What Are the Physics of a Megaphone?

physics-megaphone Credit: Gareth Davies/CC-BY-2.0

A megaphone directs or funnels the voice to a specific direction, and it also regulates the distribution of sound waves from the mouth to the open medium. The secret behind the workings of a megaphone is in its shape.

Usually handheld and cone shaped, a megaphone is a portable device that amplifies the voice coming from a person's mouth and targets the sound to a specific destination. The most common design of a megaphone is cone shaped, wherein a person speaks through the narrow end of the megaphone, and the sound is emitted at the wider end.

The science behind the megaphone involves two concepts. First, a megaphone is designed to channel sound waves to a particular direction. When a person speaks normally, the sound waves from his voice emanate from the vocal cords to the open air. In this scenario, the sound waves scatter in all directions, thereby reducing the amount of sound that the receiving person hears. In contrast the megaphone directs the voice sound waves to the direction where the wide end is pointed, thereby resulting in more sound waves reaching the listener.

The second concept involves the design of a megaphone, which boosts the acoustic impedance of a person's vocal cords, resulting in stronger vocal power. The vastness of the open air causes a backward reflection of a talker's vocal sound waves, resulting in a reduction of sound power. With the megaphone's conical shape, the narrow opening of the mouth is gradually opened by the wider end of the megaphone, thereby reducing the effect of wave reflection and increasing the sound volume to the receiver.