A speaker enclosure using a passive radiator usually contains an "active", or main driver, and a "passive radiator" . The active driver is a regular driver, and the passive is typically the same or similar, but without a voice coil or magnet assembly. It is only a suspended cone, not attached to a voice coil or electrical circuit.
Passive radiators are used instead of a reflex port for much the same reasons - to tune the small volume and driver for better low frequency performance improved power handling and sound quality. They are also used to eliminate port turbulence and reduce motion compression caused by high velocity airflow in small ports. Passive radiators are tuned by mass variations, changing the way their compliance interacts with motion of the air in the box.
InPhase PR12 Features - Driver 1 x 12"
- Impedance 4 Ohm
- Sensitivity 91 dB
- Peak Power 1400W
- Frequency response 28-200Hz
- Dimension (H x W x D): 509mm x 355mm x 327mm