The Complete Handbook of Bullhorns

Chapter 1: Understanding Bullhorns

A bullhorn, also known as a megaphone or loudhailer, is a self-contained public address system that amplifies a human voice using a powered transducer and a flared acoustic horn. The name "bullhorn" comes from the shape of the flared output that resembles the horn of a bull, and the term has stuck in North America, while "megaphone" is more common in Europe. In this handbook, we use "bullhorn" as a broad category name, covering everything from a 2-watt pocket unit to a 50-watt vehicle-mounted electronic siren.

The defining feature of a bullhorn, as opposed to a general-purpose powered speaker, is its integrated flared horn. That flare does two jobs: it matches the acoustic impedance of the driver to the open air, and it projects the sound in a directional beam. Acoustic impedance is a measure of how much resistance a medium (like air) offers to the propagation of sound waves. When a small speaker diaphragm (a few square centimeters) pushes against the air, most of its energy gets reflected back into the speaker, which is why a raw speaker is inefficient at converting electrical power into audible sound. The flared horn acts as a transformer: it provides a gradual transition from the high-pressure, low-displacement environment at the driver to the low-pressure, high-displacement environment at the open air. This is the same principle behind a trombone, a trumpet, and an organ pipe, but the bullhorn's flare is designed specifically for the frequencies of the human voice, roughly