A loudspeaker, speaker, or speaker system is an electromechanical transducer which converts an electrical signal into sound. The term loudspeaker is currently used for both individual devices and for complete systems consisting of one or more drivers (as the individual transducers are often called) in an enclosure, often with a crossover circuit. Their cost may range from pennies in a cheap radio to high-fidelity speaker systems costing many thousands of dollars. Loudspeakers are the most variable elements in any audio system, regardless of cost, and are responsible for marked audible differences between otherwise identical sound systems. (wikipedia)