Fi Audio SP3 Plus 15 D2
15″ subwoofer · dual 2 Ω · 2,500 W RMS
The Fi Audio SP3 Plus 15 D2 is a 15″ subwoofer. With Qts 0.25 and EBP 125 it suits a ported box: deeper and louder; sealed, the bass sounds a bit dry. Long excursion (Xmax 1.34″) — built for loud music and high power.
| Source | web.archive.org · 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, 2,500 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) | Dry and tight · 0.39 |
|---|---|
| Fc | 51 Hz |
| F3 (−3 dB, no cabin gain) | 112 Hz |
| Example box (outside) | 17 5/16″ × 17 5/16″ × 13 1/2″ |
Ported
deeper, louder| Tuning (Fb) | 34 Hz |
|---|---|
| Port | slot 5 1/2 × 16 11/16″, 49 7/16″ long |
| Port velocity at 2,500 W | 64 ft/s |
| F3 (−3 dB, no cabin gain) | 90 Hz |
| Example box (outside) | 31 1/2″ × 18 1/8″ × 24 9/16″ |
Deeper: 2.40 ft³ (68 L) tuned to 32 Hz, 31 1/2″ × 18 1/8″ × 16 9/16″ 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 | 15″ |
|---|---|
| Voice coils | dual 2 Ω |
| RMS power | 2,500 W |
| Fs | 32.4 Hz |
| Qts | 0.25 |
| Qes | 0.26 |
| Qms | 6.65 |
| Vas | 2.29 ft³ |
| Re (one coil) | 1.8 Ω |
|---|---|
| Sd | 125.6 in² |
| Xmax | 1.34″ |
| Vd | 168.1 in³ calc. |
| Mms | 346 g calc. |
| BL | 22.1 T·m calc. |
| EBP | 125 — suits ported calc. |
| Sensitivity, 1 W / 1 m | 91.3 dB calc. |
Mounting dimensions
| Cutout diameter | 14 1/8″ |
|---|---|
| Mounting depth | 11″ |
| Overall diameter | 15 5/8″ |
“≈” 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 |
|---|---|---|---|---|---|---|
| Fi Audio SP3 Plus 15 D1 | dual 1 Ω | 0.9 Ω | 0.26 | 2.29 ft³ | 1.59 ft³ | 3.71 ft³ · 34 Hz |
| Fi Audio SP3 Plus 15 D2 | dual 2 Ω | 1.8 Ω | 0.26 | 2.29 ft³ | 1.59 ft³ | 3.71 ft³ · 34 Hz |
Other Fi Audio 15″ models
- Fi Audio Alpha v1 15 S1 15″ · 1 Ω
- Fi Audio Alpha v1 15 S2 15″ · 2 Ω
- Fi Audio Alpha v1 15 S4 15″ · 4 Ω
- Fi Audio Alpha v2 15 S2 15″ · 2 Ω
- Fi Audio Alpha v2 15 S4 15″ · 4 Ω
- Fi Audio BL-NEO 15 D1 15″ · dual 1 Ω
- Fi Audio BL-NEO 15 D2 15″ · dual 2 Ω
- Fi Audio BL15 D1 15″ · dual 1 Ω
- Fi Audio BL15 D2 15″ · dual 2 Ω
- Fi Audio BL15v3 D1 15″ · dual 1 Ω
- Fi Audio BL15v3 D2 15″ · dual 2 Ω
- Fi Audio BL15v3.1 D1 15″ · dual 1 Ω
Similar 15″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Resilient Sounds Platinum 15 D1 1.36 ft³ sealed · 3.57 ft³ ported
- Deaf Bonce Apocalypse DB-4515R D1 1.73 ft³ sealed · 3.67 ft³ ported
- Edge EDS15D1-E7 1.06 ft³ sealed · 3.46 ft³ ported
- Ascendant Audio SMD Signature 15 D2 2.07 ft³ sealed · 3.71 ft³ ported
- Deaf Bonce Apocalypse DB-4515R D2 1.73 ft³ sealed · 3.67 ft³ ported
- Ascendant Audio SMD Signature 15 D1 2.07 ft³ sealed · 3.71 ft³ ported
FAQ
What box does the Fi Audio SP3 Plus 15 D2 need?
Recommended net volume: 1.59 ft³ sealed, 3.71 ft³ ported tuned to 34 Hz — for one sub in a sedan at 2,500 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.
What are the Fi Audio SP3 Plus 15 D2 Thiele/Small specs?
Fs 32.4 Hz, Qts 0.25, Vas 2.29 ft³, Xmax 1.34″, Sd 125.6 in².
What is the Fi Audio SP3 Plus 15 D2 mounting depth?
Mounting depth is 11″, cutout diameter 14 1/8″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Fi Audio SP3 Plus 15 D2 handle and how do I wire it?
RMS power rating: 2,500 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 Fi Audio SP3 Plus 15 D2 better sealed or ported?
EBP 125: a ported box (3.71 ft³, tuned to 34 Hz) suits it best — deeper and louder. Sealed (1.59 ft³) the bass is drier.
What port does the Fi Audio SP3 Plus 15 D2 need?
For the 3.71 ft³ ported box tuned to 34 Hz: slot 5 1/2 × 16 11/16″, 49 7/16″ long, area 92 in²; or a round port Ø10 13/16″, ≈ 49 7/16″ long. Port air speed at 2,500 W: 64 ft/s.
What box do two Fi Audio SP3 Plus 15 D2 subs need?
Two subs need twice the volume: 3.18 ft³ sealed, or 7.42 ft³ ported at the same 34 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.