Fi Audio BTL4 18 D2

18″ subwoofer · dual 2 Ω · 3,500 W RMS

Fs 25 HzQts 0.51Vas 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 volume3.71 ft³ (105 L)
Qtc0.80
Fc39 Hz
F3 (−3 dB, no cabin gain)37 Hz
Example box (outside)31 1/2″ × 20 7/8″ × 13 3/16″
Open sealed box in designer

Ported

Net volume7.27 ft³ (206 L)
Tuning (Fb)26 Hz
Port2 round ports Ø5″, 17 11/16″ long
Port velocity at 3,500 W186 ft/s
F3 (−3 dB, no cabin gain)23 Hz
Example box (outside)31 1/2″ × 20 7/8″ × 25 1/16″
Open ported box in designer
203040506080100150200667278849096HzdB
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Fs25 Hz
Qts0.51
Qes0.55
Qms7.59
Vas5.33 ft³
Re (one coil)1.4 Ω
Sd187.6 in²
Xmax1.30″
Vd243.7 in³ calc.
Mms557 g calc.
BL14.9 T·m calc.
EBP45 — suits sealed calc.
Sensitivity, 1 W / 1 m88.3 dB calc.

General

Size18″
Voice coilsdual 2 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