Fi Audio X10 S4

10″ subwoofer · 4 Ω · 400 W RMS

36.4 HzFs, resonance

0.41Qts

0.78 ft³Vas

0.71″Xmax

400 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, 400 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

0.42 ft³ (12 L)

Net volume

Bass character (Qtc)	Flat and accurate · 0.68
Fc	61 Hz
F3 (−3 dB, no cabin gain)	67 Hz
Example box (outside)	12 5/8″ × 12 5/8″ × 8 1/8″

Open sealed box in designer

Ported

deeper, louder

0.78 ft³ (22 L)

Net volume

Tuning (Fb)	43 Hz
Port	2 round ports Ø2 1/2″, 16 11/16″ long
Port velocity at 400 W	105 ft/s
F3 (−3 dB, no cabin gain)	40 Hz
Example box (outside)	18 9/16″ × 15 3/4″ × 8 1/4″

At 400 W this example’s port will be noisy: air speed 105 ft/s, while the limit is 82 ft/s. It stays quiet up to about 240 W. Full power needs a port of at least 12.8 in², which means a bigger box than this example — size it in the designer.

Open ported box in designer

Deeper: 0.92 ft³ (26 L) tuned to 37 Hz, 16 5/8″ × 15 3/4″ × 13″ 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	10″
Voice coils	4 Ω
RMS power	400 W
Fs	36.4 Hz
Qts	0.41
Qes	0.44
Qms	5.16
Vas	0.78 ft³

Re	2.9 Ω
Sd	48.1 in²
Xmax	0.71″
Vd	34.1 in³ calc.
Mms	118 g calc.
BL	13.3 T·m calc.
EBP	83 — sealed or ported calc.
Sensitivity, 1 W / 1 m	85.8 dB calc.

Mounting dimensions

Cutout diameter	9 1/4″
Mounting depth	5 3/4″
Overall diameter	11″

“≈” 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/20110712231226/http://www.ficaraudio.com:80/sess/utn;jsessio

Other Fi Audio 10″ models

Fi Audio Alpha v1 10 S1 10″ · 1 Ω
Fi Audio Alpha v1 10 S2 10″ · 2 Ω
Fi Audio Alpha v1 10 S4 10″ · 4 Ω
Fi Audio Alpha v2 10 S2 10″ · 2 Ω
Fi Audio Alpha v2 10 S4 10″ · 4 Ω
Fi Audio Alpha v2.1 10 S2 10″ · 2 Ω
Fi Audio Alpha v2.1 10 S4 10″ · 4 Ω
Fi Audio BL-NEO 10 D1 10″ · dual 1 Ω
Fi Audio BL-NEO 10 D2 10″ · dual 2 Ω
Fi Audio BL10 D1 10″ · dual 1 Ω
Fi Audio BL10 D2 10″ · dual 2 Ω
Fi Audio BL10v3 D1 10″ · dual 1 Ω

Similar 10″ subwoofers from other brands

Close in Fs, Qts and Vas — a box of similar volume will suit them.

Elemental Designs E10a 0.46 ft³ sealed · 0.81 ft³ ported
Kicker CompVX 10" 2-Ohm DVC (50CVX102) 0.49 ft³ sealed · 1.66 ft³ ported
PowerBass 3XL-101D 0.53 ft³ sealed · 1.66 ft³ ported
AMP MASS 500 10D2 V.2 0.46 ft³ sealed · 0.81 ft³ ported
Helix IQ W10-DVC2 (2x2 Ohm) 0.53 ft³ sealed · 0.88 ft³ ported
Dayton Audio SS10-22 0.53 ft³ sealed · 0.85 ft³ ported

FAQ

What box does the Fi Audio X10 S4 need?

Recommended net volume: 0.42 ft³ sealed, 0.78 ft³ ported tuned to 43 Hz — for one sub in a sedan at 400 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.

What are the Fi Audio X10 S4 Thiele/Small specs?

Fs 36.4 Hz, Qts 0.41, Vas 0.78 ft³, Xmax 0.71″, Sd 48.1 in².

What is the Fi Audio X10 S4 mounting depth?

Mounting depth is 5 3/4″, cutout diameter 9 1/4″. The inside depth of the box must exceed the mounting depth by at least 1″.

How much power does the Fi Audio X10 S4 handle and how do I wire it?

RMS power rating: 400 W. Wiring for several subs and amp power — in the wiring calculator.