Quantum Audio QWX4000/8D4
8″ subwoofer · dual 4 Ω
The Quantum Audio QWX4000/8D4 is a 8″ subwoofer. With Qts 0.41 and EBP 107 it suits a ported box: deeper and louder; sealed, the bass sounds a bit dry.
| Source | web.archive.org · manufacturer data |
|---|---|
| Checked against source | October 2026 |
| Thiele/Small parameters | complete |
| Mounting dimensions | 0 of 4 — missing: cutout, mounting depth, frame outer diameter, magnet diameter; the designer will use an estimate |
Recommended box
For a sedan, one sub, 300 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| Bass character (Qtc) | Dry and tight · 0.54 |
|---|---|
| Fc | 66 Hz |
| F3 (−3 dB, no cabin gain) | 96 Hz |
| Example box (outside) | 10 5/8″ × 10 5/8″ × 7 7/8″ |
Ported
deeper, louder| Tuning (Fb) | 49 Hz |
|---|---|
| Port | round port Ø2 1/2″, 10 1/4″ long |
| Port velocity at 300 W | 163 ft/s |
| F3 (−3 dB, no cabin gain) | 43 Hz |
| Example box (outside) | 13 15/16″ × 15 3/4″ × 6 1/2″ |
At 300 W this example’s port will be noisy: air speed 163 ft/s, while the limit is 82 ft/s. It stays quiet up to about 75 W. Full power needs a port of at least 9.9 in², which means a bigger box than this example — size it in the designer.
Open ported box in designerDeeper: 0.57 ft³ (16 L) tuned to 41 Hz, 16 5/8″ × 15 3/4″ × 6 1/2″ outside — a bigger box with flatter deep bass. Open in the calculator
Projects with this subwoofer
Boxes that users designed and published: plans, cut sheet and response graph.
Thiele/Small parameters
| Size | 8″ |
|---|---|
| Voice coils | dual 4 Ω |
| RMS power | — |
| Fs | 51.3 Hz |
| Qts | 0.41 |
| Qes | 0.478 |
| Qms | 3.12 |
| Vas | 0.19 ft³ |
| Re (one coil) | 3.4 Ω |
|---|---|
| Sd | 29.2 in² |
| Xmax | 0.41″ |
| Vd | 12.1 in³ calc. |
| Mms | 90 g calc. |
| BL | 14.4 T·m calc. |
| EBP | 107 — suits ported calc. |
| Sensitivity, 1 W / 1 m | 83.8 dB calc. |
Mounting dimensions
| Cutout diameter | ≈ 7 5/16″ |
|---|---|
| Mounting depth | ≈ 3 15/16″ |
Where it fits in a vehicle
Spots from our vehicle guides where the cutout, mounting depth and recommended box fit. The spot sizes are approximate — measure your own vehicle.
- F-150 SuperCrew — under the rear seat sealed and ported box
- F-150 regular cab — behind the seat sealed and ported box
- Ram Crew Cab — under the rear seat sealed and ported box
- Ram regular cab — behind the seat sealed and ported box
- Tacoma Double Cab — under the rear seat sealed and ported box
- Tacoma Access Cab — behind the front seats sealed and ported box
- Bronco 4-door — behind the rear seat sealed and ported box
- Wrangler 4-door, hard top — behind the rear seat sealed and ported box
- Wrangler 4-door, soft top — behind the rear seat sealed and ported box
- Silverado / Sierra Crew Cab — under the rear seat sealed and ported box
- Silverado / Sierra regular cab — behind the seat sealed and ported box
- Spare tire well sealed and ported box
- Polaris RZR / Ranger — under the seat sealed and ported box
- Can-Am — under the seat sealed and ported box
- Avalanche — under the rear seat sealed and ported box
- FJ Cruiser — behind the rear seat sealed and ported box
- El Camino 1978–87 — behind the seat sealed and ported box
- C10 1973–87 regular cab — behind the seat sealed and ported box
- Cherokee XJ — cargo area, spare moved out sealed and ported box
- Excursion — behind the third row sealed and ported box
- Mustang 2015–2023 coupe — trunk sealed and ported box
- Challenger / Charger — trunk sealed and ported box
- Tesla Model 3 — well under the trunk floor sealed and ported box
- Club Car Precedent — under the rear seat sealed and ported box
“≈” 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 Quantum Audio 8″ models
- Quantum Audio QPW3000/8D4 8″ · dual 4 Ω
- Quantum Audio QW3000/8D4 8″ · dual 4 Ω
Similar 8″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Audioque SDC2.08 D4 0.32 ft³ sealed · 0.53 ft³ ported
- Rockville W8K6D2 V2 0.28 ft³ sealed · 0.67 ft³ ported
- Rockville W8K6D4 V2 0.28 ft³ sealed · 0.67 ft³ ported
- URAL Patriot 8 (2+2) 0.28 ft³ sealed · 0.46 ft³ ported
- Audiopipe TXX-BD3-8 0.28 ft³ sealed · 0.95 ft³ ported
- Machete MF-08S D2 0.32 ft³ sealed · 0.53 ft³ ported
All 8″ subwoofers in our database →
FAQ
What box does the Quantum Audio QWX4000/8D4 need?
Recommended net volume: 0.28 ft³ sealed, 0.46 ft³ ported tuned to 49 Hz — for one sub in a sedan at 300 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.
What are the Quantum Audio QWX4000/8D4 Thiele/Small specs?
Fs 51.3 Hz, Qts 0.41, Vas 0.19 ft³, Xmax 0.41″, Sd 29.2 in².
Is the Quantum Audio QWX4000/8D4 better sealed or ported?
EBP 107: a ported box (0.46 ft³, tuned to 49 Hz) suits it best — deeper and louder. Sealed (0.28 ft³) the bass is drier.
What port does the Quantum Audio QWX4000/8D4 need?
For the 0.46 ft³ ported box tuned to 49 Hz: round port Ø2 1/2″, 10 1/4″ long, area 5 in². Port air speed at 300 W: 163 ft/s.
What box do two Quantum Audio QWX4000/8D4 subs need?
Two subs need twice the volume: 0.57 ft³ sealed, or 0.92 ft³ ported at the same 49 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.