Power amplifiers are the driving force behind all “passive” speakers. Passive speakers are speaker cabinets that do no posses their own built in amplification and thus rely on external sources of power- such as an amplifier. There are distinct advantages to passive PA systems, as it allows you the flexibility to move your amp rack to a location apart from the speakers. This could be really important if you’re setting up sound for an outdoor venue that has a lot of direct sunlight and could cause your self-powered speakers to overheat. It also makes it significantly easier to compose a rack chain of outboard gear, such as compressors, eq’s, zone mixers and such for better signal chain processing and audio distribution.