Sky High Car Audio FEX-15 D4
15″ subwoofer · dual 4 Ω · 1,250 W RMS
The Sky High Car Audio FEX-15 D4 is a 15″ subwoofer. With Qts 0.64 and EBP 43 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, 1,250 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 · 0.96 |
|---|---|
| Fc | 46 Hz |
| F3 (−3 dB, no cabin gain) | 39 Hz |
| Example box (outside) | 31 1/2″ × 17 11/16″ × 12 3/8″ |
Ported
deeper, louder| Tuning (Fb) | 33 Hz |
|---|---|
| Port | slot 2 9/16 × 16 5/16″, 28 3/8″ long |
| Port velocity at 1,250 W | 61 ft/s |
| F3 (−3 dB, no cabin gain) | 32 Hz |
| Example box (outside) | 31 1/2″ × 17 11/16″ × 15 11/16″ |
Deeper: 4.98 ft³ (141 L) tuned to 33 Hz, 31 1/2″ × 17 11/16″ × 22 7/8″ 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 | 15″ |
|---|---|
| Voice coils | dual 4 Ω |
| RMS power | 1,250 W |
| Fs | 30.4 Hz |
| Qts | 0.64 |
| Qes | 0.709 |
| Qms | 6.19 |
| Vas | 3.79 ft³ |
| Re (one coil) | 3.3 Ω |
|---|---|
| Sd | 128.6 in² |
| Xmax | 0.75″ |
| Vd | 96.2 in³ calc. |
| Mms | 249 g calc. |
| BL | 14.9 T·m calc. |
| EBP | 43 — suits sealed calc. |
| Sensitivity, 1 W / 1 m | 88.3 dB calc. |
Mounting dimensions
| Cutout diameter | 13 9/16″ |
|---|---|
| Mounting depth | 8 3/8″ |
| Overall diameter | 15 3/8″ |
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.
- Excursion — behind the third row sealed and ported box
“≈” 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 FEX-15 D2 | dual 2 Ω | 2.09 Ω | 0.873 | 3.81 ft³ | 2.93 ft³ | 3.04 ft³ · 33 Hz |
| Sky High Car Audio FEX-15 D4 | dual 4 Ω | 3.3 Ω | 0.709 | 3.79 ft³ | 2.93 ft³ | 3.04 ft³ · 33 Hz |
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 FMX-15 D1 15″ · dual 1 Ω
- Sky High Car Audio FMX-15 D2 15″ · dual 2 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.
- Soundstream PCW-15 2.83 ft³ sealed · 2.86 ft³ ported
- Rockville W15K6D2 V2 3.00 ft³ sealed · 3.39 ft³ ported
- NVX VCW152v3 2.83 ft³ sealed · 2.97 ft³ ported
- Diamond CM315D2 2.79 ft³ sealed · 2.44 ft³ ported
- MD.Lab SW-A15 2.86 ft³ sealed · 2.86 ft³ ported
- Audiobahn DUB500 2.72 ft³ sealed · 2.44 ft³ ported
FAQ
What box does the Sky High Car Audio FEX-15 D4 need?
Recommended net volume: 2.93 ft³ sealed, 3.04 ft³ ported tuned to 33 Hz — for one sub in a sedan at 1,250 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 FEX-15 D4 Thiele/Small specs?
Fs 30.4 Hz, Qts 0.64, Vas 3.79 ft³, Xmax 0.75″, Sd 128.6 in².
What is the Sky High Car Audio FEX-15 D4 mounting depth?
Mounting depth is 8 3/8″, cutout diameter 13 9/16″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Sky High Car Audio FEX-15 D4 handle and how do I wire it?
RMS power rating: 1,250 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.
Is the Sky High Car Audio FEX-15 D4 better sealed or ported?
EBP 43: a sealed box (2.93 ft³) suits it best — tight bass in a compact enclosure. Ported is possible (3.04 ft³, tuned to 33 Hz) but larger.
What port does the Sky High Car Audio FEX-15 D4 need?
For the 3.04 ft³ ported box tuned to 33 Hz: slot 2 9/16 × 16 5/16″, 28 3/8″ long, area 41.7 in²; or a round port Ø7 5/16″, ≈ 28 3/8″ long. Port air speed at 1,250 W: 61 ft/s.
What box do two Sky High Car Audio FEX-15 D4 subs need?
Two subs need twice the volume: 5.86 ft³ sealed, or 6.07 ft³ ported at the same 33 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.