Ported box size for 2 15" subs
2 15" subs usually want 5.5–9 ft³ net (156–255 L) in a ported box. Your sub’s manual wins: if it gives a volume, build to that.
Example: 7.25 ft³ (205.3 L) net in 3/4" MDF is a box 44" × 18" × 24" outside (width × height × depth), with a 6 1/8" × 16 1/2" slot port 28 1/2" long for 32 Hz. The port takes 1.88 ft³ (53.2 L), already counted in that size.
The 28 1/2" 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 7.25 ft³ (205.3 L) net
Example box for 7.25 ft³ (205.3 L) net| What | Size |
|---|
| Outside (W × H × D) | 44" × 18" × 24" (1,118 × 457 × 610 mm) |
|---|
| Inside (W × H × D) | 42 1/2" × 16 1/2" × 22 1/2" |
|---|
| Gross volume | 9.13 ft³ (258.5 L) |
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| Slot port | 6 1/8" wide × 16 1/2" tall (101.5 sq in) |
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| Port length | 28 1/2" (725 mm) for 32 Hz |
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| Port takes up | 1.88 ft³ (53.2 L) |
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| Net volume | 7.25 ft³ (205.3 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 |
|---|
| Front (baffle) | 1 | 44" × 18" |
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| Back | 1 | 44" × 18" |
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| Top and bottom | 2 | 44" × 22 1/2" |
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| Sides | 2 | 16 1/2" × 22 1/2" |
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Same slot port at other tunings
Same slot port at other tunings| Tuning | Slot length |
|---|
| 30 Hz | 33 5/8" (854 mm) |
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| 32 Hz | 28 1/2" (725 mm) |
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| 34 Hz | 24 5/16" (618 mm) |
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| 36 Hz | 20 13/16" (528 mm) |
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Typical net volume for 15" subs
Typical net volume for 15" subs| Subs | Sealed | Ported |
|---|
| 1 | 1.75–2.75 ft³ | 2.75–4.5 ft³ |
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| 2 | 3.5–5.5 ft³ | 5.5–9 ft³ |
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| 3 | 5.25–8.25 ft³ | 8.25–13.5 ft³ |
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| 4 | 7–11 ft³ | 11–18 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 15" subs
Frequently asked questions
What size ported box for 2 15" subs?
2 15" subs usually want 5.5–9 ft³ net (156–255 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 15" subs?
Example: 7.25 ft³ (205.3 L) net in 3/4" MDF is a box 44" × 18" × 24" outside (width × height × depth), with a 6 1/8" × 16 1/2" slot port 28 1/2" long for 32 Hz. The port takes 1.88 ft³ (53.2 L), already counted in that size.
What should a ported box for 2 15" 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.