A speaker system, particularly useful as a subwoofer, comprises an enclosure with one acoustic transducer facing to the right and one acoustic transducer facing to the left, which effectively cancels out transducer cone mass induced vibration within the enclosure. The enclosure also has one passive radiator facing up and one passive radiator facing down. The passive radiator facing down effectively couples acoustic energy at very low frequencies into the floor. The passive radiators each have a rather a large area and high mass. The large, high mass, bottom mounted passive radiator will produce large amounts of enclosure vibration, and so to cancel this vibration, the upper passive radiator is of substantially the same mass and size. The resulting system will be vibrationally balanced on all axes while simultaneously effectively coupling low frequency energy onto the floor of the listening room with good efficiency.