The Sundown Z15 was designed as an "SQL" subwoofer -- meaning that it has great sound quality with the potential to get loud as well. They are rated for 1000-watts RMS and work great sealed OR ported.

Sealed : 2 - 2.5 cubes
Ported : 2.75 - 3.25 cubes tuned to 30-35 Hz

D2 specifications are nearly identical to D4.

Fo= 28.585 Hz
Sd= 83.000m M2
Krm= 6.988m Ohm
Erm= 0.927
Kxm= 133.190m H
Exm= 0.630
Vas= 105.275 L
Cms= 107.617 uM/N
Mms= 288.070 g
BL= 26.107 T·M
Qms= 5.000
Qes= 0.467
Qts= 0.427