Subwoofer tools.
ENCLOSURES & PORTS / THE TOOLKIT

Enclosure volume.

An enclosure is described by its net acoustic volume, not its outside dimensions. Find the internal volume and see every deduction before you build.

01 / THE INPUTS
Cabinet dimensions
Individual panel overrides

Blank uses the default thickness.

Blank uses the default thickness.

Blank uses the default thickness.

Blank uses the default thickness.

Blank uses the default thickness.

Blank uses the default thickness.

Internal deductions

Include the duct air and material inside the cabinet. Do not count a shared cabinet wall twice.

02 / THE RESULTS
Net enclosure volume
44.88L
Gross internal volume
53.03L
Total deductions
8.15L
Net volume in cubic feet
1.585ft3

Every subtraction, accounted for

ComponentVolume (L)
Gross internal volume53.033
Driver- 3.000
Braces- 1.500
Electronics & hardware- 0.800
Internal port- 2.850
Net acoustic volume44.883

Read this result with its assumptions.

Inside dimensions: 464.0 x 364.0 x 314.0 mm.

Use the net volume in your enclosure model. Include internal duct air and material in port displacement, without subtracting a shared wall twice.

Units & assumptions

Your calculations run in this browser. No account needed.

03 / UNDER THE HOOD

The math, in plain sight.

Count the space the air actually has.

The space the air actually has

Net acoustic volume is the air available after subtracting drivers, internal ducts, braces, and equipment. It is not the external volume or the unoccupied internal volume. For rectangular cabinets with unequal opposing panels:

Li=Lo−tL,1−tL,2,Wi=Wo−tW,1−tW,2,Hi=Ho−tH,1−tH,2L_i=L_o-t_{L,1}-t_{L,2},\quad W_i=W_o-t_{W,1}-t_{W,2},\quad H_i=H_o-t_{H,1}-t_{H,2}
Vgross=LiWiHiV_{\mathrm{gross}}=L_iW_iH_i
Vb=Vgross−∑Vdriver−∑Vbrace−∑Vport,inside−∑VequipmentV_b=V_{\mathrm{gross}}-\sum V_{\mathrm{driver}}-\sum V_{\mathrm{brace}}-\sum V_{\mathrm{port,inside}}-\sum V_{\mathrm{equipment}}

Account for the whole internal duct

A round duct occupies its external cross-section multiplied by its length inside the cabinet. For a rectangular duct, use its external occupied cross-section. The air inside the duct belongs to the duct, not the free chamber. Do not subtract a cabinet wall twice when it also forms a slot-port wall.

Vport,inside≈π(douter2)2LinsideV_{\mathrm{port,inside}}\approx\pi\left(\frac{d_{\mathrm{outer}}}{2}\right)^2L_{\mathrm{inside}}

Worked example

A 500 x 400 x 350 mm cabinet with 18 mm panels has internal dimensions of 464 x 364 x 314 mm. Its gross internal volume is 53.03 L. Subtract 3.0 L for the driver, 1.5 L for braces, 0.8 L for electronics, and 2.85 L for the internal duct.

Vb=53.03−3.0−1.5−0.8−2.85=44.88 LV_b=53.03-3.0-1.5-0.8-2.85=44.88\ \mathrm{L}

Use 44.88 L, not 53.03 L, in the enclosure model. A changed port length also changes displacement, so a compact ported design may need another calculation pass.