passive loudspeaker box

Passive boxes are speaker boxes whose speakers are supplied by an external power amplifier. In contrast, active speakers have one or more power amplifiers built into the speaker cabinet.

The different speakers of a passive speaker - tweeter, midrange, woofer - are driven by a single power amplifier and the frequencies are separated by a crossover with high pass, band pass and low pass. The tweeter receives only frequencies above about 2 kHz to 4 kHz via a high-pass filter, the midrange driver receives frequencies between a few hundred Hertz and a few kilohertz, depending on the design, and the woofer receives frequencies below a few hundred Hertz.