Sealed box size for 3 15" subs
3 15" subs usually want 5.25–8.25 ft³ net (149–234 L) in a sealed 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 44 5/16" × 18" × 18" outside (width × height × depth).
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) | 44 5/16" × 18" × 18" (1,126 × 457 × 457 mm) |
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| Inside (W × H × D) | 42 13/16" × 16 1/2" × 16 1/2" |
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| Gross volume | 6.75 ft³ (191.1 L) |
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| Net volume | 6.75 ft³ (191.1 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 5/16" × 18" |
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| Back | 1 | 44 5/16" × 18" |
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| Top and bottom | 2 | 44 5/16" × 16 1/2" |
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| Sides | 2 | 16 1/2" × 16 1/2" |
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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 sealed box for 3 15" subs?
3 15" subs usually want 5.25–8.25 ft³ net (149–234 L) in a sealed box. Your sub’s manual wins: if it gives a volume, build to that.
What are the dimensions of a sealed box for 3 15" subs?
Example: 6.75 ft³ (191.1 L) net in 3/4" MDF is a box 44 5/16" × 18" × 18" outside (width × height × depth).
Should a 15" sub go sealed or ported?
Sealed is smaller and tighter. Ported is louder for the same power and goes deeper, but the box is bigger and needs a port.