Sealed box size for 3 8" subs
3 8" subs usually want 1.05–1.8 ft³ net (30–51 L) in a sealed box. Your sub’s manual wins: if it gives a volume, build to that.
Example: 1.42 ft³ (40.4 L) net in 3/4" MDF is a box 24 1/16" × 11" × 13" outside (width × height × depth).
Example box for 1.42 ft³ (40.4 L) net
Example box for 1.42 ft³ (40.4 L) net| What | Size |
|---|
| Outside (W × H × D) | 24 1/16" × 11" × 13" (611 × 279 × 330 mm) |
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| Inside (W × H × D) | 22 9/16" × 9 1/2" × 11 1/2" |
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| Gross volume | 1.42 ft³ (40.4 L) |
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| Net volume | 1.42 ft³ (40.4 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 | 24 1/16" × 11" |
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| Back | 1 | 24 1/16" × 11" |
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| Top and bottom | 2 | 24 1/16" × 11 1/2" |
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| Sides | 2 | 9 1/2" × 11 1/2" |
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Typical net volume for 8" subs
Typical net volume for 8" subs| Subs | Sealed | Ported |
|---|
| 1 | 0.35–0.6 ft³ | 0.6–1 ft³ |
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| 2 | 0.7–1.2 ft³ | 1.2–2 ft³ |
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| 3 | 1.05–1.8 ft³ | 1.8–3 ft³ |
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| 4 | 1.4–2.4 ft³ | 2.4–4 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 8" subs
Frequently asked questions
What size sealed box for 3 8" subs?
3 8" subs usually want 1.05–1.8 ft³ net (30–51 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 8" subs?
Example: 1.42 ft³ (40.4 L) net in 3/4" MDF is a box 24 1/16" × 11" × 13" outside (width × height × depth).
Should a 8" 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.