Diamond CM308D4
8″ subwoofer · dual 4 Ω
| Source | web.archive.org · manufacturer data |
|---|---|
| Checked against source | October 2026 |
| Thiele/Small parameters | complete |
| Mounting dimensions | 3 of 4 — missing: 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) | Tight and punchy · 0.79 |
|---|---|
| Fc | 68 Hz |
| F3 (−3 dB, no cabin gain) | 64 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″, 9 3/8″ long |
| Port velocity at 300 W | 159 ft/s |
| F3 (−3 dB, no cabin gain) | 42 Hz |
| Example box (outside) | 14 3/16″ × 15 3/4″ × 6 11/16″ |
At 300 W this example’s port will be noisy: air speed 159 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 9.7 in², which means a bigger box than this example — size it in the designer.
Open ported box in designerDeeper: 0.78 ft³ (22 L) tuned to 37 Hz, 16 5/16″ × 15 3/4″ × 11 7/16″ 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 | 8″ |
|---|---|
| Voice coils | dual 4 Ω |
| RMS power | — |
| Fs | 49 Hz |
| Qts | 0.57 |
| Qes | 0.63 |
| Qms | 6 |
| Vas | 0.26 ft³ |
| Re (one coil) | 3.5 Ω |
|---|---|
| Sd | 31 in² |
| Xmax | 0.32″ |
| Vd | 10 in³ calc. |
| Mms | 81 g calc. |
| BL | 11.8 T·m calc. |
| EBP | 78 — sealed or ported calc. |
| Sensitivity, 1 W / 1 m | 83.4 dB calc. |
Mounting dimensions
| Cutout diameter | 7 3/8″ |
|---|---|
| Mounting depth | 4 1/8″ |
| Overall diameter | 8 1/2″ |
“≈” 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
- web.archive.org/web/20070830083842/http://www.diamondaudio.com/PDF/archive/CM3/C
- web.archive.org/web/20050405075111/http://www.diamondaudio.com:80/products/pdfs/
Other Diamond 8″ models
- Diamond CM308D2 8″ · dual 2 Ω
- Diamond M3080 8″ · 4 Ω
Similar 8″ subwoofers from other brands
Close in Fs, Qts and Vas — a box of similar volume will suit them.
- Alpine S2-W8D2 0.28 ft³ sealed · 0.60 ft³ ported
- Sundown Audio SDv3-8 D2 0.25 ft³ sealed · 0.46 ft³ ported
- CT Sounds BIO-8 D2 0.32 ft³ sealed · 0.49 ft³ ported
- Sundown Audio SML-8 D4 0.32 ft³ sealed · 0.53 ft³ ported
- Phoenix Gold ZXT8D2 (slim, DVC 2 ohm) 0.35 ft³ sealed · 0.53 ft³ ported
- American Bass XD-844 0.32 ft³ sealed · 0.49 ft³ ported
FAQ
What box does the Diamond CM308D4 need?
Recommended net volume: 0.28 ft³ sealed, 0.49 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 Diamond CM308D4 Thiele/Small specs?
Fs 49 Hz, Qts 0.57, Vas 0.26 ft³, Xmax 0.32″, Sd 31 in².
What is the Diamond CM308D4 mounting depth?
Mounting depth is 4 1/8″, cutout diameter 7 3/8″. The inside depth of the box must exceed the mounting depth by at least 1″.