I decided I would take this and scale it up to this

But I've never actually made something this big for my channel before so as usual we decided to make a smaller prototype

Model to see what we could learn about the challenges that would come from scaling it all the way up

So we started by creating a plaster mold with the right curvature

then you cover that with a gel coat and then we put three layers of fiberglass and

Polyester resin and then when you pop it out of the mold, you're left with this

We're immediately struck that there is in fact something really special about this shape

So I'm going to switch over from my lav mic to my shotgun mic for this demo

Here's my voice normal.

here's my voice while using the tube

which shows there's more going on here than just focusing the sound in one direction

Here's my voice using the horn

You can even hear me whisper... which is creepy

So this was proof that the curved shape of the horn had a significant effect on amplifying the input sound

But I still wasn't sure why, so now it's time to really scale things up to the big monster horn

Which we did by applying all the same principles

We learned on the prototype and then we headed to the most desolate location we could find on Google Maps to put it together

[Some cool music]

Mark's assistant: "Can you hear me"

Mark's assistant: "Hello over there!"

Mark: "It feels like you're like right on my shoulder"

As you know, the base of the horn is what's responsible for creating all the sound so to see what's inside

I thought it was only appropriate to open it with my friends Dan and Lincoln from the popular YouTube channel

What's Inside. And it turns out it's pretty simple: the key is this thin metal circular plate or diaphragm.

So the air comes in here at 100 psi and passes around this diaphragm in such a way that it causes it to vibrate

110 times in a second which causes a corresponding pressure wave to shoot out here and down the throat of the horn

So after a few hours, everything was finally set up and it was the moment of truth since after 8 months

None of us had actually ever heard it fire yet and Lincoln hadn't even seen the thing because we made him wait in the car

Mark: "This is the big reveal"

Mark: "You Ready?"

One two, here it is

[high pitched air horn]

Isn't that pretty loud?

Lincoln: "Wow, that's so cool!"

This actually isnt it, its that. The idea, now you can learn

[Lincoln:] Oh my!

Before we fire it

We need to first talk about how hearing works and what I eventually learned about why horns have that curved shape

Let's say this jello block represents a volume of air molecules if that horn diaphragm hits the jello molecules over here

There's a chain reaction of jello molecules crashing into each other

Until finally you see movement on the other side of the jello block and this is where your eardrum is

So it moves back and forth at the same rate as the horn diaphragm because of all of these

collisions of the jello

molecules in between

this is called a pressure wave and it's how sound travels through air and so if the horn diaphragm is hitting the air molecules at

A high frequency or very frequently our brain decodes that as a high pitch

But if the crashes are happening at a low frequency or less frequently than our brain decodes that as a low pitch. Okay

But why the curvy horn shape? Well that has to do with something called impedance matching

Basically, the horn diaphragm is very solid and strong and it pushes against the air which doesn't offer much resistance

It's not very effective like trying to break a piece of paper by punching it

So without the curvy horn portion as the diaphragm moves back and forth

It interfaces with the air sort of like this. You can still see the jello is moving on the opposite side

Just not that much because the air is just too thin and weak over this small of an area

So to have a better interface with the air you put a big curvy shape right after the diaphragm

You can see now your eardrum is moving back and forth much more vigorously because the interface is so much better

so the sounds louder with a curved horn not because you're amplifying the sound but because you're conserving the sound this makes sense because

Amplifying means you're adding power to the system and there's no battery or plugs at the curve section of a horn

It's passive

So by impedance matching you give yourself a much larger area to push against all the air at the outlet which makes for a more

effective chain reaction of molecules crashing into your eardrum

And now the horn

Isn't that pretty loud?

Lincoln: "Wow, that's so cool!"

Is that pretty good?

This actually isnt it, its that. The idea, now you can learn

[LOUD Horn sound]

[LOUD Horn sound]

[laughter]

Oh my gosh

Just like eight months of work

That's the first time we've actually fired off and that's behind the horn

Dan: I could feel the vibrations

Yeah

[?] be in front of that thing

We're gonna go see what it's like on the other side. All right

So this is we're about two football fields away from the horn. We have no idea how loud this is gonna sound here

All right Ken, fire the normal air horn

(Air horn firing)

Yeah, we could hear it now we're a little nervous cuz you can hear it decently well

Alright, firing

[BIG horn firing]

[laughs]

So for our second test we drove about a mile(1.6 Km) away and you can barely see the horn right here

Alright, Ken fire.

[Air horn firing]

Lincoln: We can still completley hear it, that's crazy

You can hardly see that massive horn, but it's still super loud. So let's just drive keep going

We're gonna go real far

So from satellite view

This is where the horn was

Here was the first spot and then the second spot and then here was the third spot two and a half miles[4 Km] away

Okay, so the horn is now super far away. I literally can't see with my naked eye.

Dan: It's so far away

Dan: I can barely see it. It's right at the crest of the hill. There's a little tiny speck and it's right there

We're gonna do an experiment and we're gonna test the speed of sound

We should hear it on this walkie-talkie and then some amount of time later

We might be able to hear it from this distance

Lincoln's gonna measure the time on his stopwatch and then we should be able to calculate from there what the speed of sound is

We're ready when you ar

bwowwwwwwwwwww

[temporary silence ]

Mark:Wait for it

Vmmmmmmmm

That's crazy! How long. It took 11 seconds

for the sound of the horn to get here

It's so clear. Like I feel like we can go 10 miles further

Think about what this means?

It took an unbroken chain of two and a half miles of air molecules 11 seconds to all collide with each other

Until they made it all the way down here and bumped into the air molecules in our ear canals which then bumped into our eardrums

Hi!

Wait, what if I scream?

[Screams]

So the Sun was quickly going down

But before we went home

We wanted to try and break some glass and if you want to break glass with what is essentially little puffs of air the trick

Is to find out its resonant frequency. You actually know all about this

If you've ever used one of these I can make Eliza go really high

With just a little force now if I apply that force at random intervals, it doesn't do very much. It's not fun, huh?

No, it's not fun

But if I apply that force equal to the timing of the natural frequency of the swing those little pushes add to each other

Go higher Mark Rober

And so in this case the resonant frequency increased our fun, but if engineers don't take this into consideration

It could lead to disaster such as when wind gusts going at just the right rate destroy the Tacoma Narrows Bridge

It's also why soldiers don't march in unison when crossing a bridge

So if you measure the natural frequency of the glass with an accelerometer like this

Then you just need to make sure your horn fires at that exact frequency or a multiple there of

Or you can just change the natural frequency of the glass to match your horn by adding weights in the right spot

[Glass break]

Shoutout to Lincoln and Dan from What's Inside for helping me out. We actually investigated

What's inside an old Japanese air-raid siren for their video?

It's a totally different way to make a really loud sound

So you should go check that out using the link in the description

This horn is easily the largest thing I've ever built for my channel and it took eight months of coordination with my former NASA

buddy Ken to pull it off

The problem is that Ken lives way down here by NASA but I live 400 miles up this way

So I partnered with Portal from Facebook to better collaborate on the design and build process

So he put a portal in his workshop and I set up a portal plus in mine and besides the high fidelity audio

And the HD video. I think the coolest thing about portal is the smart camera feature, which you see in action here

So as I would move around my workshop and Ken moved around his the camera frames the video to keep us both centered and this

Is great for us because we're not

constantly moving the cameras around or tied to just working in one spot and smart sound enhances our voices as we move about so we

Can still hear each other regardless of other shop noise

[Diaphragm drop off]

[Laugh]

And of course when it comes to any device in a home, privacy is a big deal

So with a single tap portal will allow you to disconnect both the camera and the microphone or if you prefer an analog solution

They provide a camera cover

Also, the smart camera uses AI technology that runs locally on portal not on some remote servers.

At the end of the day, it's a great piece of hardware and it worked really well for us

So if you want to learn more about Portal or maybe even get your own just go ahead and use the link in the video description.

Thanks for watching

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