Origins of Sound Systems
The sound system concept first became popular in the 1950s, in the ghettos of Kingston. DJs would load up a truck with a generator, turntables, and huge speakers and set up street parties. In the beginning, the DJs played American rhythm and blues music, but as time progressed and more local music was created, the sound migrated to a local flavor. The sound systems were big business, and represented one of the few sure ways to make money in the unstable economy of the area. The promoter (the DJ) would make his profit by charging a minimal admission, and selling food and alcohol. It was not uncommon for thousands of people to be in attendance. By the mid 1950s, sound systems had eclipsed live musicians in any combination for the purpose of staging parties. By the second half of the decade, custom-built systems began to appear from the workshops of specialists such as Headley Jones, who constructed wardrobe-sized speaker cabinets known as "House of Joy." It was also around this time that Jamaica's first superstar DJ and MC, Count Machuki (b. Winston Cooper) rose to prominence. As time progressed, sound systems became louder--capable of playing bass frequencies of 30,000 watts or more, with similar wattage attainable at the mid-range and high frequencies--and far more complex than their predecessors, record players with a single extension speaker. Competition between these sound systems was fierce, and eventually two DJs emerged as the stars of the scene: Clement 'Coxsone' Dodd, and Duke Reid.
The popularity of a sound system was mainly contingent on one thing: having new music. In order to circumvent the release cycle of the American record labels, the two sound system superstars turned to record production. Initially, they produced only singles for their own sound systems, known as "Exclusives" or Dubplates - a limited run of one copy per song. What began as an attempt to copy the American R&B sound using local musicians evolved into a uniquely Jamaican musical genre: ska. This shift was due partly to the fact that as American-style R&B was embraced by a largely white, teenage audience and evolved into rock and roll, sound system owners could no longer depend on a steady stream of the singles they preferred: fast-shuffle boogies and ballads. In response to this shift in supply, Jamaican producers introduced to their work some of the original elements of the Jamaican sound: rhythm guitars strumming the offbeat and snare-drum emphasis on the third beat, for example. As this new musical form became more popular, both Dodd and Reid began to move more seriously into music production. Coxsone Dodd's production studio became the famous Studio One, while Duke Reid founded Treasure Isle.
As sound systems continued to gain in popularity through the 1960s and 1970s, they became politicized in many instances. Many sound systems, and their owners, were labeled as supporters of a particular political party (such as the PNP or the JLP), but most of the sound systems tried to maintain political neutrality. Nevertheless, as a cultural and economic phenomenon, the sound system was affected by the vast socio-political changes taking place in Jamaica at this time.
Taken From: http://en.wikipedia.org/wiki/Sound_system_(Jamaican)