Sky High Car Audio FXXL-18 D1
18″ subwoofer · dual 1 Ω · 5,000 W RMS
| 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 |
- Fs, Vas and Sd don't match the moving mass of 526.1 g (they give 660 g) — one of the spec sheet values is probably wrong.
Recommended box
For a sedan, one sub, 5,000 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| Bass character (Qtc) | Tight and punchy · 0.86 |
|---|---|
| Fc | 36 Hz |
| F3 (−3 dB, no cabin gain) | 32 Hz |
| Example box (outside) | 19 11/16″ × 19 11/16″ × 23 3/4″ |
Ported
deeper, louder| Tuning (Fb) | 30 Hz |
|---|---|
| Port | slot 3 1/8 × 19 1/16″, 54 7/16″ long |
| Port velocity at 5,000 W | 79 ft/s |
| F3 (−3 dB, no cabin gain) | 28 Hz |
| Example box (outside) | 28 11/16″ × 20 1/2″ × 19 1/2″ |
Deeper: 6.85 ft³ (194 L) tuned to 25 Hz, 31 1/2″ × 20 1/2″ × 24 3/16″ outside — a bigger box with flatter deep bass. Open in the calculator
Projects with this subwoofer
Boxes that users designed and published: plans, cut sheet and response graph.
Thiele/Small parameters
| Size | 18″ |
|---|---|
| Voice coils | dual 1 Ω |
| RMS power | 5,000 W |
| Fs | 26.1 Hz |
| Qts | 0.62 |
| Qes | 0.714 |
| Qms | 4.74 |
| Vas | 3.67 ft³ |
| Re (one coil) | 0.66 Ω |
|---|---|
| Sd | 176.7 in² |
| Xmax | 1.42″ |
| Vd | 250.5 in³ calc. |
| Mms | 660 g calc. |
| BL | 10 T·m calc. |
| EBP | 37 — suits sealed calc. |
| Sensitivity, 1 W / 1 m | 86.1 dB calc. |
Mounting dimensions
| Cutout diameter | 16 5/8″ |
|---|---|
| Mounting depth | 12 3/16″ |
| Overall diameter | 18 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
Other Sky High Car Audio 18″ models
- Sky High Car Audio BMX-18 D1 18″ · dual 1 Ω
- Sky High Car Audio BMX-18 D2 18″ · dual 2 Ω
- Sky High Car Audio FEX-18 D2 18″ · dual 2 Ω
- Sky High Car Audio FEX-18 D4 18″ · dual 4 Ω
- Sky High Car Audio FMX-18 D1 18″ · dual 1 Ω
- Sky High Car Audio FMX-18 D2 18″ · dual 2 Ω
- Sky High Car Audio FXB-18 D2 18″ · dual 2 Ω
- Sky High Car Audio FXB-18 D4 18″ · dual 4 Ω
- Sky High Car Audio FXXL-18 D2 18″ · dual 2 Ω
Similar 18″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Sundown Audio M18 D2 4.17 ft³ sealed · 3.32 ft³ ported
- Sundown Audio M18 D1 4.17 ft³ sealed · 3.18 ft³ ported
- Kicker Solo-Baric L7X 18" 2-Ohm DVC (49L7X182) 4.98 ft³ sealed · 7.52 ft³ ported
- Sundown Audio Xv4-18 D1 2.90 ft³ sealed · 6.99 ft³ ported
- Sundown Audio Xv3-18 D2 3.28 ft³ sealed · 6.99 ft³ ported
- Kicker Solo-Baric L7X 18" 1-Ohm DVC (49L7X181) 4.20 ft³ sealed · 7.52 ft³ ported
FAQ
What box does the Sky High Car Audio FXXL-18 D1 need?
Recommended net volume: 4.03 ft³ sealed, 2.93 ft³ ported tuned to 30 Hz — for one sub in a sedan at 5,000 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 FXXL-18 D1 Thiele/Small specs?
Fs 26.1 Hz, Qts 0.62, Vas 3.67 ft³, Xmax 1.42″, Sd 176.7 in².
What is the Sky High Car Audio FXXL-18 D1 mounting depth?
Mounting depth is 12 3/16″, cutout diameter 16 5/8″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Sky High Car Audio FXXL-18 D1 handle and how do I wire it?
RMS power rating: 5,000 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.