Fi Audio IB315 S2
15″ subwoofer · 2 Ω · 550 W RMS
The Fi Audio IB315 S2 is a 15″ subwoofer. With Qts 0.63 and EBP 31 it suits a sealed box: tight bass in a small enclosure; a ported box would need a lot of volume. Long excursion (Xmax 1.18″) — 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, 550 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 · 1.14 |
|---|---|
| Fc | 41 Hz |
| F3 (−3 dB, no cabin gain) | 32 Hz |
| Example box (outside) | 31 1/2″ × 18 1/8″ × 11 7/8″ |
Ported
deeper, louder| Tuning (Fb) | 30 Hz |
|---|---|
| Port | slot 1 9/16 × 16 11/16″, 16 13/16″ long |
| Port velocity at 550 W | 62 ft/s |
| F3 (−3 dB, no cabin gain) | 29 Hz |
| Example box (outside) | 31 1/2″ × 18 1/8″ × 15 15/16″ |
Deeper: 4.87 ft³ (138 L) tuned to 31 Hz, 31 1/2″ × 18 1/8″ × 20″ 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 | 2 Ω |
| RMS power | 550 W |
| Fs | 22.7 Hz |
| Qts | 0.63 |
| Qes | 0.74 |
| Qms | 4.3 |
| Vas | 6.47 ft³ |
| Re | 1.5 Ω |
|---|---|
| Sd | 125.6 in² |
| Xmax | 1.18″ |
| Vd | 148.3 in³ calc. |
| Mms | 249 g calc. |
| BL | 8.5 T·m calc. |
| EBP | 31 — suits sealed calc. |
| Sensitivity, 1 W / 1 m | 86.6 dB calc. |
Mounting dimensions
| Cutout diameter | 14 1/8″ |
|---|---|
| Mounting depth | 8″ |
| 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 IB315 S2 | 2 Ω | 1.5 Ω | 0.74 | 6.47 ft³ | 2.86 ft³ | 3.71 ft³ · 30 Hz |
| Fi Audio IB315 S4 | 4 Ω | 2.8 Ω | 0.7 | 6.47 ft³ | 2.86 ft³ | 3.71 ft³ · 30 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.
- Kicker Solo-Baric L7R 15" 4-Ohm DVC (45L7R154) 3.71 ft³ sealed · 4.52 ft³ ported
- Rockford Fosgate Punch P115S4 (Stage-1, 2004) 3.04 ft³ sealed · 3.96 ft³ ported
- Rockford Fosgate Punch HE2 RFP4115 2.86 ft³ sealed · 3.71 ft³ ported
- Cerwin-Vega Mobile V154DV2 (Vega 15" DVC 4ohm) 2.83 ft³ sealed · 3.00 ft³ ported
- Diamond D315D4 3.07 ft³ sealed · 3.99 ft³ ported
- Treo TS15.8 2.58 ft³ sealed · 3.35 ft³ ported
FAQ
What box does the Fi Audio IB315 S2 need?
Recommended net volume: 2.86 ft³ sealed, 3.71 ft³ ported tuned to 30 Hz — for one sub in a sedan at 550 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.
What are the Fi Audio IB315 S2 Thiele/Small specs?
Fs 22.7 Hz, Qts 0.63, Vas 6.47 ft³, Xmax 1.18″, Sd 125.6 in².
What is the Fi Audio IB315 S2 mounting depth?
Mounting depth is 8″, 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 IB315 S2 handle and how do I wire it?
RMS power rating: 550 W. Wiring for several subs and amp power — in the wiring calculator.
Is the Fi Audio IB315 S2 better sealed or ported?
EBP 31: a sealed box (2.86 ft³) suits it best — tight bass in a compact enclosure. Ported is possible (3.71 ft³, tuned to 30 Hz) but larger.
What port does the Fi Audio IB315 S2 need?
For the 3.71 ft³ ported box tuned to 30 Hz: slot 1 9/16 × 16 11/16″, 16 13/16″ long, area 26.3 in²; or a round port Ø5 13/16″, ≈ 16 13/16″ long. Port air speed at 550 W: 62 ft/s.
What box do two Fi Audio IB315 S2 subs need?
Two subs need twice the volume: 5.72 ft³ sealed, or 7.42 ft³ ported at the same 30 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.