Fi Audio SP3 Plus 15 D1

15″ subwoofer · dual 1 Ω · 2,500 W RMS

32.4 HzFs, resonance

0.25Qts

2.29 ft³Vas

1.34″Xmax

2,500 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, 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

1.59 ft³ (45 L)

Net volume

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″

Open sealed box in designer

Ported

deeper, louder

3.71 ft³ (105 L)

Net volume

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″

Open ported box in designer

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

Where to buy Amazon

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

Thiele/Small parameters

Size	15″
Voice coils	dual 1 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)	0.9 Ω
Sd	125.6 in²
Xmax	1.34″
Vd	168.1 in³ calc.
Mms	346 g calc.
BL	15.6 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

web.archive.org/web/20191122074724/https://ficaraudio.com/product/sp3-plus-serie

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 D1 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 D1 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 D1 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 D1 handle and how do I wire it?

RMS power rating: 2,500 W. Dual 1 Ω voice coils: series gives 2 Ω, parallel gives 0.5 Ω at the amp. Wiring for several subs and amp power — in the wiring calculator.