Ported box size for 3 15" subs
3 15" subs usually want 8.25–13.5 ft³ net (234–382 L) in a ported box. Your sub’s manual wins: if it gives a volume, build to that.
Example: 10.88 ft³ (307.9 L) net in 3/4" MDF is a box 54 1/2" × 18" × 28" outside (width × height × depth), with a 9 1/4" × 16 1/2" slot port 26 11/16" long for 32 Hz. The port takes 2.54 ft³ (71.9 L), already counted in that size.
The 26 11/16" port is longer than the box is deep inside (26 1/2"): fold it into an L along the side or the back.
Example box for 10.88 ft³ (307.9 L) net
Example box for 10.88 ft³ (307.9 L) net| What | Size |
|---|
| Outside (W × H × D) | 54 1/2" × 18" × 28" (1,385 × 457 × 711 mm) |
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| Inside (W × H × D) | 53" × 16 1/2" × 26 1/2" |
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| Gross volume | 13.41 ft³ (379.9 L) |
|---|
| Slot port | 9 1/4" wide × 16 1/2" tall (152.3 sq in) |
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| Port length | 26 11/16" (677 mm) for 32 Hz |
|---|
| Port takes up | 2.54 ft³ (71.9 L) |
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| Net volume | 10.88 ft³ (307.9 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 | 54 1/2" × 18" |
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| Back | 1 | 54 1/2" × 18" |
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| Top and bottom | 2 | 54 1/2" × 26 1/2" |
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| Sides | 2 | 16 1/2" × 26 1/2" |
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Same slot port at other tunings
Same slot port at other tunings| Tuning | Slot length |
|---|
| 30 Hz | 31 3/4" (806 mm) |
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| 32 Hz | 26 11/16" (677 mm) |
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| 34 Hz | 22 7/16" (570 mm) |
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| 36 Hz | 18 15/16" (481 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 3 15" subs?
3 15" subs usually want 8.25–13.5 ft³ net (234–382 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 15" subs?
Example: 10.88 ft³ (307.9 L) net in 3/4" MDF is a box 54 1/2" × 18" × 28" outside (width × height × depth), with a 9 1/4" × 16 1/2" slot port 26 11/16" long for 32 Hz. The port takes 2.54 ft³ (71.9 L), already counted in that size.
What should a ported box for 3 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.