page_title: Horn loudspeaker
section_title: Technology history
hierarchical_section_title: Horn loudspeaker / Technology history
caption_attribution_description: English: Dog looking at and listening to a phonograph. Francis Barraud's 1898 painting of Nipper looking into an Edison Bell cylinder phonograph.
context_page_description: A horn loudspeaker is a loudspeaker or loudspeaker element which uses an acoustic horn to increase the overall efficiency of the driving element. A common form consists of a compression driver which produces sound waves with a small metal diaphragm vibrated by an electromagnet, attached to a horn, a flaring duct to conduct the sound waves to the open air. Another type is a woofer driver mounted in a loudspeaker enclosure which is divided by internal partitions to form a zigzag flaring duct which functions as a horn; this type is called a folded horn speaker. The horn serves to improve the coupling efficiency between the speaker driver and the air. The horn can be thought of as an "acoustic transformer" that provides impedance matching between the relatively dense diaphragm material and the less-dense air. The result is greater acoustic output power from a given driver.
  The narrow part of the horn next to the driver is called the "throat" and the large part farthest away from the driver is called the "mouth". The angular coverage of the horn is determined by the shape and flare of the mouth.
context_section_description: The physics (and mathematics) of horn operation were developed for many years, reaching considerable sophistication before WWII. The most well known early horn loudspeakers were those on mechanical phonographs, where the record moved a heavy metal needle that excited vibrations in a small metal diaphragm that acted as the driver for a horn. A famous example was the horn through which Nipper the RCA dog heard "His Master's Voice". The horn improves the loading and thus gets a better "coupling" of energy from the diaphragm into the air, and the pressure variations therefore get smaller as the volume expands and the sound travels up the horn.  This kind of mechanical impedance matching was absolutely necessary in the days of pre-electrical sound reproduction in order to achieve a usable sound level.
caption: Francis Barraud's original painting of Nipper looking into an Edison Bell cylinder phonograph.
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