 PR speakers are only slightly more complex to design and are generally more expensive as compared to standard bass reflex enclosures.Passive radiators are used in Bluetooth speakers, home stereo speakers, subwoofer cabinets and car audio speaker systems, particularly in cases where there is not enough space for a port or vent system.While most studio monitor speakers are either ported bass reflex designs, or closed-back without a vent or passive radiator, Mackie's HR824 and HR624 monitor speakers have a passive radiator installed on the rear of the cabinet.