A kind of closed enclosure, mainly adds another low frequent speaker.When it vibrates to generate sound, the passive radiator diaphragm is pushed by air.

• 属于密闭式音箱，主要多增加一支只有振膜的单体(低音单体，当低音振动发声时，其藉由空气来推动背辐式振膜的延伸。