Box for two 12 inch subwoofers
Two 12 inch subwoofers usually need 1.5–3 ft³ (42–85 L) in a sealed box or 3–5 ft³ (85–142 L) in a ported box tuned to about 30–35 Hz, in total. That is simply double the volume of one 12″ sub; the box also has to be wide enough to put both subs side by side.
Dual 12 inch sub box size chart
| Sealed | Ported | |
|---|---|---|
| Net volume, both subs | 1.5–3 ft³ (42–85 L) | 3–5 ft³ (85–142 L) |
| Per sub | 0.75–1.5 ft³ (21–42 L) | 1.5–2.5 ft³ (42–71 L) |
| Port tuning | — | 30–35 Hz |
| Port area, both subs | — | 36–80 in² (230–520 cm²) |
| Amplifier power | about 1400 W RMS (2 × 700 W, a typical 12″ sub in our database) | |
As with one sub, these are the ranges most manufacturers print, not an answer for your exact model. If the manual of your sub gives a recommended box, take that volume and double it. The size of a box for a single 12 is on the 12 inch subwoofer box page.
12 inch dual sub box dimensions: ready-made plans
Two ready-made boxes for a pair of typical 12″ subs: 11 1/8″ cutout, 6 1/2″ mounting depth (the middle of the models in our database), subs side by side in one shared chamber. Volumes come from the chart above, 3/4″ sheet, all dimensions are outside. Before you cut, check the cutout and depth against your subs, or open the plan in the calculator and pick your model: the dimensions update.
Two 12″ sealed box
27 1/2″ × 15″ × 13 3/8″
Outside: width × height × depth
| Net volume | 2.20 ft³ |
|---|---|
| Inside depth | 11 7/8″ |
| Sheet | 3/4″ |
Cut list
| Panel | Qty | Size |
|---|---|---|
| Top / bottom | 2 | 27 1/2″ × 13 3/8″ |
| Baffle | 1 | 27 1/2″ × 13 1/2″ |
| Back panel | 1 | 27 1/2″ × 13 1/2″ |
| Side panels | 2 | 11 7/8″ × 13 1/2″ |
Two 12″ ported box
31 1/2″ × 19″ × 19 11/16″
Outside: width × height × depth
| Net volume | 4.00 ft³ |
|---|---|
| Tuning (Fb) | 33 Hz |
| Port | slot 3 9/16 × 17 1/2″, 31 9/16″ long |
| Inside depth | 18 3/16″ |
| Sheet | 3/4″ |
Cut list
| Panel | Qty | Size |
|---|---|---|
| Top / bottom | 2 | 31 1/2″ × 19 11/16″ |
| Baffle | 1 | 27 3/16″ × 17 1/2″ |
| Back panel | 1 | 31 1/2″ × 17 1/2″ |
| Left side panel (port side) | 1 | 18 15/16″ × 17 1/2″ |
| Right side panel | 1 | 18 3/16″ × 17 1/2″ |
| Port wall (along side) | 1 | 13 7/8″ × 17 1/2″ |
| Port wall (along back) | 1 | 12 5/8″ × 17 1/2″ |
One shared chamber or two separate chambers?
- Shared chamber. Two identical subs in one box of double volume behave exactly like each sub in its own box of half that volume. It is the simplest build and the most common one: one box, one port, no divider.
- Separate chambers. A divider panel gives each sub its own volume. Use it when the subs are not identical (different models or different Fs, Qts, Vas), when each sub has its own amp channel with different settings, or so that a blown sub does not change how the other one loads. Each chamber gets half the volume and, in a ported box, its own port of half the area tuned to the same frequency.
- One port or two? In a shared ported box one large port is easier to build and has less turbulence than two small ones with the same total area. Two ports are fine too, as long as the total area and the tuning stay the same.
How to wire two 12 inch subs
| Two subs | Final load you can get | Usual choice |
|---|---|---|
| Single 4 Ω voice coil (SVC 4) | 2 Ω (parallel), 8 Ω (series) | 2 Ω |
| Single 2 Ω voice coil (SVC 2) | 1 Ω (parallel), 4 Ω (series) | 1 Ω on a 1 Ω stable amp, otherwise 4 Ω |
| Dual 4 Ω voice coils (DVC 4) | 1 Ω, 4 Ω, 16 Ω | 1 Ω or 4 Ω |
| Dual 2 Ω voice coils (DVC 2) | 0.5 Ω, 2 Ω, 8 Ω | 2 Ω |
A mono amp makes the most power at the lowest load it is rated for, so pick the wiring that lands on that load or the next one up, never below it. Both subs must be wired the same way and in phase (+ to + on both), otherwise they cancel each other. The calculator shows every wiring option for the subs you pick and the load your amp sees.
Box width for two 12″ subs
Two 12″ subs side by side need a baffle at least about 28.75″ (730 mm) wide outside: two typical frames, a little space between and around them, and the side walls. A slot port along the side adds its own width. If the trunk is not that wide, stand the subs one above the other in a taller box, or fire them up or back.
Depth is the same as for one sub: the typical 12″ sub in our database needs 6.5″ (165 mm) of mounting depth, and 1 in 10 need 9.5″ (244 mm) or more, plus about an inch behind the magnet.
Get the exact box for your two subs
Pick your 12 inch model in the calculator, set the number of subs to 2, and it gives the volume, port, wiring options, the response in your car, and the plans and cut sheet for the whole box. It is free and works in inches or millimeters.
Model it for your own subResponse in your car, cone excursion and port air speed — free, no signup.Open the calculator →FAQ
What are the dimensions of a dual 12 inch sub box?
For two typical 12″ subs, a 4.00 ft³ ported box tuned to 33 Hz comes out at about 31 1/2″ × 19″ × 19 11/16″ outside, and a 2.20 ft³ sealed box at about 27 1/2″ × 15″ × 13 3/8″ (3/4″ sheet, subs side by side). The exact size depends on your subs’ cutout, depth and parameters.
What size box do I need for two 12 inch subs?
Double the volume of one sub: most pairs of 12 inch car subwoofers want about 1.5–3 ft³ (42–85 L) sealed or 3–5 ft³ (85–142 L) ported in total, tuned around 30–35 Hz. That is net volume, after both drivers, the port and bracing are taken out.
Should two 12s share one chamber or have separate chambers?
With two identical subs on one amp, one shared chamber works the same as two chambers of half the volume each, and it is simpler to build. Separate chambers make sense when the subs are different, when you want to run them on different amps, or so that one blown sub cannot drag the other one with it.
How do I wire two dual 4 ohm 12 inch subs?
Two dual 4 Ω subs can be wired to 1 Ω (all four coils in parallel), 4 Ω (each sub’s coils in series to 8 Ω, then the two subs in parallel) or 16 Ω. Most mono amps are rated at 1 Ω or 2 Ω, so 1 Ω gives the most power if your amp is 1 Ω stable, and 4 Ω is the safe choice for anything else.