The passive radiator (or passive loudspeaker) is integrated in a box with an active loudspeaker. This passive radiator, if at first sight it can look like a "classic" loudspeaker, does not in fact have any motor part. Thus, we will not find in its design a coil, a magnet and a 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 membrane and restore sound, thus providing deep bass. Its resonance frequency is determined by its mass and the air contained in the cabinet. We can therefore vary its resonance frequency on many models and tune it to the speaker by adding mass.