PA speakers project the amplified sound out to the audience and at the entry level end of the market most PA speakers are simply called 'Full Range Speakers' as they are designed to handle the complete range of sound frequencies. However, with Sound Reinforcement Systems the frequencies become more detached and are routed to specific types of speaker enclosures by cross-over devices which are types of audio routing filters.
In larger theatre type SR systems speaker enclosures are used that have been specifically designed to handle a defined type of audio frequency. Bass frequencies are electronically routed to a large 15" or 18" speaker within enclosures called "Bass Bins". Likewise mid-range and high frequencies are routed to High Frequency Horns and Mid-Range Compression drivers. Systems constructed with this electronic routing and filtering capability are generally referred to as "Active" systems.
