Sky High Car Audio FXB-18 D2
18″ subwoofer · dual 2 Ω · 1,500 W RMS
The Sky High Car Audio FXB-18 D2 is a 18″ subwoofer. With Qts 0.66 and EBP 35 it suits a sealed box: tight bass in a small enclosure; a ported box would need a lot of volume.
| 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| Bass character (Qtc) | Boomy, with a bump · 0.97 |
|---|---|
| Fc | 38 Hz |
| F3 (−3 dB, no cabin gain) | 32 Hz |
| Example box (outside) | 31 1/2″ × 20 1/2″ × 15 1/8″ |
Ported
deeper, louder| Tuning (Fb) | 30 Hz |
|---|---|
| Port | slot 2 9/16 × 19 1/16″, 31 7/8″ long |
| Port velocity at 1,500 W | 61 ft/s |
| F3 (−3 dB, no cabin gain) | 28 Hz |
| Example box (outside) | 31 1/2″ × 20 1/2″ × 17 3/16″ |
Deeper: 7.24 ft³ (205 L) tuned to 28 Hz, 31 1/2″ × 20 1/2″ × 28 1/4″ 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 2 Ω |
| RMS power | 1,500 W |
| Fs | 26.1 Hz |
| Qts | 0.66 |
| Qes | 0.74 |
| Qms | 6.56 |
| Vas | 4.80 ft³ |
| Re (one coil) | 1.9 Ω |
|---|---|
| Sd | 187.2 in² |
| Xmax | 1.18″ |
| Vd | 221.2 in³ calc. |
| Mms | 565 g calc. |
| BL | 15.4 T·m calc. |
| EBP | 35 — suits sealed calc. |
| Sensitivity, 1 W / 1 m | 87.1 dB calc. |
Mounting dimensions
| Cutout diameter | 16 5/8″ |
|---|---|
| Mounting depth | 10 3/8″ |
| Overall diameter | 18 1/2″ |
Cone area (Sd) calculated from Fs, Vas and Mms: 187.2 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
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 FXB-18 D2 | dual 2 Ω | 1.9 Ω | 0.74 | 4.80 ft³ | 4.27 ft³ | 3.85 ft³ · 30 Hz |
| Sky High Car Audio FXB-18 D4 | dual 4 Ω | 3.2 Ω | 0.94 | 4.69 ft³ | 4.31 ft³ | 3.74 ft³ · 30 Hz |
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 FXXL-18 D1 18″ · dual 1 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.
- Dayton Audio UM18-22 4.31 ft³ sealed · 4.10 ft³ ported
- Sundown Audio M18 D2 4.17 ft³ sealed · 3.32 ft³ ported
- Sundown Audio M18 D1 4.17 ft³ sealed · 3.18 ft³ ported
- DL Audio Phoenix Bass Machine 18 (2+2) 4.13 ft³ sealed · 4.31 ft³ ported
- URAL Bulava 18 (2+2) 4.20 ft³ sealed · 4.66 ft³ ported
- DC Audio Level 4 M3 18 D1 4.31 ft³ sealed · 4.94 ft³ ported
FAQ
What box does the Sky High Car Audio FXB-18 D2 need?
Recommended net volume: 4.27 ft³ sealed, 3.85 ft³ ported tuned to 30 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-18 D2 Thiele/Small specs?
Fs 26.1 Hz, Qts 0.66, Vas 4.80 ft³, Xmax 1.18″, Sd 187.2 in².
What is the Sky High Car Audio FXB-18 D2 mounting depth?
Mounting depth is 10 3/8″, 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 FXB-18 D2 handle and how do I wire it?
RMS power rating: 1,500 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.
Is the Sky High Car Audio FXB-18 D2 better sealed or ported?
EBP 35: a sealed box (4.27 ft³) suits it best — tight bass in a compact enclosure. Ported is possible (3.85 ft³, tuned to 30 Hz) but larger.
What port does the Sky High Car Audio FXB-18 D2 need?
For the 3.85 ft³ ported box tuned to 30 Hz: slot 2 9/16 × 19 1/16″, 31 7/8″ long, area 48.8 in²; or a round port Ø7 7/8″, ≈ 31 7/8″ long. Port air speed at 1,500 W: 61 ft/s.
What box do two Sky High Car Audio FXB-18 D2 subs need?
Two subs need twice the volume: 8.55 ft³ sealed, or 7.70 ft³ ported at the same 30 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.