A few books that you may find useful:

Davis, Gary and Ralph Jones. 1989. The Sound Reinforcement Handbook (Yamaha). (2nd ed.) Hal Leonard Publishing. Milwaukee, WI. (Classic, very complete guide, including many technical details))

Fry, Duncan R. 1992. Live Sound Mixing (2nd ed.) Roztralia Publications, Victoria, Australia. Available from: ShedWorks, 4411 Brookford Ave., Woodland Hills, CA 91364 (818)225-1809. (Easily followed, non-technical guide for aspiring concert sound engineers covering all the basics with useful hints)

Moscal, Tony. 1994. Soundcheck: The Basics of Sound and Sound Systems. Hal Leonard Publishing. Milwaukee, WI. (Concise breezy guide to sound system components, with few technical details).

Rumsey, Francis and Tim McCormick. 1994. Sound and Recording: an Introduction (2nd ed.) Focal Press, Oxford, UK (Solid, basic audio components descriptions, with focus on recording rather than live sound)