How a passive radiator works

The passive radiator (or passive loudspeaker) fits into a box with an active loudspeaker. This passive radiator, although it may at first glance look like a "classic" loudspeaker, does not in fact have any engine parts. Thus, its design does not include a coil, magnet and power supply. In the same way, it will not be electrically connected to a power amplifier.

To diffuse sound, the passive radiator will use the air pressures and depressions induced by the active loudspeaker in the cabinet to vibrate its diaphragm and restitute sound, thus providing deep bass. Its resonant frequency is determined by its mass and contained in the cabinet. Therefore, on many models, its resonance frequency can be varied and tuned to the speaker by adding mass.