BeeMan, thanks, yes I understand the dual 15's vs single 18" and yes Steve all things equal bigger driver should be better than smaller driver but in this case the 15" is designed better than the 18" so it will outperform the 18" ..cool, makes sense...but having said that...is there an 18" in this price range that is up to task because..., getting back to BeeMan's example, it would be even better to have those dual 18's instead of dual 15"s. The 4645 I'm pretty much ruling out due to the low end not being where I feel I would be happy. BTW, I just finished viewing a video on youtube on the Rythmik F15s...very impressive.
One other thing that I have always believed is that a sealed sub is better...keep in mind now I'm 53 years old so I've seen a lot of this stuff from way back in the day where sealed woofers ruled, horn loaded woofers respected, and porting was a new thing so the idea of a sealed sub is attractive
Have a Happy and safe New Year!!!