It doesn't have to be. They let you choose 1, 2, or 4 ohms with that sub+box combo. It's whatever ohms the OP chooses for the subs that he'll have to find a 2000w rms (minimum) amp for. It's usually more cost effective to find an amp that puts out that kind of power at 1 ohm than an amp that does it at 2 or 4 ohms.Why does it have to be @ 1 ohm? There are amps that put out the same power at 2 ohms.