I'm only going on the research I've done online...
Go with the ACI Force or VTF-3. The VTF-3 extends lower, I believe, but is also very quick and musical. It goes as low as 16 hertz and is supposed to be very accurate. The ACI Force is supposed to be a wonderful musical sub but I don't believe it goes quite as low. Its about a 100 dollar difference, right? (not sure about shipping and handling for the ACI Force)
You might want to consider the UFW-12 from Onix, when that comes out. I doubt it'll be MUCH different than the VTF-3...but comparisons to the ACI Force were made with the UFW-10. The 12 will go lower and should be as quick as the 10.
The VMPS Larger Sub is supposed to be pretty good too, but requires an amp as its a passive design.
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