Sky High Car Audio FMX-15 D2

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

20.9 HzFs, resonance

0.42Qts

2.98 ft³Vas

1.46″Xmax

3,500 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, 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

smaller, tighter

1.48 ft³ (42 L)

Net volume

Bass character (Qtc)	Flat and accurate · 0.73
Fc	36 Hz
F3 (−3 dB, no cabin gain)	37 Hz
Example box (outside)	16 15/16″ × 16 15/16″ × 13 5/16″

Open sealed box in designer

Ported

deeper, louder

2.40 ft³ (68 L)

Net volume

Tuning (Fb)	30 Hz
Port	slot 2 3/4 × 16 5/16″, 50″ long
Port velocity at 3,500 W	99 ft/s
F3 (−3 dB, no cabin gain)	27 Hz
Example box (outside)	31 1/2″ × 17 11/16″ × 16″

At 3,500 W this example’s port will be noisy: air speed 99 ft/s, while the limit is 82 ft/s. It stays quiet up to about 2,350 W. Full power needs a port of at least 54.3 in², which means a bigger box than this example — size it in the designer.

Open ported box in designer

Deeper: 3.74 ft³ (106 L) tuned to 25 Hz, 31 1/2″ × 17 11/16″ × 24 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	15″
Voice coils	dual 2 Ω
RMS power	3,500 W
Fs	20.9 Hz
Qts	0.42
Qes	0.467
Qms	4.29
Vas	2.98 ft³

Re (one coil)	1.29 Ω
Sd	122.7 in²
Xmax	1.46″
Vd	178.8 in³ calc.
Mms	611 g calc.
BL	14.9 T·m calc.
EBP	45 — suits sealed calc.
Sensitivity, 1 W / 1 m	84.2 dB calc.

Mounting dimensions

Cutout diameter	13 3/4″
Mounting depth	10 13/16″
Overall diameter	15 1/2″

Judging by its value, the published Re is for both coils in series — converted to per coil.

“≈” 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-fmx-series-15-subwoofer/

Other Sky High Car Audio 15″ models

Sky High Car Audio BMX-15 D1 15″ · dual 1 Ω
Sky High Car Audio BMX-15 D2 15″ · dual 2 Ω
Sky High Car Audio FE-15 D2 15″ · dual 2 Ω
Sky High Car Audio FE-15 D4 15″ · dual 4 Ω
Sky High Car Audio FEX-15 D2 15″ · dual 2 Ω
Sky High Car Audio FEX-15 D4 15″ · dual 4 Ω
Sky High Car Audio FMX-15 D1 15″ · dual 1 Ω
Sky High Car Audio FXB-15 D2 15″ · dual 2 Ω
Sky High Car Audio FXB-15 D4 15″ · dual 4 Ω
Sky High Car Audio FXXL-15 D1 15″ · dual 1 Ω
Sky High Car Audio FXXL-15 D2 15″ · dual 2 Ω

Similar 15″ subwoofers from other brands

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

Diamond HXP152 1.36 ft³ sealed · 2.40 ft³ ported
Sundown Audio Xv1-15 D2 1.48 ft³ sealed · 2.58 ft³ ported
Alpine SWR-1522D (Type-R) 1.25 ft³ sealed · 2.83 ft³ ported
RE Audio XX15 D2 v2 1.77 ft³ sealed · 2.86 ft³ ported
RE Audio XX15 D4 v2 1.77 ft³ sealed · 2.86 ft³ ported
Diamond HXP154 1.59 ft³ sealed · 2.40 ft³ ported

FAQ

What box does the Sky High Car Audio FMX-15 D2 need?

Recommended net volume: 1.48 ft³ sealed, 2.40 ft³ ported tuned to 30 Hz — for one sub in a sedan at 3,500 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 FMX-15 D2 Thiele/Small specs?

Fs 20.9 Hz, Qts 0.42, Vas 2.98 ft³, Xmax 1.46″, Sd 122.7 in².

What is the Sky High Car Audio FMX-15 D2 mounting depth?

Mounting depth is 10 13/16″, cutout diameter 13 3/4″. The inside depth of the box must exceed the mounting depth by at least 1″.

How much power does the Sky High Car Audio FMX-15 D2 handle and how do I wire it?

RMS power rating: 3,500 W. Dual 2 Ω voice coils: series gives 4 Ω, parallel gives 1 Ω at the amp. Wiring for several subs and amp power — in the wiring calculator.