Gear & technology
Passive radiator
Also called drone cone, passive driver
A passive radiator is a driver with no motor, just a cone and suspension, mounted in a speaker cabinet to do the job of a port. Air pressure from the active driver moves it, adding bass without the noise of a port tube.
It works like a Bass reflex port tuned by mass rather than by air in a tube, which suits small cabinets where a port long enough for a low tuning would not fit. Compact Wireless speakers and small subwoofers often use one or two, sometimes with visible weights to set the tuning.
Compared with a port there is no chuffing and no pipe resonance, but the radiator adds cost and the roll-off below tuning is steeper still. The sound is otherwise much like a ported speaker.