How Do Car Horns Work?

The next time you honk your car horn at that jerk who cut you off, you’ll understand how it uses physics to get the job done.

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Episode Transcript

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That's the Great Courses Plus dot com slash brain Stuff.
Welcome to brain Stuff from How Stuff Works. My name
is Christian, My world is fire and blood. Once I
hunked the horn of my interceptive Pursuit special, it's hard

(02:11):
to know who was more crazy, me or everyone else. No, really,
when people haunt car horns, they're pretty freaking aggressive. Research
shows were more likely to do it when it's hot outside,
when it's a week day, and if you're male, that's right.
War boys here in the US, your run of the
mill car horn is a hundred and ten decibels of

(02:32):
sustained noise. While the vehicle horns of yesteryear had different
combinations of notes, today they're mostly regulated to sound the same,
and the law requires you to have a car horn
if they're so important. Let's talk about how car horns work.
Typical car horns these days are electro mechanical. There are

(02:53):
two horns per vehicle, usually each sounding at a different
pitch to produce a cord. These horns generally consist of
a spring, steel diaphragm, a coiled wire, a switch, and
housing that amplifies sound like a megaphone. All of this
is mounted somewhere behind your vehicle's grill. So when you

(03:15):
slam your hand on that steering wheel button with a
little trumpet symbol on it, it sends an electrical current
through a relay and onto a copper coil that supplies
electricity to the horn. To create such a loud sound
takes a lot of energy. In fact, the only accessory
that uses more juice in your car is the starter.

(03:36):
The electrical current surging into the horn creates a magnetic field.
This field causes the flat circular diaphragm inside to oscillate.
The oscillation is set up by the diaphragm flexing to
its mechanical limit and then releasing back past its neutral position,
only to be pulled forward again. This functions by using

(03:58):
the basic law of elasticity, also known as Hook's law
because it was formulated in the seventeenth century by an
English scientist named Robert Hook. The law states that the
strain of a body is proportional to the stress applied
to the body. What this means for the car horn
is that it's diaphragm will oscillate continuously as long as

(04:19):
the current is applied. There are also other types of
horns used in vehicles, air horns, Clason's whistles similar to
organ pipes, and even sirens like we see on emergency vehicles,
but the electro magnetic car horn is the most common one.
You're going to find out there in the waste land.
Now that you're armed with this knowledge, you should be

(04:41):
ready to grab the sun and ride into Valhalla. Check
out the brain stuff channel on YouTube, and for more
on this and thousands of other topics, visit how stuff
works dot com.