Science Behind The Sound: What Makes an Electric Horn Beep?

Ever been sitting in traffic wondering just how the horn blaring in your ear works? Well look no further.

In order to produce sound, electric horns go through a two step cycle hundreds of times per second while the horn is activated. Figure 1, below, is a cross sectional view intended to help with the visualization of this process within an electro-mechanical horn (solid state electric horns are only slightly different. Today, we outline the science behind the sound of an electro-mechanical horn broken down into two easy to follow steps.

STEP 1:

The horn on the left shows the resting position of the internal components when it is not connected to power. Once it is supplied with a current, the coil will create a magnetic field which then polarizes the plunger and pole piece causing them to become attracted to each other. Because the pole piece is firmly mounted to the casing of the horn, the plunger and the diaphragm will be pulled inward towards it.

Information on the cycle of electric horns was found in this patent: https://patents.google.com/patent/US4813123

STEP 2:

When the plunger is pulled in, it will cause the contacts to break the circuit, which is shown on the right side of figure 1. This means there is no longer a magnetic field being produced by the coil, and the plunger will be pulled by the diaphragm back to the initial resting position. Now the contacts will reconnect causing the cycle to continue with a frequency of 300-500 Hz until connection to the power supply is terminated. So basically, all electric horns are just electro-magnets being turned on and off really fast in order to vibrate the diaphragm and make sound waves!

FUNCTIONS OF OTHER PARTS

The bracket, which is not shown in the diagram, attaches the horn to the vehicle and plays a role in the production of sound by vibrating with the diaphragm and plunger. The purpose of the tuning screw is to allow the manufacturer of the horn to adjust the distance the plunger travels during the cycle by changing how close the contacts are. This ensures that resonance is reached, therefore producing the loudest sound possible for the amount of power the horn receives.