When multiple drivers are used in a system, a "filter network", called a crossover, is used to separate the incoming signal into different frequency bands appropriate for each driver. A loudspeaker system with n separate frequency bands is described as "n-way speakers": a 2-way system will have woofer and tweeter speakers; a 3-way system is either a combination of woofer, mid-range and tweeter or subwoofer, woofer and tweeter.
The modern design of moving-coil drivers was established by Oliver Lodge in (1898). The moving coil principle was patented in 1924 by Chester W. Rice and Edward W. Kellogg.
