Sky High Car Audio FMX-8 D1

8″ subwoofer · dual 1 Ω · 800 W RMS

44.3 HzFs, resonance

0.59Qts

0.17 ft³Vas

0.71″Xmax

800 WRMS

The Sky High Car Audio FMX-8 D1 is a 8″ subwoofer. With Qts 0.59 and EBP 67 it works both sealed and ported: sealed is tighter and smaller, ported is deeper and louder. Long excursion (Xmax 0.71″) — built for loud music and high power.

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, 800 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

0.35 ft³ (10 L)

Net volume

Bass character (Qtc)	Flat and accurate · 0.72
Fc	54 Hz
F3 (−3 dB, no cabin gain)	55 Hz
Example box (outside)	10 5/8″ × 10 5/8″ × 9 5/16″

Open sealed box in designer

Ported

deeper, louder

0.46 ft³ (13 L)

Net volume

Tuning (Fb)	41 Hz
Port	slot 1 15/16 × 14 5/16″, 93 5/16″ long
Port velocity at 800 W	42 ft/s
F3 (−3 dB, no cabin gain)	35 Hz
Example box (outside)	31 1/2″ × 15 3/4″ × 10 3/8″

The volume and tuning are the recommendation, but the port doesn’t fit this example box. Size the box and port in the designer.

Open ported box in designer

Deeper: 0.57 ft³ (16 L) tuned to 33 Hz, 31 1/2″ × 15 3/4″ × 12 1/2″ 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	8″
Voice coils	dual 1 Ω
RMS power	800 W
Fs	44.3 Hz
Qts	0.59
Qes	0.66
Qms	5.69
Vas	0.17 ft³

Re (one coil)	0.9 Ω
Sd	29.1 in²
Xmax	0.71″
Vd	20.6 in³ calc.
Mms	131 g calc.
BL	7.1 T·m calc.
EBP	67 — sealed or ported calc.
Sensitivity, 1 W / 1 m	80.1 dB calc.

Mounting dimensions

Cutout diameter	7 1/2″
Mounting depth	6 9/16″
Overall diameter	8 3/4″

Where it fits in a vehicle

Spots from our vehicle guides where the cutout, mounting depth and recommended box fit. The spot sizes are approximate — measure your own vehicle.

F-150 SuperCrew — under the rear seat sealed and ported box
Ram Crew Cab — under the rear seat sealed and ported box
Tacoma Double Cab — under the rear seat sealed and ported box
Bronco 4-door — behind the rear seat sealed and ported box
Wrangler 4-door, hard top — behind the rear seat sealed and ported box
Wrangler 4-door, soft top — behind the rear seat sealed and ported box
Silverado / Sierra Crew Cab — under the rear seat sealed and ported box
Spare tire well sealed and ported box
Polaris RZR / Ranger — under the seat sealed and ported box
Can-Am — under the seat sealed and ported box
FJ Cruiser — behind the rear seat sealed and ported box
El Camino 1978–87 — behind the seat sealed and ported box
Cherokee XJ — cargo area, spare moved out sealed and ported box
Excursion — behind the third row sealed and ported box
Mustang 2015–2023 coupe — trunk sealed and ported box
Challenger / Charger — trunk sealed and ported box
Tesla Model 3 — well under the trunk floor sealed and ported box
Club Car Precedent — under the rear seat sealed and ported box

Cone area (Sd) calculated from Fs, Vas and Mms: 29.1 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-fmx-series-8-subwoofer/

Voice coil versions

The same sub with different voice coils: the parameters are nearly the same — pick by your amp and wiring.

Model	Voice coils	Re	Qes	Vas	Sealed	Ported
Sky High Car Audio FMX-8 D1	dual 1 Ω	0.9 Ω	0.66	0.17 ft³	0.35 ft³	0.46 ft³ · 41 Hz
Sky High Car Audio FMX-8 D2	dual 2 Ω	1.9 Ω	0.55	0.16 ft³	0.35 ft³	0.46 ft³ · 42 Hz

Other Sky High Car Audio 8″ models

Sky High Car Audio BMX-8 D1 8″ · dual 1 Ω
Sky High Car Audio BMX-8 D2 8″ · dual 2 Ω
Sky High Car Audio FE-8 D2 8″ · dual 2 Ω
Sky High Car Audio FE-8 D4 8″ · dual 4 Ω
Sky High Car Audio FXB-8 D2 8″ · dual 2 Ω
Sky High Car Audio FXB-8 D4 8″ · dual 4 Ω

Similar 8″ subwoofers from other brands

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

DD Audio 2508g ESP D2 0.39 ft³ sealed · 0.99 ft³ ported
DD Audio 2508g ESP D4 0.39 ft³ sealed · 0.99 ft³ ported
Sundown Audio SDv3-8 D4 0.25 ft³ sealed · 0.46 ft³ ported
Skar Audio SVR-8 D4 0.28 ft³ sealed · 0.67 ft³ ported
SoundQubed HDS2.208 D2 0.30 ft³ sealed · 0.49 ft³ ported
SoundQubed HDS2.208 D4 0.30 ft³ sealed · 0.49 ft³ ported

FAQ

What box does the Sky High Car Audio FMX-8 D1 need?

Recommended net volume: 0.35 ft³ sealed, 0.46 ft³ ported tuned to 41 Hz — for one sub in a sedan at 800 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-8 D1 Thiele/Small specs?

Fs 44.3 Hz, Qts 0.59, Vas 0.17 ft³, Xmax 0.71″, Sd 29.1 in².

What is the Sky High Car Audio FMX-8 D1 mounting depth?

Mounting depth is 6 9/16″, cutout diameter 7 1/2″. 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-8 D1 handle and how do I wire it?

RMS power rating: 800 W. Dual 1 Ω voice coils: series gives 2 Ω, parallel gives 0.5 Ω at the amp. Wiring for several subs and amp power — in the wiring calculator.

Is the Sky High Car Audio FMX-8 D1 better sealed or ported?

EBP 67: both work — sealed 0.35 ft³ is tighter and smaller, ported 0.46 ft³ tuned to 41 Hz is deeper and louder.

What port does the Sky High Car Audio FMX-8 D1 need?

For the 0.46 ft³ ported box tuned to 41 Hz: slot 1 15/16 × 14 5/16″, 93 5/16″ long, area 28.2 in²; or a round port Ø6″, ≈ 93 5/16″ long. Port air speed at 800 W: 42 ft/s.

What box do two Sky High Car Audio FMX-8 D1 subs need?

Two subs need twice the volume: 0.71 ft³ sealed, or 0.92 ft³ ported at the same 41 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.