Sky High Car Audio FXB-12 D4

12″ subwoofer · dual 4 Ω · 1,500 W RMS

31.4 HzFs, resonance

0.68Qts

1.02 ft³Vas

1.18″Xmax

1,500 WRMS

Source	skyhighcaraudio.com · manufacturer data
Checked against source	October 2026
Thiele/Small parameters	complete
Mounting dimensions	3 of 4 — missing: magnet diameter; the designer will use an estimate

Recommended box

For a sedan, one sub, 1,500 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

smaller, tighter

1.87 ft³ (53 L)

Net volume

Bass character (Qtc)	Tight and punchy · 0.85
Fc	39 Hz
F3 (−3 dB, no cabin gain)	35 Hz
Example box (outside)	14 3/16″ × 14 3/16″ × 22 7/16″

Open sealed box in designer

Ported

deeper, louder

1.31 ft³ (37 L)

Net volume

Tuning (Fb)	34 Hz
Port	slot 1 3/4 × 14 5/16″, 40 3/4″ long
Port velocity at 1,500 W	83 ft/s
F3 (−3 dB, no cabin gain)	30 Hz
Example box (outside)	20 13/16″ × 15 3/4″ × 15 3/16″

At 1,500 W this example’s port will be noisy: air speed 83 ft/s, while the limit is 82 ft/s. It stays quiet up to about 1,450 W. Full power needs a port of at least 25.6 in², which means a bigger box than this example — size it in the designer.

Open ported box in designer

Deeper: 3.18 ft³ (90 L) tuned to 26 Hz, 31 1/2″ × 15 3/4″ × 23 1/4″ outside — a bigger box with flatter deep bass. Open in the calculator

Where to buy Amazon

Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Size	12″
Voice coils	dual 4 Ω
RMS power	1,500 W
Fs	31.4 Hz
Qts	0.68
Qes	0.76
Qms	6.71
Vas	1.02 ft³

Re (one coil)	3.2 Ω
Sd	81.8 in²
Xmax	1.18″
Vd	96.6 in³ calc.
Mms	351 g calc.
BL	17.1 T·m calc.
EBP	41 — suits sealed calc.
Sensitivity, 1 W / 1 m	82.7 dB calc.

Mounting dimensions

Cutout diameter	11 1/8″
Mounting depth	7 15/16″
Overall diameter	12 13/16″

Cone area (Sd) calculated from Fs, Vas and Mms: 81.8 in².

“≈” 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

skyhighcaraudio.com/sky-high-car-audio-fxb-series-12-subwoofer/

Other Sky High Car Audio 12″ models

Sky High Car Audio BMX-12 D1 12″ · dual 1 Ω
Sky High Car Audio BMX-12 D2 12″ · dual 2 Ω
Sky High Car Audio FE-12 D2 12″ · dual 2 Ω
Sky High Car Audio FE-12 D4 12″ · dual 4 Ω
Sky High Car Audio FEX-12 D2 12″ · dual 2 Ω
Sky High Car Audio FEX-12 D4 12″ · dual 4 Ω
Sky High Car Audio FMX-12 D1 12″ · dual 1 Ω
Sky High Car Audio FMX-12 D2 12″ · dual 2 Ω
Sky High Car Audio FXB-12 D2 12″ · dual 2 Ω
Sky High Car Audio FXXL-12 D1 12″ · dual 1 Ω
Sky High Car Audio FXXL-12 D2 12″ · dual 2 Ω

Similar 12″ subwoofers from other brands

Close in Fs, Qts and Vas — a box of similar volume will suit them.

Ground Zero GZRW 12XSPL (2x2 Ohm) 1.77 ft³ sealed · 1.24 ft³ ported
Alpine SWR-T12 (Type-R thin) 1.73 ft³ sealed · 1.20 ft³ ported
DD Audio 512e D2 1.73 ft³ sealed · 2.26 ft³ ported
DD Audio 512e D4 1.73 ft³ sealed · 2.26 ft³ ported
JL Audio 12TW3-D8 1.91 ft³ sealed · 0.95 ft³ ported
Diamond DES122 1.77 ft³ sealed · 1.24 ft³ ported

FAQ

What box does the Sky High Car Audio FXB-12 D4 need?

Recommended net volume: 1.87 ft³ sealed, 1.31 ft³ ported tuned to 34 Hz — for one sub in a sedan at 1,500 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.

What are the Sky High Car Audio FXB-12 D4 Thiele/Small specs?

Fs 31.4 Hz, Qts 0.68, Vas 1.02 ft³, Xmax 1.18″, Sd 81.8 in².

What is the Sky High Car Audio FXB-12 D4 mounting depth?

Mounting depth is 7 15/16″, cutout diameter 11 1/8″. The inside depth of the box must exceed the mounting depth by at least 1″.

How much power does the Sky High Car Audio FXB-12 D4 handle and how do I wire it?

RMS power rating: 1,500 W. Dual 4 Ω voice coils: series gives 8 Ω, parallel gives 2 Ω at the amp. Wiring for several subs and amp power — in the wiring calculator.