Fi Audio SP4 18v2+ D1

18″ subwoofer · dual 1 Ω · 3,500 W RMS

Fs 24.6 HzQts 0.37Vas 5.29 ft³Xmax 1.30″

Recommended box

For a sedan, one sub, 3,500 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

Net volume2.38 ft³ (67.5 L)
Qtc0.67
Fc44 Hz
F3 (−3 dB, no cabin gain)49 Hz
Example box (outside)20 1/16″ × 20 1/16″ × 14 5/8″
Open sealed box in designer

Ported

Net volume4.73 ft³ (134 L)
Tuning (Fb)28 Hz
Portslot 4 15/16 × 19 7/16″, 60 7/8″ long
Port velocity at 3,500 W65 ft/s
F3 (−3 dB, no cabin gain)27 Hz
Example box (outside)31 1/2″ × 20 7/8″ × 27 1/4″
Open ported box in designer
203040506080100150200667278849096HzdB
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Fs24.6 Hz
Qts0.37
Qes0.39
Qms9.44
Vas5.29 ft³
Re (one coil)0.65 Ω
Sd187.6 in²
Xmax1.30″
Vd243.7 in³ calc.
Mms579 g calc.
BL12.2 T·m calc.
EBP63 — sealed or ported calc.
Sensitivity, 1 W / 1 m89.6 dB calc.

General

Size18″
Voice coilsdual 1 Ω
RMS power3,500 W

Mounting dimensions

Ø18 1/2″cutout Ø16 3/4″mounting depth 12 1/4″magnet Ø≈ 10 7/8″
Cutout diameter16 3/4″
Mounting depth12 1/4″
Overall diameter18 1/2″

“≈” 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.

Data sources

Other Fi Audio 18″ models