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See? And NPR. Hello, I'm Jen. I'm Robert.
This is Radio Lab, the podcast. So today, a slightly offbeat exploration of acoustic warfare. We're going to do it by looking at the famous... You know the story?
I know what we're doing. Should I remind you of the story? I've heard the phrase walls of Jericho and I know nothing else about it. It's most famous as a song, Joshua, for the Battle of Jericho, Jericho, Joshua, for the Battle of Jericho, and the walls came tumbling down.
No idea. No idea. You don't know that? No.
Performing my time. Really? No, no, no, no. It's an ego spiritual.
It's a black American spiritual. It's like that. That's the only one. That's the only one.
Anyway. So tell us the story so we can get started. Well, as you know, the Hebrew people crossed the Red Sea and then wandered around in the desert for a while. We'll just say I do that.
40 years. And now we're up to, we're almost into the Promised Land, but there is this city called Jericho. Who's inside Jericho? Well, the Jericho.
Really? The Jericho. They don't know much about them, actually. No, they're just, they just, I think they have all these 40,000 people shut up and say, hey, who are these people?
I get them out of here. So they were just looking after their property? I suppose, or maybe they just didn't like what they saw. Okay.
Now Jericho. You're reading now. I'm reading from the Battle. Okay.
Now Jericho was tightly shut because of the sons of Israel. So I guess it got to take Jericho. Maybe that was it. I'm a little fuzzy here on the cause of the thing.
It had to be done. It had to be done. However, now quoting the Bible, Jericho was tightly shut because it had a wall. Yeah.
So read the part about how they knocked down the wall. Here's the formula. From the mouth of God. And they do this with seven trumpets, you say.
Yes. All right. So here we go. The question we have then for this podcast is what would it really take?
To do this. I'm talking without God. Only puny physics. You're your headphones.
Independent left. I'm not sure. I'm not sure. I'm not sure.
I'm not sure. I'm not sure. I'm not sure. I'm not sure.
I'm not sure. I'm not sure. I'm not sure. I'm not sure.
I'm not sure. I'm not sure. I'm not sure. Independent left and right.
One control should be fairly comfortable. Is it just in principle possible for sound to blow down a wall? That's their question. We actually called up a guy who thought about this.
I'm an acoustical consultant. David Lubman. His name. And an acoustical scientist.
And if you think about the nature of sound, it's a fluctuating pressure. Explain that when sound hits an object, the waves actually push the object but also pull at it. Many times per second. In theoretically he says, if you can get enough of those pushes and pulls on the wall.
Eventually it'll be in the crumble. So the first question he asked, naturally, is what kind of wall are we dealing with? Well, looking at the construction of Bronze Age walls in the Middle East, there were mud brick walls. The question then was how much sound would be necessary for volume to topple a wall like that?
Yeah. And he came up with a number. This is a technical number for the strength of the sound. You'd need to produce 177 dB.
177 dB. Yes. That would knock down the wall? Yes.
How many dBals just for scale is my voice right now, roughly? Your voice is probably about 60 or 65 dBals. Oh. So where are you a third of the way there, just talking?
Well, no. Joshua Jericho. Here's where the issues start. Turns out he says, it doesn't add up the way that you would think.
And there's a rub. Assume that your voice level is 60 dBals. In order to get 70 dBals, you would have to produce 10 times as much power. This didn't make much sense to us.
Until we ended up doing what he did and recruiting. Some experienced shofar blowers from synagogues. Yes. We went up to all souls unitarians church.
Many times a month that church actually has to a synagogue. Oh my God. I hear them. Did you hear that?
Like animals dying. Right there. So so far as 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.
Hunter. Daniel. Pinchas. Who got together about 10 people, everybody with their ram sorns.
Okay. This is a young night. So far. Daniel's was not quite a ram sorn.
Probably from either an animal called a kudu. Perhaps we went antelope. I'm not exactly sure. It's quite big.
It's about two feet plus a few inches in a somewhat corkscrew shape. So in case he got us started, we asked him to blow his shofar as loud as he could and we were going to measure the decibel level. So that was our baseline. 96 decibels for one shofar player.
But interestingly, we doubled it. Had two shofar players. Listen to what happened. We only got up to 98.
Just shy in 99. And when we doubled that, went from two to four shofar players, we only bumped it up three more decibels. Turns out, and this is actually a rule of thumb. Anytime you want to bump up your overall volume by three decibels, you've got to 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. 177 dB.
Well then you're going to have to double yourself a lot. But here's the question. How many in the end? How many shofars would you need to make the walls of shofar?
The number I calculated is 407,380. What? And it might take a while too. Well, ladies, I get seven is what the Bible says, and you just said 407,380.
Yes, and that would be a minimum number. That's five rose bowls full of trumpet blades. But of course, if it was a miracle, all bets are off. But what if you could get that number of people together?
Could you still do it? Could you not go on the wall? Well, with the puny physics. One today, but we still have a problem.
Unfortunately. 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. Imagine he says you've got all these horn blowers, 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. Oh, yes. Well, the people in the front row would have their heads blown off by the glass of the people behind him. That's a sort of problem if you're a musician.
If you'd like, we could do an experiment, do you volunteer? No. Okay, but what if you could put the people in the front row in helmets to protect them? Then you'd actually give another problem?
That's right. The sound, according to David, has to be focused. It has to actually sort of point at one spot on the wall. When you put that many people together in front of a wall, some of them are going to be way behind the ones in front.
We're going to lose focus. And there's the problem. Let me find Woody. Yeah, my formal name is Elwood Norris.
I go by Woody. We called Woody because, well, he's an inventor. President, chairman, and CEO of a brand-new company called Parametric Sound Corporation. 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.
Which I'm going to demonstrate for your friend here. Let's check some of these things out. That's reporter Kirk Conan. Okay, first I'm going to play you with this guy.
To demonstrate, he pulls out his sound beener. This is an old show of beener. It's like a mini satellite dish, but kind of in a swear. Instead of it.
He and Kirk 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?
It hurts head. No, if I shine it at you. The difference is that I just aim it at my chest. Almost 100% on.
Wow. Magic. 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? Absolutely with a caveat.
What's the caveat? There is no known loudspeaker on the planet that can put out 170 decibels. Really? 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.
Wow. Puts out about 155 decibels. That's not enough to knock down our wall though. No, not at all.
There's another issue. This will be a caveat number two. When you get about 155, 165 decibels, you get close to causing cavitation in the air where the air turns into a plasma. What does it mean the sound won't travel through the air?
Only for a few millimeters. We weren't able to 1000% 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... There we are just...
There's an Anglo-Saxon where it didn't go right there, but we're talking about Hebrews. But we are that thing. And I don't know what to do. Well, I had an alternate theory that could make the story plausible.
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. But... 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 should be picked up by one of the spies. And next thing you know, we'll have boiling oil in 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 whatever was the equivalent of a zippo lighter in the bronze age. And alight the timbers, and then run like heck. As the fire burned through, eventually that part of the wall would fall straight down. No, you're rewriting the whole thing?
But where does the horn going to go? 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-aid 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 Chofars to make noise.
Sorry, your Chofars are there to keep the shield listening Jerichoans from overhearing the digging Hebrews. And the ruins are just a way to mask the digging Hebrews' location. Yes, this is very unsatisfactory. Thanks to Daniel Looman, Elwoody Norris, Daniel Pinkis, and his Chofar All-Stars.
Nigel Cow, Adam, Adam, John, Adam, Richard, China, Bob, Wine, Ed, Kerson. Daniel, Jack, Perk. Miriam, Frank. I'm Jada Boomerad.
Hi, Robert Colitz. Bye. This is Ben P.R., Connecticut Public Radio. The radio lab podcast is founded in part by the Sloan Foundation.
Thanks, I hope that helps with you guys' seriously name a whole month. And this message.