Ground Zero GZPW 21SPL (2x1 Ohm)
21″ subwoofer · dual 1 Ω · 7,000 W RMS
Fs 34.5 HzQts 0.55Vas 3.95 ft³
Recommended box
For a sedan, one sub, 7,000 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 volume | 3.57 ft³ (101 L) |
|---|---|
| Qtc | 0.80 |
| Fc | 50 Hz |
| F3 (−3 dB, no cabin gain) | 47 Hz |
| Example box (outside) | 22 13/16″ × 22 13/16″ × 15 15/16″ |
Ported
| Net volume | 6.99 ft³ (198 L) |
|---|---|
| Tuning (Fb) | 32 Hz |
| Port | slot 5 7/8 × 22 3/16″, 39 1/2″ long |
| Port velocity at 7,000 W | 86 ft/s |
| F3 (−3 dB, no cabin gain) | 29 Hz |
| Example box (outside) | 31 1/2″ × 23 5/8″ × 28 5/8″ |
Thiele/Small parameters
| Fs | 34.5 Hz |
|---|---|
| Qts | 0.55 |
| Qes | 0.606 |
| Qms | 6 |
| Vas | 3.95 ft³ |
| Re (one coil) | ≈ 0.85 Ω |
| Sd | ≈ 180.6 in² |
| Xmax | ≈ 0.39″ |
| EBP | 57 — sealed or ported calc. |
| Sensitivity, 1 W / 1 m | 90.8 dB calc. |
General
| Size | 21″ |
|---|---|
| Voice coils | dual 1 Ω |
| RMS power | 7,000 W |
Mounting dimensions
| Cutout diameter | 19 11/16″ |
|---|---|
| Mounting depth | 12 5/8″ |
| Overall diameter | 21 7/16″ |
Only Qts is published — Qms assumed to be 6 and Qes calculated (barely affects box design).
“≈” 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.