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why do horns and musical instruments
have this flared shape to answer this
question about a year ago
i decided i would take this and scale it
up to this
and 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
with the tube to show that there's more
going on here than just focusing the
sound in one direction
and then here's my voice using the horn
you can even hear me whisper
which is creepy
so this was proof that the curve 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
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[Applause]
could you hear me hello
over there 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 danny 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 eight 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
this is the big reveal you ready yeah
one two here it is is that pretty loud
wow that's so cool is that pretty good
this actually isn't hard it's that
oh behind you now you can look oh my god
but 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 then 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
jellos 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 inner face is so much better
so it sounds louder with the 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
curved 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
is that pretty loud wow that's so cool
is that pretty good
this actually isn't hard it's that
behind you now you can look
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oh my
gosh this is like eight months of
work that's the first time we've
actually fired off
and that's behind the horn i could feel
the vibrations
yeah not even in front of the 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
yeah we could hear it now we're a little
nervous because you can hear it decently
well
all right firing
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so for our second test we drove about a
mile away and you can barely
see the horn right here all right ken
fire
now
i mean you can hardly see that massive
horn but it's still super loud so let's
just
drive keep going all right we're gonna
go real far so from a 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 away
okay so the horn is now super far away i
literally can't see it with my naked eye
it's so far away like 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 or 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 are okay i'm ready
wait for it
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that's crazy how long it took 11 seconds
for the sound of the horn to get here
we can still hear it so clearly 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
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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 elisa 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
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 destroyed 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 thereof
or you can just change the natural
frequency of the glass to match your
horn by adding weights in the right spot
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[Applause]
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you're so fun