well shit then that means i can fill the back then lol doubt i can get 20 cu ft lemme check that 5 cu ft is the max size for a ported box
heres the specs
Size (IN.,CM) 15, 38.1
Impedance (OHMS) 2 or 4 DVC
Max Rec Amplifier Power (WATTS PEAK/RMS)* 1000/500
Sensitivity (dB 1w/1m) 89.1
Frequency Response (Hz) 25-500
Mounting Depth (IN.,CM) 8 1/8, 20.6
Mounting Cutout (IN.,CM) 13 7/8, 35.2
Min Rec Sealed Box Volume (CU. FT., Liters) 1.8, 51
Max Rec Sealed Box Volume (CU. FT., Liters) 5.2, 147
Min Rec Vented Box Volume (CU. Ft., Liters)** 3, 85
Max Rec Vented Box Volume (CU. Ft., Liters)** 5, 142