Seas Passiv radiators
Passive radiators should be used like bass reflex tubes. The resonance of the passive radiator instead of the bass reflex tube is being used. Seas passive radiators are very versatile. For tuning purpose weights may be screwed to the back of the drivers. The passive membrane area should ideally be the same size as the one of the active driver or up to 50% bigger under heavy loads. This is because the moved air by the passive radiator is - depending on the frequency - up to 50% higher than the one by the active driver.