Editing Sound reinforcement system (section)

===Power amplifiers===
[[Image:Poweramps.JPG|thumb|200px|Three audio power amplifiers]]
[[Image:Connectors of a QSC PLX2402 professional PA Power Amplifier.jpg|thumb|Rear panel of a power amplifier with 2 × 700 Watt (4 Ohm) - very similar to the topmost device in the image above - showing typical connectors for professional use: From left, symmetrical [[XLR connector|XLR]]-sockets for signal input, alternatively [[audio jack]] sockets, loudspeaker terminals of type [[Speakon]] (center), alternatively conventional [[screw terminal]]s for the loudspeaker cables (black and red per channel).]]

A [[power amplifier]] is an electronic device that uses electrical power and circuitry to boost a [[line level]] signal and provides enough electrical power to drive a loudspeaker and produce sound. All loudspeakers, including [[headphones]], require power amplification. Most professional audio power amplifiers also provide protection from [[clipping (audio)|clipping]] typically as some form of [[limiting]]. A power amplifier pushed into clipping can damage loudspeakers. Amplifiers also typically provide protection against [[short circuit]]s across the output and overheating.

Audio engineers select amplifiers that provide enough [[Headroom (audio signal processing)|headroom]]. Headroom refers to the amount by which the signal-handling capabilities of an audio system exceed a designated [[nominal level]].<ref>{{cite web |url=http://www.soundonsound.com/sound-advice/q-what-exactly-headroom-and-why-it-important |title=Q. What exactly is 'headroom' and why is it important? |date=February 2010 |publisher=[[Sound on Sound]]}}</ref> Headroom can be thought of as a safety zone allowing transient audio peaks to exceed the nominal level without damaging the system or the audio signal, e.g., via [[clipping (audio)|clipping]]. Standards bodies differ in their recommendations for nominal level and headroom. Selecting amplifiers with enough headroom helps to ensure that the signal will remain clean and undistorted.

Like most sound reinforcement equipment, professional power amplifiers are typically designed to be mounted within standard [[19-inch rack]]s. Rack-mounted amps are typically housed in [[road case]]s to prevent damage to the equipment during transportation. Active loudspeakers have internally mounted amplifiers that have been selected by the manufacturer to match the requirements of the loudspeaker. Some active loudspeakers also have equalization, crossover and mixing circuitry built in.

Since amplifiers can generate a significant amount of heat, thermal dissipation is an important factor for operators to consider when mounting amplifiers into equipment racks.<ref name="vasey1999concert">{{cite book |title=Concert Sound and Lighting Systems |last=Vasey |first=John |isbn=9780240803647 |lccn=lc99030654 |url=https://books.google.com/books?id=emthlAnw7l4C |date=1999 |publisher=Focal Press |chapter=5, Power amplifiers}}</ref>  Many power amplifiers feature internal fans to draw air across their heat sinks. The heat sinks can become clogged with dust, which can adversely affect the cooling capabilities of the amplifier.

In the 1970s and 1980s, most PAs employed heavy [[class AB amplifier]]s. In the late 1990s, power amplifiers in PA applications became lighter, smaller, more powerful, and more efficient, with the increasing use of [[switching power supplies]] and [[class D amplifier]]s, which offered significant weight- and space-savings as well as increased efficiency. Often installed in railroad stations, stadia, and airports, class D amplifiers can run with minimal additional cooling and with higher rack densities, compared to older amplifiers.

Digital loudspeaker management systems (DLMS) that combine digital crossover functions, compression, limiting, and other features in a single unit are used to process the mix from the mixing console and route it to the various amplifiers. Systems may include several loudspeakers, each with its own output optimized for a specific range of frequencies (i.e. bass, midrange, and treble).  [[Bi-amping and tri-amping]] of a sound reinforcement system with the aid of a DLMS results in more efficient use of amplifier power by sending each amplifier only the frequencies appropriate for its respective loudspeaker and eliminating losses associated with [[passive crossover]] circuits.