I'm looking to build my first DIY sub and have decided on the 24" cube enclosure w/ AV15 + 2 18" pr's. Problem is, I want to build 2 of these subs but stryke only has 2 18" pr's (I need 4). I will build one sub with the 2 18" pr's but not sure what to do with the other sub. So my question is, how do I make a sub that's ROUGHLY equivalent to the AV15 + 2 18" pr design without having the 2 18"pr's? Can I instead use 3 15" PR's? Is a port possible in this scenario given I have to stick with a 24" cube enclosure? If so, can anyone give any suggestions on the diameter, length, and the number of ports needed to build it.