DD Audio 9921c D1

21″ subwoofer · dual 1 Ω · 3,200 W RMS

Fs 26.2 HzQts 0.47Vas 5.72 ft³Xmax 1.26″

Recommended box

For a sedan, one sub, 3,200 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 volume3.04 ft³ (86 L)
Qtc0.80
Fc45 Hz
F3 (−3 dB, no cabin gain)42 Hz
Example box (outside)22 7/16″ × 22 7/16″ × 14 3/8″
Open sealed box in designer

Ported

Net volume6.99 ft³ (198 L)
Tuning (Fb)28 Hz
Portslot 5 1/8 × 21 13/16″, 45 11/16″ long
Port velocity at 3,200 W64 ft/s
F3 (−3 dB, no cabin gain)25 Hz
Example box (outside)31 1/2″ × 23 1/4″ × 29 3/16″
Open ported box in designer
203040506080100150200667278849096HzdB
Sealed Ported · SPL in dB at 1 W / 1 m, no cabin gain

Thiele/Small parameters

Fs26.2 Hz
Qts0.47
Qes0.517
Qms5.27
Vas5.72 ft³
Re (one coil)≈ 0.85 Ω
Sd≈ 180.6 in²
Xmax1.26″
EBP51 — sealed or ported calc.
Sensitivity, 1 W / 1 m89.5 dB calc.

General

Size21″
Voice coilsdual 1 Ω
RMS power3,200 W

Mounting dimensions

Ø21 5/16″cutout Ø19 1/4″mounting depth 11 5/16″magnet Ø≈ 12 1/2″
Cutout diameter19 1/4″
Mounting depth11 5/16″
Overall diameter21 5/16″

“≈” 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