Ported box size for 2 12" subs
2 12" subs usually want 3.5–5.5 ft³ net (99–156 L) in a ported box. Your sub’s manual wins: if it gives a volume, build to that.
Example: 4.5 ft³ (127.4 L) net in 3/4" MDF is a box 41 1/2" × 15" × 20" outside (width × height × depth), with a 4 11/16" × 13 1/2" slot port 30 5/16" long for 32 Hz. The port takes 1.28 ft³ (36.3 L), already counted in that size.
The 30 5/16" port is longer than the box is deep inside (18 1/2"): fold it into an L along the side or the back.
Example box for 4.5 ft³ (127.4 L) net
Example box for 4.5 ft³ (127.4 L) net| What | Size |
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| Outside (W × H × D) | 41 1/2" × 15" × 20" (1,054 × 381 × 508 mm) |
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| Inside (W × H × D) | 40" × 13 1/2" × 18 1/2" |
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| Gross volume | 5.78 ft³ (163.7 L) |
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| Slot port | 4 11/16" wide × 13 1/2" tall (63 sq in) |
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| Port length | 30 5/16" (769 mm) for 32 Hz |
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| Port takes up | 1.28 ft³ (36.3 L) |
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| Net volume | 4.5 ft³ (127.4 L) |
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Cut sheet for the example box (3/4" MDF)
Cut sheet for the example box (3/4" MDF)| Piece | Qty | Size |
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| Front (baffle) | 1 | 41 1/2" × 15" |
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| Back | 1 | 41 1/2" × 15" |
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| Top and bottom | 2 | 41 1/2" × 18 1/2" |
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| Sides | 2 | 13 1/2" × 18 1/2" |
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Same slot port at other tunings
Same slot port at other tunings| Tuning | Slot length |
|---|
| 30 Hz | 35 3/8" (898 mm) |
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| 32 Hz | 30 5/16" (769 mm) |
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| 34 Hz | 26 1/16" (663 mm) |
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| 36 Hz | 22 9/16" (573 mm) |
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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 |
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| 2 | 2–3.2 ft³ | 3.5–5.5 ft³ |
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| 3 | 3–4.8 ft³ | 5.25–8.25 ft³ |
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| 4 | 4–6.4 ft³ | 7–11 ft³ |
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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 2 12" subs?
2 12" subs usually want 3.5–5.5 ft³ net (99–156 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 2 12" subs?
Example: 4.5 ft³ (127.4 L) net in 3/4" MDF is a box 41 1/2" × 15" × 20" outside (width × height × depth), with a 4 11/16" × 13 1/2" slot port 30 5/16" long for 32 Hz. The port takes 1.28 ft³ (36.3 L), already counted in that size.
What should a ported box for 2 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.