A megaphone, speaking-trumpet, bullhorn, blowhorn, or loud hailer is a portable, usually hand-held, cone-shaped horn

Blowing horn

The blowing horn or winding horn is a sound device by and large shaped like a horn or actually a cattle or other animal horn arranged to blow from a hole in the pointed end of it...

 used to amplify a person’s voice or other sounds towards a targeted direction. This is accomplished by channelling the sound through the megaphone, which also serves to match the acoustic impedance

Acoustic impedance

The acoustic impedance at a particular frequency indicates how much sound pressure is generated by a given air vibration at that frequency. The acoustic impedance Z is frequency dependent and is very useful, for example, for describing the behaviour of musical wind instruments...

 of the voice cords to the air. The natural human voice

Human voice

The human voice consists of sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc. Its frequency ranges from about 60 to 7000 Hz. The human voice is specifically that part of human sound production in which the vocal folds are the primary...

 tends to spread evenly in all directions, whereas when it is sent through a megaphone, the sound is concentrated in a given direction and the coupling of its energy to the air optimised, while if a listener is to the side, it is more difficult to hear what is being said.

History

Though some instrument of the kind appears to have been in earlier use, the origin of the megaphone, or speaking trumpet as it was called, is connected with the name of Athanasius Kircher

Athanasius Kircher

Athanasius Kircher was a 17th century German Jesuit scholar who published around 40 works, most notably in the fields of oriental studies, geology, and medicine...

 and that of Sir Samuel Morland

Samuel Morland

Sir Samuel Morland, 1st Baronet , or Moreland, was a notable English academic, diplomat, spy, inventor and mathematician of the 17th century, a polymath credited with early developments in relation to computing, hydraulics and steam power.-Education:The son of Thomas Morland, the rector of...

, who in 1670 proposed to the Royal Society

Royal Society

The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...

 of London the question of the best form for a speaking trumpet. Johann Heinrich Lambert

Johann Heinrich Lambert

Johann Heinrich Lambert was a Swiss mathematician, physicist, philosopher and astronomer.Asteroid 187 Lamberta was named in his honour.-Biography:...

, in the Berlin Memoirs for 1763, seems to have been the first to give a theory of the action of this instrument, based on an altogether imaginary analogy with the behaviour of light.

A later, papier-mache

Papier-mâché

Papier-mâché , alternatively, paper-mache, is a composite material consisting of paper pieces or pulp, sometimes reinforced with textiles, bound with an adhesive, such as glue, starch, or wallpaper paste....

 trumpet of special design was the Sengerphone.

The first such device with the name Megaphone was an invention of Thomas Edison

Thomas Edison

Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...

.

Electric megaphones

In 1954, TOA Corporation developed the EM-202, the world's first electric megaphone.

An electronic megaphone amplifies sound to a higher decibel

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

 level. It can be amplified from over 90 dB. It consists of a microphone

Microphone

A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

, an amplifier

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

 and a loudspeaker

Loudspeaker

A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

. Common uses for megaphones are at sporting events, political functions, and generally when one needs to address congregations of people in open spaces.

External links

• Controlling Public Protest: First Amendment Implications An article about restrictions that may legally be imposed on public protests (including use of bullhorns), by Daniel L. Schofield, S.J.D., published in the November 1994 issue of the FBI
  Federal Bureau of Investigation
  The Federal Bureau of Investigation is an agency of the United States Department of Justice that serves as both a federal criminal investigative body and an internal intelligence agency . The FBI has investigative jurisdiction over violations of more than 200 categories of federal crime...
  
  's Law Enforcement Bulletin
  FBI Law Enforcement Bulletin
  The FBI Law Enforcement Bulletin is published monthly by the FBI Law Enforcement Communication Unit, with articles of interest to state and local law enforcement personnel...
  
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