Megafon
- För teleoperatören, se Megafon (företag).
En megafon är en portabel, ofta handhållen, trattformad apparat som är avsedd att förstärka eller rikta en persons röst. Till exempel används megafoner ofta vid sportevenemang, filminspelningar, demonstrationer eller för att styra större folkmassor.
Det finns även batteridrivna apparater bestående av en mikrofon, förstärkare och hornhögtalare sammanbyggda. Mikrofonen kan också vara kabelansluten.
Historik
Vem som var den ursprunglige uppfinnaren av megafonen är föremål för historiska kontroverser. Både Samuel Morland och Athanasius Kircher uppfann megafoner vid omkring samma tid under 1600-talet. Morland, beskrev i ett arbete publicerat 1655, sina experiment med olika horn. Hans största megafon bestod av en 6 meter lång koppartub och kunde, enligt uppgift, projicera en persons röst på två och en halv kilometers avstånd.[1]
Referenser
Noter
- ^ Mills, Mara. "When Mobile Communication Technologies Were New." Endeavour 33.4 (2009): 141-47.
Externa länkar
Wikimedia Commons har media som rör Megafon.
Media som används på denna webbplats
Författare/Upphovsman: Pedro Ribeiro Simões, Licens: CC BY 2.0
Protester during the pt:Geração à rasca rally, in 12 March 2011, at Avenida da Liberdade, Lisboa, Portugal.
Författare/Upphovsman: Chetvorno, Licens: CC0
Animation showing the operation of a reflex loudspeaker. Drawing shows a cross section through the speaker, the construction is cylindrically symmetrical. The reflex or reentrant loudspeaker, also called a megaphone, bullhorn, or loudhailer, is a type of folded horn speaker widely used in public address systems. It consists of a specialized diaphragm loudspeaker called a compression driver (a) attached to a metal or plastic horn (d). The driver has a small metal diaphragm (blue) driven to vibrate by the audio signal current flowing through a coil of wire (red) between the poles of a cylindrical magnet (green). The horn serves to couple the diaphragm more efficiently to the air, allowing it to radiate more of its energy as sound than a conventional horn speaker, making it louder. The horn sound path must be several feet long, so to make the speaker more compact the sound path is "folded" into a zigzag shape by several concentric exponentially-widening ducts. The sound waves pass forward through an inner tube (b) in the central projection in the horn, back through a larger concentric tube (c), then out through the surrounding horn (d).
Reentrant loudspeakers can be 10 times as efficient as cone loudspeakers, and so their output can be 10 dB louder when operating from the same amplifier. However their frequency response is very uneven and limited, with a bandwidth of 300-400 Hz to 5 kHz, so they have a distinctive "tinny" sound and are only used for the human voice.
(c) Bundesarchiv, Bild 183-H0729-0035-001 / Franke, Klaus / CC-BY-SA 3.0
![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/"Getting_em_up"_at_U.S.Naval_Training_Camp%2C_Seattle%2C_Washington._Webster_%26_Stevens._-_NARA_-_533698.tif/lossy-page1-125px-"Getting_em_up"_at_U.S.Naval_Training_Camp%2C_Seattle%2C_Washington._Webster_%26_Stevens._-_NARA_-_533698.tif.jpg)
- Scope and content: A sailor using a megaphone to increase the loudness of a bugle to wake recruits at U.S.Naval Training Camp, Seattle, Washington in 1947
- General notes: Use War and Conflict Number 455 when ordering a reproduction or requesting information about this image.
(c) Bundesarchiv, Bild 102-10044 / CC-BY-SA 3.0
The first major Reichswehr maneuvers this year in the region Munster in Hanover! Using a megaphone to impart instructions to Army units to cover artillery batteries.