Editing Sound reinforcement system (section)

===Main loudspeakers===
[[File:Line Array and Subs.jpg|thumb|left|250px|A large line array with separate subs and a smaller side fill line array.]]
A simple and inexpensive PA [[loudspeaker]] may have a single full-range [[loudspeaker driver]], housed in a suitable enclosure. More elaborate, professional-caliber sound reinforcement loudspeakers may incorporate separate drivers to produce low, middle, and high [[frequency]] sounds. A [[crossover network]] routes the different frequencies to the appropriate drivers. In the 1960s, [[Horn loudspeaker|horn loaded]] theater and PA speakers were commonly columns of multiple drivers mounted in a vertical line within a tall enclosure.

The 1970s to early 1980s was a period of innovation in loudspeaker design with many sound reinforcement companies designing their own speakers using commercially available drivers. The areas of innovation were in cabinet design, durability, ease of packing and transport, and ease of setup. This period also saw the introduction of the hanging or ''flying'' of main loudspeakers at large concerts. During the 1980s the large speaker manufacturers started producing standard products using the innovations of the 1970s. These were mostly smaller two way systems with 12", 15" or double 15" woofers and a [[Compression driver|high frequency driver]] attached to a high frequency horn. The 1980s also saw the start of loudspeaker companies focused on the sound reinforcement market.

The 1990s saw the introduction of [[line array]]s, where long vertical arrays of loudspeakers in smaller cabinets are used to increase efficiency and provide even dispersion and frequency response. [[Trapezoidal]]-shaped enclosures became popular as this shape allowed many of them to be easily arrayed together. This period also saw the introduction of inexpensive molded plastic speaker enclosures mounted on tripod stands. Many feature built-in power amplifiers which made them practical for non-professionals to set up and operate successfully. The sound quality available from these simple [[powered speakers]] varies widely depending on the implementation.

Many sound reinforcement loudspeaker systems incorporate protection circuitry to prevent damage from excessive power or operator error.  [[Resettable fuse]]s, specialized current-limiting light bulbs, and [[circuit breaker]]s were used alone or in combination to reduce driver failures. During the same period, the professional sound reinforcement industry made the Neutrik [[Speakon]] NL4 and NL8 connectors the standard speaker connectors, replacing [[1/4" jack]]s, [[XLR connector]]s, and [[Cannon (ITT Corporation)|Cannon]] multipin connectors which are all limited to a maximum of 15 amps of current. XLR connectors are still the standard input connector on active loudspeaker cabinets.

To help users avoid overpowering them, loudspeakers have a power rating (in [[watt]]s) which indicates their maximum power capacity. Thanks to the efforts of the [[Audio Engineering Society]] (AES) and the loudspeaker industry group ALMA in developing the EIA-426 testing standard, power-handling specifications became more trustworthy.

[[File:Mackie SWA1801 subwoofer.jpg|thumb|right|200px|An 18" Mackie [[subwoofer]] cabinet.]]
Lightweight, portable speaker systems for small venues route the low-frequency parts of the music (electric bass, bass drum, etc.) to a powered [[subwoofer]]. Routing the low-frequency energy to a separate amplifier and subwoofer can substantially improve the bass response of the system. Also, clarity may be enhanced because low-frequency sounds can cause [[intermodulation]] and other distortion in speaker systems.

Professional sound reinforcement speaker systems often include dedicated hardware for safely ''flying'' them above the stage area, to provide more even sound coverage and to maximize sightlines within performance venues.