For a sedan, one sub, 350 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
43.8 Hz
Qts
0.70
Qes
0.753
Qms
9.3
Vas
0.40 ft³
Re (one coil)
1.95 Ω
Sd
41.7 in²
Xmax
0.44″
Vd
18.5 in³ calc.
Mms
120 g calc.
BL
9.2 T·m calc.
EBP
58 — sealed or ported calc.
Sensitivity, 1 W / 1 m
83 dB calc.
General
Size
8″
Voice coils
dual 2 Ω
RMS power
350 W
Mounting dimensions
Cutout (square, side)
7 3/8″
Mounting depth
2 3/4″
Magnet diameter
5 11/16″
“≈” 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.