Purifi Audio PTT5.25PR-NF2-01 5.25" Passive Radiator incorporates PURIFI’s Neutral Surround technology in order to eliminate Surround Radiation Distortion. With its low-distortion properties, long linear stroke and tunable mass, the driver is eminently suited as a companion to PTT5.25W especially in compact speaker construction where a traditional reflex port would limit the performance.