Dont know what size you have, but here are the reccommended enclosure sizes for the 10, 12, and 15" Power HX2's:
10"
Sealed box -
Recommended Volume (Cubic feet) - .625
Ported box -
Recommended Volume (Cubic feet) - 1.75
F3(Hz) - 33
Number of Ports - 3
Port diameter(Inches) - 3
Port Length(Inches) - 16.5
12"
Sealed box -
Recommended Volume (Cubic feet) - 1.0
Ported box -
Recommended Volume (Cubic feet) - 2.5
F3(Hz) - 40
Number of Ports - 2
Port diameter(Inches) - 4
Port Length(Inches) - 12.65
15"
Sealed box -
Recommended Volume (Cubic feet) - 1.25
Ported box -
Recommended Volume (Cubic feet) - 3.5
F3(Hz) - 33
Number of Ports - 4
Port diameter(Inches) - 4
Port Length(Inches) - 18
- Steve