Sundown Audio Xv4-18 D2

18″ subwoofer · dual 2 Ω · 2,750 W RMS

Fs 25.6 HzQts 0.48Vas 0.62 ft³Xmax 1.18″
The published specs don’t add up:

Recommended box

For a sedan, one sub, 2,750 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

Net volume2.81 ft³ (79.5 L)
Qtc0.53
Fc28 Hz
F3 (−3 dB, no cabin gain)41 Hz
Example box (outside)19 11/16″ × 19 11/16″ × 17 7/16″
Open sealed box in designer

Ported

Net volume3.46 ft³ (98 L)
Tuning (Fb)25 Hz
Portslot 2 9/16 × 19 1/16″, 54 1/2″ long
Port velocity at 2,750 W100 ft/s
F3 (−3 dB, no cabin gain)21 Hz
Example box (outside)31 1/2″ × 20 1/2″ × 18 3/8″

The volume and tuning are the recommendation, but the port doesn’t fit this example box. Size the box and port in the designer.

Open ported box in designer
203040506080100150200606672788490HzdB
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Fs25.6 Hz
Qts0.48
Qes0.55
Qms4.03
Vas0.62 ft³
Re (one coil)1.87 Ω
Sd≈ 180.6 in²
Xmax1.18″
EBP47 — suits sealed calc.
Sensitivity, 1 W / 1 m79.3 dB calc.

General

Size18″
Voice coilsdual 2 Ω
RMS power2,750 W

Mounting dimensions

Ø18 7/16″cutout Ø16 11/16″mounting depth 15″magnet Ø9 1/4″
Cutout diameter16 11/16″
Mounting depth15″
Overall diameter18 7/16″
Magnet diameter9 1/4″

The spec sheet's Sd of 254.5 in² is the area of a 18″ circle, not the cone's radiating area — not used.

“≈” 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

Other Sundown Audio 18″ models