The ability of a single speaker to be driven by two separate amplifiers. Generally this is accomplished by having two sets of inputs on the back of the speaker, one going to the tweeter high-pass filter and one going to the woofer low-pass filter. It is also possible in 3 or more-way systems by combining the tweeter and midrange into one section, etc. This method can be used to allow separately adjustable levels for the treble and bass, but is not guaranteed to produce positive results.