Sound Reinforcement Speakers
There isn't anything technically unique about sound reinforcement loudspeakers. Basically they are like any other type of speaker, with some general characteristics specific to this type of work...
Just like home entertainment systems, sound reinforcement systems use different speakers for different frequency ranges. High frequencies are handled by smaller speakers and horns, middle and lower frequencies are handled by larger cone drivers.
These speakers need to be capable of handling high wattage, and are generally rated at hundreds of watts.
A popular size for sound reinforcement speakers is 15 inches, although 12-18 inches are also common. For more volume, more speakers are used (rather than bigger speakers).
Especially in lower frequencies, these speakers need to move large volumes of air. Various cabinet designs have been developed to assist in this, including the venerable "w-bin" for punchy bass.