For a sedan, one sub, 400 W. It’s the same math as the designer’s step-by-step mode, where you can fit the box to your space, vehicle and amp and get plans, a cut sheet and DXF.
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain
Thiele/Small parameters
Fs
32 Hz
Qts
1.13
Qes
1.401
Qms
5.81
Vas
1.59 ft³
Re (one coil)
3.6 Ω
Sd
≈ 76 in²
Xmax
≈ 0.39″
EBP
23 — suits sealed calc.
Sensitivity, 1 W / 1 m
82.2 dB calc.
General
Size
12″
Voice coils
dual 4 Ω
RMS power
400 W
Mounting dimensions
Cutout diameter
≈ 10 7/8″
Mounting depth
6″
Overall diameter
12 1/16″
“≈” means the value isn’t in the spec sheet and a typical value for the size is used; “calc.” means it’s calculated from the published parameters. Check the manufacturer’s spec sheet before you build.