I was over at a friend's house recently and was quite impressed with his old M&K sub. It has 2 12" drivers which are both active in what they call a "push-pull" configuration. This to me would seem exactly the same as "out of phase" with one driver going in while the other moves out.
How does a push-pull config work ? Wouldn't you get less bass with the cancellation of them working out of phase ?
It obviously works very well but I can't fathom how push-pull adds bass and doesn't reduce it...