Ascendant Audio SMD Signature 18 D1

18″ subwoofer · dual 1 Ω · 3,500 W RMS

29.7 HzFs, resonance

0.30Qts

4.04 ft³Vas

1.26″Xmax

3,500 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, 3,500 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

2.95 ft³ (83.5 L)

Net volume

Bass character (Qtc)	Dry and tight · 0.47
Fc	46 Hz
F3 (−3 dB, no cabin gain)	80 Hz
Example box (outside)	20 1/16″ × 20 1/16″ × 17 7/16″

Open sealed box in designer

Ported

deeper, louder

5.54 ft³ (157 L)

Net volume

Tuning (Fb)	33 Hz
Port	slot 5 7/8 × 19 7/16″, 42″ long
Port velocity at 3,500 W	71 ft/s
F3 (−3 dB, no cabin gain)	30 Hz
Example box (outside)	31 1/2″ × 20 7/8″ × 27 9/16″

Open ported box in designer

Deeper: 3.60 ft³ (102 L) tuned to 32 Hz, 31 1/2″ × 20 7/8″ × 23 1/8″ 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	18″
Voice coils	dual 1 Ω
RMS power	3,500 W
Fs	29.7 Hz
Qts	0.30
Qes	0.32
Qms	5.45
Vas	4.04 ft³

Re (one coil)	0.7 Ω
Sd	187.6 in²
Xmax	1.26″
Vd	236.3 in³ calc.
Mms	521 g calc.
BL	14.6 T·m calc.
EBP	93 — sealed or ported calc.
Sensitivity, 1 W / 1 m	91.7 dB calc.

Mounting dimensions

Cutout diameter	16 3/4″
Mounting depth	15″
Overall diameter	18 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/20100417121144/http://www.ascendantaudio.com:80/smd.php

Other Ascendant Audio 18″ models

Ascendant Audio Havoc 18 D1 18″ · dual 1 Ω
Ascendant Audio Havoc 18 D2 18″ · dual 2 Ω
Ascendant Audio Mayhem 18 D1 18″ · dual 1 Ω
Ascendant Audio Mayhem 18 D2 18″ · dual 2 Ω
Ascendant Audio SMD Signature 18 D2 18″ · dual 2 Ω
Ascendant Audio SMD V2 18 D1 18″ · dual 1 Ω
Ascendant Audio SMD V2 18 D2 18″ · dual 2 Ω
Ascendant Audio TEAM 18 D1 18″ · dual 1 Ω
Ascendant Audio TEAM 18 D2 18″ · dual 2 Ω

Similar 18″ subwoofers from other brands

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

Fi Audio NEO 3.9 18 D2 2.38 ft³ sealed · 5.54 ft³ ported
Sundown Audio SAv2-18 D2 1.87 ft³ sealed · 4.52 ft³ ported
Fi Audio NEO 3.9 18 D1 2.38 ft³ sealed · 5.54 ft³ ported
Fi Audio SP3 Plus 18 D1 2.38 ft³ sealed · 5.54 ft³ ported
Fi Audio SP3 Plus 18 D2 2.38 ft³ sealed · 5.54 ft³ ported
Sundown Audio NSv4-18 D2 2.86 ft³ sealed · 5.23 ft³ ported

FAQ

What box does the Ascendant Audio SMD Signature 18 D1 need?

Recommended net volume: 2.95 ft³ sealed, 5.54 ft³ ported tuned to 33 Hz — for one sub in a sedan at 3,500 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.

What are the Ascendant Audio SMD Signature 18 D1 Thiele/Small specs?

Fs 29.7 Hz, Qts 0.30, Vas 4.04 ft³, Xmax 1.26″, Sd 187.6 in².

What is the Ascendant Audio SMD Signature 18 D1 mounting depth?

Mounting depth is 15″, cutout diameter 16 3/4″. The inside depth of the box must exceed the mounting depth by at least 1″.

How much power does the Ascendant Audio SMD Signature 18 D1 handle and how do I wire it?

RMS power rating: 3,500 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.