Passive radiators have to be out of phase but drivers can be wired to make them in phase to compensate for the crossover.
Aren't passive radiators out of phase?
Passive radiators seem like a great idea, but they must be out of phase with the driver. Yet, you see them on some pretty good speakers, such as the Sunfire subs. All I can think is they provide a spring-board, storing energy for the driver. Still, any sound produced by the PR is out of phase though. Any thoughts?