. And we won't tell those blabbermouth Israelites because it's sure to be picked up by one of the spies. And next thing you know, we'll have boiling oil on our head." In the meantime, the diggers, in order to keep the wall from falling in on them, they would prop it up with timbers. Then when the digging was about complete, they would pull out the whatever was the equivalent of a Zippo lighter in the Bronze Age, and light the timbers and then run like heck as the fire burned through. Eventually, that part of the wall would fall straight down.

ROBERT: No, you're rewriting the whole thing.

JAD: But where does the horn blowing come into the equation?

DAVID LUBMAN: Ah. Well, in the meantime, the spies report back, "We can't figure out where those Israelites are digging." So the King of Jericho probably says, "Well, we'll have to use the old hole-in-the-shield trick to find out." And so they take their Bronze Age shields with a hole in the middle, and they place them on the ground and put the ear to the hole. And they do this all around the perimeter of Jericho trying to hear the digging. But then the attackers say, "The defenders will probably use the old hole-in-the-shield trick. We know that. So we'll have to use acoustic warfare, make noise to prevent them from being able to hear where the digging is. So let's send out a bunch of priests with shofars to make noise."

ROBERT: [laughs] So your shofars are there to keep the shield-listening Jerichoans from overhearing the digging Hebrews. And the horns are just a way to mask the digging Hebrews's location.

DAVID LUBMAN: Yes.

ROBERT: This is very unsatisfactory.

JAD: Thanks to Daniel Lubman, Elwood "Woody" Norris, Daniel Pincus and his Shofar All-Stars.

RACHEL KELK: Rachel Kelk.

ANNA LEVY: Anna Levy.

ADAM HAMETZ-BERNER: Adam Hametz-Berner.

RICHARD SCHEINER: Richard Scheiner.

BOB WINE: Bob Wine.

ED KERSON: Ed Kerson.

DANIELA DRAKHLER: Daniela Drakhler.

MIRIAM FRANK: Miriam Frank.

JAD: I'm Jad Abumrad.

ROBERT: And I'm Robert Krulwich.

JAD: Bye!

[LISTENER: My name is Kayonne Wolf, and I'm a Radiolab listener in Hartford, Connecticut and an announcer for WNPR, Connecticut Public Radio. The Radiolab podcast is founded in part by the Sloan Foundation. Thanks. I hope that helps. You guys seriously made my whole month.]

[ANSWERING MACHINE: End of message.]

 

-30-

 

Copyright © 2024 New York Public Radio. All rights reserved. Visit our website terms of use at www.wnyc.org for further information.

 

New York Public Radio transcripts are created on a rush deadline, often by contractors. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of programming is the audio record.