Fi Audio BTL4 18 D1

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

Fs 24.8 HzQts 0.52Vas 5.33 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 volume3.96 ft³ (112 L)
Qtc0.80
Fc38 Hz
F3 (−3 dB, no cabin gain)36 Hz
Example box (outside)31 1/2″ × 20 7/8″ × 13 15/16″
Open sealed box in designer

Ported

Net volume7.27 ft³ (206 L)
Tuning (Fb)26 Hz
Portslot 5 11/16 × 19 7/16″, 51 5/8″ long
Port velocity at 3,500 W65 ft/s
F3 (−3 dB, no cabin gain)23 Hz
Example box (outside)31 1/2″ × 20 7/8″ × 34 7/16″
Open ported box in designer
203040506080100150200667278849096HzdB
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Fs24.8 Hz
Qts0.52
Qes0.56
Qms7.61
Vas5.33 ft³
Re (one coil)0.7 Ω
Sd187.6 in²
Xmax1.30″
Vd243.7 in³ calc.
Mms566 g calc.
BL10.5 T·m calc.
EBP44 — suits sealed calc.
Sensitivity, 1 W / 1 m88.1 dB calc.

General

Size18″
Voice coilsdual 1 Ω
RMS power3,500 W

Mounting dimensions

Ø18 1/2″cutout Ø16 3/4″mounting depth 9 1/2″magnet Ø≈ 10 7/8″
Cutout diameter16 3/4″
Mounting depth9 1/2″
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