Editing Loudspeaker (section)

===Enclosures===
{{Main|Loudspeaker enclosure}}
[[File:4-Wege Lautsprecher.jpg|thumb|upright|An unusual three-way speaker system. The cabinet is narrow to raise the frequency where a diffraction effect called the ''baffle step'' occurs]]

Most loudspeaker systems consist of drivers mounted in an enclosure, or cabinet. The role of the enclosure is to prevent sound waves emanating from the back of a driver from interfering destructively with those from the front.  The sound waves emitted from the back are 180° [[out of phase]] with those emitted forward, so without an enclosure they typically cause cancellations which significantly degrade the level and quality of sound at low frequencies.

The simplest driver mount is a flat panel (''baffle'') with the drivers mounted in holes in it. However, in this approach, sound frequencies with a wavelength longer than the baffle dimensions are canceled out because the antiphase radiation from the rear of the cone interferes with the radiation from the front. With an infinitely large panel, this interference could be entirely prevented. A sufficiently large sealed box can approach this behavior.<ref>{{cite web |url=http://www.soundonsound.com/sos/jun04/articles/qa0604-6.htm |publisher=Sound on Sound |date=June 2004 |title=Q. What's the Difference between Ported and Un-Ported Monitors? }}</ref><ref>{{cite web |url=http://www.record-producer.com/learn.cfm?a=97 |publisher=Record Producer |title=Infinite Baffle |archive-url=https://web.archive.org/web/20051112115053/http://www.record-producer.com/learn.cfm?a=97 |archive-date=November 12, 2005 }}</ref>

Since panels of infinite dimensions are impossible, most enclosures function by containing the rear radiation from the moving diaphragm. A sealed enclosure prevents transmission of the sound emitted from the rear of the loudspeaker by confining the sound in a rigid and airtight box. Techniques used to reduce the transmission of sound through the walls of the cabinet include thicker cabinet walls, internal bracing and lossy wall material.

However, a rigid enclosure reflects sound internally, which can then be transmitted back through the loudspeaker diaphragm—again resulting in degradation of sound quality. This can be reduced by internal absorption using absorptive materials such as [[glass wool]], wool, or synthetic fiber batting, within the enclosure. The internal shape of the enclosure can also be designed to reduce this by reflecting sounds away from the loudspeaker diaphragm, where they may then be absorbed.

Other enclosure types alter the rear sound radiation so it can add constructively to the output from the front of the cone. Designs that do this (including ''[[bass reflex]]'', ''passive radiator'', ''transmission line'', etc.) are often used to extend the effective low-frequency response and increase the low-frequency output of the driver.

To make the transition between drivers as seamless as possible, system designers have attempted to time align the drivers by moving one or more driver mounting locations forward or back so that the acoustic center of each driver is in the same vertical plane. This may also involve tilting the driver back, providing a separate enclosure mounting for each driver, or using electronic techniques to achieve the same effect. These attempts have resulted in some unusual cabinet designs.

The speaker mounting scheme (including cabinets) can also cause diffraction, resulting in peaks and dips in the frequency response. The problem is usually greatest at higher frequencies, where wavelengths are similar to, or smaller than, cabinet dimensions.
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====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.

==== Transmission line loudspeaker ====
{{Main|Transmission line loudspeaker}}

A [[transmission line loudspeaker]] is a loudspeaker enclosure design that uses an [[acoustic transmission line]] within the cabinet, compared to the simpler enclosure-based designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long (generally folded) damped pathway within the speaker enclosure, which allows greater control and efficient use of speaker energy.
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