Fi Audio IB312 S4

12″ subwoofer · 4 Ω · 550 W RMS

23.6 HzFs, resonance

0.55Qts

2.95 ft³Vas

1.18″Xmax

550 WRMS

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

1.70 ft³ (48 L)

Net volume

Bass character (Qtc)	Tight and punchy · 0.91
Fc	39 Hz
F3 (−3 dB, no cabin gain)	34 Hz
Example box (outside)	14 3/16″ × 14 3/16″ × 20 9/16″

Open sealed box in designer

Ported

deeper, louder

2.19 ft³ (62 L)

Net volume

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″

Open ported box in designer

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

Where to buy Amazon

Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Size	12″
Voice coils	4 Ω
RMS power	550 W
Fs	23.6 Hz
Qts	0.55
Qes	0.64
Qms	4
Vas	2.95 ft³

Re	2.8 Ω
Sd	74.4 in²
Xmax	1.18″
Vd	87.9 in³ calc.
Mms	178 g calc.
BL	10.7 T·m calc.
EBP	37 — suits sealed calc.
Sensitivity, 1 W / 1 m	84.3 dB calc.

Mounting dimensions

Cutout diameter	11 1/8″
Mounting depth	6 1/2″
Overall diameter	12 1/2″

“≈” 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

web.archive.org/web/20110712231407/http://www.ficaraudio.com:80/sess/utn;jsessio

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
Ground Zero GZRW 12FL (2x2 Ohm) 1.73 ft³ sealed · 2.12 ft³ ported
Infinity Reference 1200S 1.77 ft³ sealed · 2.30 ft³ ported
JBL Club WS1200 (4 ohm) 1.77 ft³ sealed · 2.30 ft³ ported
JBL Club WS1200 (SSI set to 4 ohm) 1.77 ft³ sealed · 2.30 ft³ ported
Audio System R 12 FLAT 1.80 ft³ sealed · 2.30 ft³ ported

FAQ

What box does the Fi Audio IB312 S4 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 S4 Thiele/Small specs?

Fs 23.6 Hz, Qts 0.55, Vas 2.95 ft³, Xmax 1.18″, Sd 74.4 in².

What is the Fi Audio IB312 S4 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 S4 handle and how do I wire it?

RMS power rating: 550 W. Wiring for several subs and amp power — in the wiring calculator.