Enter Speaker Box Details
Example Data Table
| Box style | Outside size | Material | Displacement | Expected use |
|---|---|---|---|---|
| Sealed rectangular | 24 in × 14 in × 14 in | 0.75 in | 0.12 cu ft | Compact subwoofer cabinet |
| Ported rectangular | 30 in × 16 in × 18 in | 0.75 in | 0.20 cu ft plus port | Higher bass output |
| Wedge sealed | 28 in × 15 in × 10/16 in | 0.75 in | 0.10 cu ft | Vehicle trunk build |
Formula Used
Rectangular gross volume: internal width × internal height × internal depth.
Wedge gross volume: internal width × internal height × average internal depth.
Average internal depth: (internal front depth + internal back depth) ÷ 2.
Net volume: gross volume − driver displacement − brace displacement − terminal displacement − port displacement.
Round port displacement: π × radius² × port length × number of ports.
Slot port displacement: slot width × slot height × port length × number of ports.
Port tuning estimate: speed of sound ÷ 2π × square root of port area ÷ box volume and effective length.
How to Use This Calculator
- Select sealed or ported box type.
- Choose rectangular or wedge shape.
- Enter outside dimensions and material thickness.
- Add driver, brace, terminal, and port displacement values.
- Enter a target net volume from the driver manual.
- Press Calculate Volume to review the result.
- Use CSV or PDF buttons to save the result.
Speaker Box Volume Planning Guide
Why Speaker Box Volume Matters
A speaker box is more than a wooden case. It controls the air spring behind the driver. That air spring changes bass output, cone control, and efficiency. A small sealed box gives tight response. It can also reduce deep bass. A large box may play lower. It can also sound loose when the driver is not suited.
Gross, Net, and Displacement
Builders often confuse gross volume with net volume. Gross volume is the internal space before parts are removed. Net volume is the usable air volume after removing driver, port, brace, and terminal cup displacement. Most driver manuals list a recommended net volume. That value should be compared with the calculator result, not the raw cabinet size.
Sealed and Ported Planning
A sealed enclosure is simpler. You mainly match the recommended net volume. Then you add displacement allowances. A ported enclosure needs extra care. The port tube or slot occupies space. Its air path also sets tuning frequency. Longer ports usually tune lower. Larger ports reduce noise, but they take more room.
Wedge and Vehicle Boxes
Many car audio boxes use a wedge shape. The average depth method gives a practical volume estimate. Measure the front depth and back depth. The calculator averages them after material thickness is removed. This works well for straight sloped panels. Complex curves need separate section estimates.
Material Thickness
Material thickness must be subtracted from outside dimensions. A box built from thick panels may lose a surprising amount of air space. This is why outside measurements alone can mislead. Enter the actual board thickness. Use the same unit as the cabinet dimensions.
Cutting and Checking
Always test your numbers before cutting panels. Compare the net volume with the driver target. Check port displacement. Review brace allowance. Leave space for the magnet, wiring, and damping material. A careful plan prevents wasted wood and weak bass. It also makes the finished enclosure easier to build and tune.
Practical Accuracy Tips
Use water resistant glue and square joints. Small leaks change performance. Round port edges when possible. Keep braces strong, but include their volume. Recheck every length after saw setup. Small dimension errors become larger volume errors. Record final values for future repairs.
FAQs
What is speaker box net volume?
Net volume is the usable air space inside the enclosure. It remains after subtracting the driver, bracing, terminal cup, and port volume from the gross internal volume.
Why does material thickness matter?
Material thickness reduces the inside dimensions. Even a small thickness change can create a large volume difference, especially in compact subwoofer boxes.
Should I use outside or inside dimensions?
Enter outside dimensions when using this calculator. It subtracts material thickness to estimate internal dimensions and usable air space.
What is driver displacement?
Driver displacement is the volume taken by the speaker basket and magnet inside the cabinet. Many speaker manuals list this value.
Does a port reduce box volume?
Yes. A port occupies physical space inside the cabinet. The calculator subtracts round or slot port displacement when ported mode is selected.
Can I calculate a wedge box?
Yes. Select wedge shape and enter front and back depths. The calculator uses average internal depth for a practical slanted box estimate.
What is fill allowance?
Fill allowance estimates the apparent volume gain from damping material. It is mainly useful for sealed enclosures, not as a fix for poor sizing.
Is the tuning frequency exact?
No. It is an estimate based on port area, length, and net volume. Real tuning can change with flares, bends, leakage, and wall effects.