Editing Loudspeaker (section)

====Horn loudspeakers====
{{Main|Horn loudspeaker}}
[[File:3-way horn speaker.png|thumb|A three-way loudspeaker that uses horns in front of each of the three drivers: a shallow horn for the tweeter, a long, straight horn for mid frequencies and a folded horn for the woofer]]
[[File:Klipschorn speaker drawing 1948 (cropped).png|Klipschorn speaker drawing, 1948|thumb]]

[[Horn loudspeaker]]s are the oldest form of loudspeaker system. The use of [[Horn (acoustic)|horns]] as voice-amplifying [[megaphone]]s dates at least to the 17th century,<ref>{{Cite EB1911|wstitle=Trumpet, Speaking and Hearing}}</ref> and horns were used in mechanical [[Phonograph|gramophones]] as early as 1877. Horn loudspeakers use a shaped [[waveguide]] in front of or behind the driver to increase the directivity of the loudspeaker and to transform a small diameter, high-pressure condition at the driver cone surface to a large diameter, low-pressure condition at the mouth of the horn. This improves the acoustic—electro/mechanical impedance match between the driver and ambient air, increasing efficiency, and focusing the sound over a narrower area.

The size of the throat, mouth, the length of the horn, as well as the area expansion rate along it must be carefully chosen to match the driver to properly provide this transforming function over a range of frequencies.{{efn|Every horn performs poorly outside its acoustic limits, at both high and low frequencies.}} The length and cross-sectional mouth area required to create a bass or sub-bass horn dictates a horn many feet long. ''Folded'' horns can reduce the total size, but compel designers to make compromises and accept increased cost and construction complications. Some horn designs not only fold the low-frequency horn but use the walls in a room corner as an extension of the horn mouth. In the late 1940s, horns whose mouths took up much of a room wall were not unknown among hi-fi fans. Room-sized installations became much less acceptable when two or more were required.

A horn-loaded speaker can have a [[Sensitivity (electroacoustics)|sensitivity]] as high as 110&nbsp;dB<sub>SPL</sub> at 2.83 volts (1 watt at 8 ohms) at 1 meter. This is a hundredfold increase in output compared to a speaker rated at 90&nbsp;dB sensitivity (given the aforementioned specifications) and is invaluable in applications where high sound levels are required or amplifier power is limited.