Polk Audio db1240
12″ subwoofer · 4 Ω · 360 W RMS
The Polk Audio db1240 is a 12″ subwoofer. With Qts 0.44 and EBP 65 it works both sealed and ported: sealed is tighter and smaller, ported is deeper and louder. Modest excursion (Xmax 0.30″) — for clean sound at moderate levels, not for SPL competitions.
| Source | web.archive.org · manufacturer data |
|---|---|
| Checked against source | October 2026 |
| Thiele/Small parameters | complete |
| Mounting dimensions | 2 of 4 — missing: frame outer diameter, magnet diameter; the designer will use an estimate |
Recommended box
For a sedan, one sub, 360 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) | Tight and punchy · 0.80 |
|---|---|
| Fc | 55 Hz |
| F3 (−3 dB, no cabin gain) | 52 Hz |
| Example box (outside) | 14 3/16″ × 14 3/16″ × 14 3/16″ |
Ported
deeper, louder| Tuning (Fb) | 33 Hz |
|---|---|
| Port | slot 1 9/16 × 14 5/16″, 23 5/8″ long |
| Port velocity at 360 W | 58 ft/s |
| F3 (−3 dB, no cabin gain) | 33 Hz |
| Example box (outside) | 31 1/2″ × 15 3/4″ × 11 5/8″ |
Deeper: 3.11 ft³ (88 L) tuned to 31 Hz, 31 1/2″ × 15 3/4″ × 16″ 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 | 12″ |
|---|---|
| Voice coils | 4 Ω |
| RMS power | 360 W |
| Fs | 30 Hz |
| Qts | 0.44 |
| Qes | 0.46 |
| Qms | 10.4 |
| Vas | 2.54 ft³ |
| Re | 3.5 Ω |
|---|---|
| Sd | 80.6 in² |
| Xmax | 0.30″ |
| Vd | 23.8 in³ calc. |
| Mms | 150 g calc. |
| BL | 14.7 T·m calc. |
| EBP | 65 — sealed or ported calc. |
| Sensitivity, 1 W / 1 m | 88.3 dB calc. |
Mounting dimensions
| Cutout diameter | 11″ |
|---|---|
| Mounting depth | 6″ |
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.
- 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
- FJ Cruiser — behind the rear seat sealed and ported box
- El Camino 1978–87 — 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
- Club Car Precedent — under the rear seat sealed 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 Polk Audio 12″ models
- Polk Audio db124 12″ · 4 Ω
- Polk Audio db124DVC 12″ · dual 4 Ω
- Polk Audio db1240DVC 12″ · dual 4 Ω
- Polk Audio dX12-4 12″ · 4 Ω
- Polk Audio dX12-8 12″ · 8 Ω
- Polk Audio DXi124 DVC 12″ · dual 4 Ω
- Polk Audio DXi124 SVC 12″ · 4 Ω
- Polk Audio DXi1240DVC 12″ · dual 4 Ω
- Polk Audio EX12 (EX Series II) 12″ · 4 Ω
- Polk Audio GXR124 12″ · 4 Ω
- Polk Audio MM120-4 12″ · 4 Ω
- Polk Audio MM124 (Polk/MOMO) 12″ · 4 Ω
Similar 12″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- SPL Dynamics V-300S4 1.31 ft³ sealed · 2.01 ft³ ported
- Sundown Audio Ev2-12 D4 1.02 ft³ sealed · 2.08 ft³ ported
- American Bass TM-1244 1.02 ft³ sealed · 1.91 ft³ ported
- Audioque SDC2.012 D4 1.09 ft³ sealed · 1.91 ft³ ported
- American Bass TM-1222 0.95 ft³ sealed · 1.84 ft³ ported
- Black Hydra Gamma-12 1.31 ft³ sealed · 1.87 ft³ ported
FAQ
What box does the Polk Audio db1240 need?
Recommended net volume: 1.09 ft³ sealed, 2.01 ft³ ported tuned to 33 Hz — for one sub in a sedan at 360 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.
What are the Polk Audio db1240 Thiele/Small specs?
Fs 30 Hz, Qts 0.44, Vas 2.54 ft³, Xmax 0.30″, Sd 80.6 in².
What is the Polk Audio db1240 mounting depth?
Mounting depth is 6″, cutout diameter 11″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Polk Audio db1240 handle and how do I wire it?
RMS power rating: 360 W. Wiring for several subs and amp power — in the wiring calculator.
Is the Polk Audio db1240 better sealed or ported?
EBP 65: both work — sealed 1.09 ft³ is tighter and smaller, ported 2.01 ft³ tuned to 33 Hz is deeper and louder.
What port does the Polk Audio db1240 need?
For the 2.01 ft³ ported box tuned to 33 Hz: slot 1 9/16 × 14 5/16″, 23 5/8″ long, area 22.6 in²; or a round port Ø5 3/8″, ≈ 23 5/8″ long. Port air speed at 360 W: 58 ft/s.
What box do two Polk Audio db1240 subs need?
Two subs need twice the volume: 2.19 ft³ sealed, or 4.03 ft³ ported at the same 33 Hz tuning with twice the port area. One shared chamber or one per sub — whatever fits your vehicle.