A megaphone, speaking trumpet, bullhorn, blowhorn, or loudhailer is usually a portable or hand-held, cone-shaped acoustic horn used to amplify a person's voice or other sounds and direct it in a given direction. The sound is introduced into the narrow end of the megaphone, by holding it up to the face and speaking into it, and the sound waves radiate out the wide end. A megaphone increases the volume of sound by increasing the acoustic impedance seen by the vocal cords, matching the impedance of the vocal cords to the air, so that more sound power is radiated. It also serves to direct the sound waves in the direction the horn is pointing. It somewhat distorts the sound of the voice because the frequency response of the megaphone is greater at higher sound frequencies. Since the 1960s the voice-powered acoustic megaphone described above has been replaced by the electric megaphone, which uses a microphone, an electrically-powered amplifier and a folded horn loudspeaker to amplify the voice.
History Before it became a megaphone, the bull horn or cow horn or steer horn was a signaling device or bugle used from antiquity. The initial inventor of the speaking trumpet is a subject of historical controversy. There have been references to speakers in Ancient Greece (5th Century B.C.) wearing masks with cones protruding from the mouth in order to amplify their voices in theatres. Hellenic architects may have also consciously utilized acoustic physics in their design of theatre amphitheaters. A drawing by Louis Nicolas (see image) on page 14 of the Codex canadensis, circa 1675 to 1682, shows a Native American chief named Iscouakité using a megaphone made of birch bark. The text of the illustration says that he is addressing his soldiers through a birch bark tube. Both Samuel Morland and Athanasius Kircher have been credited with inventing megaphones around the same time in the 17th century. Morland, in a work published in 1672, wrote about his experimentation with different horns. His largest megaphone consisted of over 6 m (20 ft) of copper tube and could reportedly project a person's voice a mile and a half. More than twenty years earlier, Kircher had described a device that could be used as both a megaphone and for "overhearing" people speaking outside a house. His coiled horn would be mounted into the side of a building, with a narrow end inside that could be either spoken into or listened to, and the wide mouth projecting through the outside wall. Morland favored a straight, tube-shaped speaking device. Kircher's horn, on the other hand, utilized a "cochleate" design, where the horn was twisted and coiled to make it more compact. A later, papier-mâché trumpet of special design was the Sengerphone. Additionally, in ruins of Tiwanaku are stones around the central place with holes shaped in a megaphone's profile. Their purpose is today unknown, but as local guards can show, it is possible to amplify a human voice loud enough to hear it across a large area. The term 'megaphone' was first associated with Thomas Edison's instrument 200 years later. In 1878, Edison developed a device similar to the speaking trumpet in hopes of benefiting the deaf and hard of hearing. His variation included three separate funnels lined up in a row. The two outer funnels, which were 2,030 mm long, were made of paper and connected to a tube inserted in each ear. The middle funnel was similar to Morland's speaking trumpet, but had a larger slot to insert a user's mouth. With Edison's megaphone, a low whisper could be heard a 300 m away, while a normal tone of voice could be heard roughly 3 km away. On the listening end, the receiver could hear a low whisper at 300 m. However the apparatus was much too large to be portable, limiting its use. George Prescott wrote: "The principal drawback at present is the large size of the apparatus." Prior to the invention of the electric microphone, some early pop singers, such as Rudy Vallée, sang with a megaphone as their quieter voices, the hallmark of a "crooner", were often not loud enough for live performances. Since the 1960s, acoustic megaphones have generally been replaced by electric versions (below), although the cheap, light, rugged acoustic megaphone is still used in a few venues, like cheering at sporting events and cheerleading, and by lifeguards at pools and beaches where the moisture could damage the electronics of electric megaphones.
Electric megaphone
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