For a sedan, one sub, 250 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
23 Hz
Qts
0.40
Qes
0.422
Qms
9.61
Vas
7.99 ft³
Re
3.32 Ω
Sd
≈ 124 in²
Xmax
0.53″
EBP
55 — sealed or ported calc.
Sensitivity, 1 W / 1 m
90.1 dB calc.
General
Size
15″
Voice coils
4 Ω
RMS power
250 W
Mounting dimensions
Cutout diameter
13 11/16″
Mounting depth
7 7/16″
Overall diameter
15 1/2″
Magnet diameter
6 5/16″
“≈” 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.