Fi Audio IB312 S2
12″ subwoofer · 2 Ω · 550 W RMS
The Fi Audio IB312 S2 is a 12″ subwoofer. With Qts 0.58 and EBP 35 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 · 0.95 |
|---|---|
| Fc | 39 Hz |
| F3 (−3 dB, no cabin gain) | 33 Hz |
| Example box (outside) | 14 3/16″ × 14 3/16″ × 20 9/16″ |
Ported
deeper, louder| Tuning (Fb) | 30 Hz |
|---|---|
| Port | slot 1 9/16 × 14 5/16″, 26 11/16″ long |
| Port velocity at 550 W | 63 ft/s |
| F3 (−3 dB, no cabin gain) | 28 Hz |
| Example box (outside) | 31 1/2″ × 15 3/4″ × 12 9/16″ |
Deeper: 2.90 ft³ (82 L) tuned to 29 Hz, 31 1/2″ × 15 3/4″ × 15 11/16″ 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 | 12″ |
|---|---|
| Voice coils | 2 Ω |
| RMS power | 550 W |
| Fs | 23.6 Hz |
| Qts | 0.58 |
| Qes | 0.67 |
| Qms | 4.06 |
| Vas | 2.94 ft³ |
| Re | 1.5 Ω |
|---|---|
| Sd | 74.4 in² |
| Xmax | 1.18″ |
| Vd | 87.9 in³ calc. |
| Mms | 178 g calc. |
| BL | 7.7 T·m calc. |
| EBP | 35 — suits sealed calc. |
| Sensitivity, 1 W / 1 m | 84.1 dB calc. |
Mounting dimensions
| Cutout diameter | 11 1/8″ |
|---|---|
| Mounting depth | 6 1/2″ |
| Overall diameter | 12 1/2″ |
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.
- Bronco 4-door — behind the rear seat sealed and ported box
- Wrangler 4-door, hard top — behind the rear seat sealed and ported box
- Wrangler 4-door, soft top — behind the rear seat sealed and ported box
- Silverado / Sierra Crew Cab — under the rear seat sealed and ported box
- FJ Cruiser — behind the rear seat sealed and ported box
- El Camino 1978–87 — behind the seat sealed and ported box
- Cherokee XJ — cargo area, spare moved out sealed and ported box
- Excursion — behind the third row sealed and ported box
- Mustang 2015–2023 coupe — trunk sealed and ported box
- Challenger / Charger — trunk sealed and ported box
- Club Car Precedent — under the rear seat sealed 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 |
|---|---|---|---|---|---|---|
| Fi Audio IB312 S2 | 2 Ω | 1.5 Ω | 0.67 | 2.94 ft³ | 1.70 ft³ | 2.19 ft³ · 30 Hz |
| Fi Audio IB312 S4 | 4 Ω | 2.8 Ω | 0.64 | 2.95 ft³ | 1.70 ft³ | 2.19 ft³ · 30 Hz |
Other Fi Audio 12″ models
- Fi Audio Alpha 12 S2 12″ · 2 Ω
- Fi Audio Alpha 12 S4 12″ · 4 Ω
- Fi Audio Alpha v1 12 S1 12″ · 1 Ω
- Fi Audio Alpha v1 12 S2 12″ · 2 Ω
- Fi Audio Alpha v1 12 S4 12″ · 4 Ω
- Fi Audio Alpha v2 12 S2 12″ · 2 Ω
- Fi Audio Alpha v2 12 S4 12″ · 4 Ω
- Fi Audio Alpha v2.1 12 S2 12″ · 2 Ω
- Fi Audio Alpha v2.1 12 S4 12″ · 4 Ω
- Fi Audio BL-NEO 12 D1 12″ · dual 1 Ω
- Fi Audio BL-NEO 12 D2 12″ · dual 2 Ω
- Fi Audio BL12 D1 12″ · dual 1 Ω
Similar 12″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Focal SUB 12 DUAL (DVC 4+4 ohm) 1.66 ft³ sealed · 2.15 ft³ ported
- Audio System R 12 FLAT 1.80 ft³ sealed · 2.30 ft³ ported
- AMPIRE FLAT12 1.80 ft³ sealed · 2.22 ft³ ported
- Polk Audio dX12-4 1.80 ft³ sealed · 2.22 ft³ ported
- Hifonics BRZ12SQD4 (Brutus SQ 12" DVC 4ohm) 2.40 ft³ sealed · 2.75 ft³ ported
- Ground Zero GZRW 12FL (2x2 Ohm) 1.73 ft³ sealed · 2.12 ft³ ported
FAQ
What box does the Fi Audio IB312 S2 need?
Recommended net volume: 1.70 ft³ sealed, 2.19 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 IB312 S2 Thiele/Small specs?
Fs 23.6 Hz, Qts 0.58, Vas 2.94 ft³, Xmax 1.18″, Sd 74.4 in².
What is the Fi Audio IB312 S2 mounting depth?
Mounting depth is 6 1/2″, cutout diameter 11 1/8″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Fi Audio IB312 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 IB312 S2 better sealed or ported?
EBP 35: a sealed box (1.70 ft³) suits it best — tight bass in a compact enclosure. Ported is possible (2.19 ft³, tuned to 30 Hz) but larger.
What port does the Fi Audio IB312 S2 need?
For the 2.19 ft³ ported box tuned to 30 Hz: slot 1 9/16 × 14 5/16″, 26 11/16″ long, area 22.6 in²; or a round port Ø5 3/8″, ≈ 26 11/16″ long. Port air speed at 550 W: 63 ft/s.
What box do two Fi Audio IB312 S2 subs need?
Two subs need twice the volume: 3.39 ft³ sealed, or 4.38 ft³ ported at the same 30 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.