Well instead of buying a shiva or a tempest I am going to us a sub I bought for car use. An Eclipse 8600 series 12. A dvc, 4 ohm coils. Fs is 28hz, RMS is 170w. Xmax one way is .99". I am going to try it in the 8 cubic foot box that I was planning on putting a tempest it. But the question for today is...How many ports should I use? 2 4" round? Bigger? Smaller? I plan on tuning to the good old 20hz. Oh, if this sub doesn't work out, I plan on buying a tempest and putting it in the same box.