Ported box size for 3 12" subs
3 12" subs usually want 5.25–8.25 ft³ net (149–234 L) in a ported box. Your sub’s manual wins: if it gives a volume, build to that.
Example: 6.75 ft³ (191.1 L) net in 3/4" MDF is a box 49 13/16" × 15" × 24" outside (width × height × depth), with a 7" × 13 1/2" slot port 28 13/16" long for 32 Hz. The port takes 1.75 ft³ (49.4 L), already counted in that size.
The 28 13/16" port is longer than the box is deep inside (22 1/2"): fold it into an L along the side or the back.
Example box for 6.75 ft³ (191.1 L) net
Example box for 6.75 ft³ (191.1 L) net| What | Size |
|---|
| Outside (W × H × D) | 49 13/16" × 15" × 24" (1,266 × 381 × 610 mm) |
|---|
| Inside (W × H × D) | 48 5/16" × 13 1/2" × 22 1/2" |
|---|
| Gross volume | 8.5 ft³ (240.6 L) |
|---|
| Slot port | 7" wide × 13 1/2" tall (94.5 sq in) |
|---|
| Port length | 28 13/16" (732 mm) for 32 Hz |
|---|
| Port takes up | 1.75 ft³ (49.4 L) |
|---|
| Net volume | 6.75 ft³ (191.1 L) |
|---|
Cut sheet for the example box (3/4" MDF)
Cut sheet for the example box (3/4" MDF)| Piece | Qty | Size |
|---|
| Front (baffle) | 1 | 49 13/16" × 15" |
|---|
| Back | 1 | 49 13/16" × 15" |
|---|
| Top and bottom | 2 | 49 13/16" × 22 1/2" |
|---|
| Sides | 2 | 13 1/2" × 22 1/2" |
|---|
Same slot port at other tunings
Same slot port at other tunings| Tuning | Slot length |
|---|
| 30 Hz | 33 7/8" (861 mm) |
|---|
| 32 Hz | 28 13/16" (732 mm) |
|---|
| 34 Hz | 24 5/8" (625 mm) |
|---|
| 36 Hz | 21 1/16" (536 mm) |
|---|
Typical net volume for 12" subs
Typical net volume for 12" subs| Subs | Sealed | Ported |
|---|
| 1 | 1–1.6 ft³ | 1.75–2.75 ft³ |
|---|
| 2 | 2–3.2 ft³ | 3.5–5.5 ft³ |
|---|
| 3 | 3–4.8 ft³ | 5.25–8.25 ft³ |
|---|
| 4 | 4–6.4 ft³ | 7–11 ft³ |
|---|
Before you cut
Take off the sub’s own displacement (in its manual, often 0.05 to 0.2 ft³ per sub) and any bracing: the box calculator does that and redoes the width.
Measure the space twice, including the angle of the seat back in a truck cab. A wedge box often fits where a rectangle doesn’t.
Volume ranges are common starting points for car subs, not a standard. The example uses the middle of the range, 3/4" MDF, and for ported boxes a slot port of 14 sq in per ft³ tuned to 32 Hz along the full inside height.
Other box sizes for 12" subs
Frequently asked questions
What size ported box for 3 12" subs?
3 12" subs usually want 5.25–8.25 ft³ net (149–234 L) in a ported box. Your sub’s manual wins: if it gives a volume, build to that.
What are the dimensions of a ported box for 3 12" subs?
Example: 6.75 ft³ (191.1 L) net in 3/4" MDF is a box 49 13/16" × 15" × 24" outside (width × height × depth), with a 7" × 13 1/2" slot port 28 13/16" long for 32 Hz. The port takes 1.75 ft³ (49.4 L), already counted in that size.
What should a ported box for 3 12" subs be tuned to?
Most daily boxes are tuned between 30 and 36 Hz. Lower goes deeper and needs a longer port; higher hits harder up top. Your sub’s manual may suggest a tuning.