 It is not attached to a voice coil or wired to an electrical circuit or power amplifier.In the same way as a ported loudspeaker, a passive radiator system uses the sound otherwise trapped in the enclosure to excite a resonance that makes it easier for the speaker system to create the deepest pitches (e.g., basslines).The passive radiator resonates at a frequency determined by its mass and the springiness of the air in the enclosure.