Diamond M3121
12″ subwoofer · 4 Ω · 200 W RMS
| Source | web.archive.org · manufacturer data |
|---|---|
| Checked against source | October 2026 |
| Thiele/Small parameters | not in the spec sheet: Re — typical value for the size used |
| Mounting dimensions | 3 of 4 — missing: magnet diameter; the designer will use an estimate |
Recommended box
For a sedan, one sub, 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
smaller, tighter| Bass character (Qtc) | Tight and punchy · 0.80 |
|---|---|
| Fc | 55 Hz |
| F3 (−3 dB, no cabin gain) | 53 Hz |
| Example box (outside) | 14 3/16″ × 14 3/16″ × 16 1/16″ |
Ported
deeper, louder| Tuning (Fb) | 31 Hz |
|---|---|
| Port | slot 1 9/16 × 14 5/16″, 23″ long |
| Port velocity at 200 W | 42 ft/s |
| F3 (−3 dB, no cabin gain) | 33 Hz |
| Example box (outside) | 31 1/2″ × 15 3/4″ × 12 13/16″ |
Deeper: 3.07 ft³ (87 L) tuned to 33 Hz, 31 1/2″ × 15 3/4″ × 15 1/8″ 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 | 200 W |
| Fs | 28 Hz |
| Qts | 0.40 |
| Qes | 0.43 |
| Qms | 6.3 |
| Vas | 3.71 ft³ |
| Re | ≈ 3.4 Ω |
|---|---|
| Sd | 79.1 in² |
| Xmax | 0.31″ |
| Vd | 24.9 in³ calc. |
| Mms | 113 g calc. |
| BL | 12.6 T·m calc. |
| EBP | 65 — sealed or ported calc. |
| Sensitivity, 1 W / 1 m | 89.3 dB calc. |
Mounting dimensions
| Cutout diameter | 11 1/8″ |
|---|---|
| Mounting depth | 5 3/8″ |
| Overall diameter | 12 1/4″ |
“≈” 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 Diamond 12″ models
- Diamond CM312D2 12″ · dual 2 Ω
- Diamond CM312D4 12″ · dual 4 Ω
- Diamond D122 12″ · dual 2 Ω
- Diamond D124 12″ · dual 4 Ω
- Diamond D312D2 12″ · dual 2 Ω
- Diamond D312D4 12″ · dual 4 Ω
- Diamond D612D2 12″ · dual 2 Ω
- Diamond D612D4 12″ · dual 4 Ω
- Diamond D912D2 12″ · dual 2 Ω
- Diamond D912D4 12″ · dual 4 Ω
- Diamond DE122 12″ · dual 2 Ω
- Diamond DE124 12″ · dual 4 Ω
Similar 12″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Gladen RS 12 (SVC 4 ohm) 1.24 ft³ sealed · 2.26 ft³ ported
- Clarion WG3020 1.34 ft³ sealed · 2.40 ft³ ported
- Gladen M 12 (SVC 4 ohm) 1.09 ft³ sealed · 2.26 ft³ ported
- Soundstream EXACT 12 1.09 ft³ sealed · 2.44 ft³ ported
- Gladen Zero 12 Pro (SVC 4 ohm) 0.95 ft³ sealed · 2.33 ft³ ported
- Kenwood KFC-W112S 1.62 ft³ sealed · 1.34 ft³ ported
FAQ
What box does the Diamond M3121 need?
Recommended net volume: 1.27 ft³ sealed, 2.33 ft³ ported tuned to 31 Hz — for one sub in a sedan at 200 W. Fit the box to your space and amp in the free calculator, with plans and a cut sheet.
What are the Diamond M3121 Thiele/Small specs?
Fs 28 Hz, Qts 0.40, Vas 3.71 ft³, Xmax 0.31″, Sd 79.1 in².
What is the Diamond M3121 mounting depth?
Mounting depth is 5 3/8″, cutout diameter 11 1/8″. The inside depth of the box must exceed the mounting depth by at least 1″.
How much power does the Diamond M3121 handle and how do I wire it?
RMS power rating: 200 W. Wiring for several subs and amp power — in the wiring calculator.