Audio Intensity Free Enclosure Tools
Subwoofer box calculator suite by Audio Intensity
Free Tools · Built by an IASCA / MECA SQ Champion

Subwoofer Box Calculator Suite

Design a subwoofer enclosure the right way. Model sealed response with a live graph, calculate port length, and check displacement — then jump to our specialized airspace, EBP, port-area, and tuning tools.

Sealed DesignerPorted / Port LengthDisplacementAll 6 ToolsReference Charts
Quick answer: A subwoofer box calculator sizes an enclosure to your driver’s Thiele–Small parameters. Use EBP to choose sealed vs ported, the sealed designer below to model volume and response, and the port length + area tools to finish a ported build.

Sealed Enclosure Designer

Enter your driver’s Thiele–Small parameters and your box volume to compute Qtc, Fc, and predicted frequency response.

Qtc, Fc & frequency response

Load an example driver:
–Qtc
–Fc (Hz)
–Box ratio (Vas/Vb)
–−3 dB (Hz)

Frequency Response (relative SPL, normalized)

Your boxCompare

Optimal Vb Targets — click a row to load it

Alignment Qtc Vb Fc −3 dB Character
Calculate to see suggested alignments for this driver.
Formula reference
Box ratio (a) a = Vas / Vb
System Q Qtc = Qts × √(a + 1)
System resonance Fc = Fs × √(a + 1)
−3 dB point solved from |H(f)| = 1/√2
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Ported Box & Port Length Calculator

Enter net box volume, target tuning, and port shape to get port length. For high-excursion drivers, verify velocity in the Port Area tool.

Port length for target tuning (Fb)

–Port length (in)
–Port length (cm)
–Total port area (in²)

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Displacement → Gross Volume Helper

Calculators give net volume. The box you build must be bigger to make up for the driver, port, and bracing. This adds it back.

Net + displacement = gross build volume

–Gross (ft³)
–Gross (L)
–Added (ft³)

Build to the gross volume; once the driver, port, and bracing are in, you land on your net target.

Your Full Specialized Tool Set

Six dedicated calculators for every stage of a build.

1

Decide the alignment

EBP tells you sealed or ported.

2

Set the airspace

Net volume, either path.

3

Take your path

Sealed design, or port area if ported.

4

Dial the tuning

Ported only. Sets the final Fb.

5

Wire it up

Voice coils to final amp impedance.

EBP calculator: sealed vs ported decision
Step 1 · Decide

EBP Calculator

Efficiency Bandwidth Product from Fs and Qes — sealed or ported.

Open EBP Calculator
Subwoofer airspace calculator
Step 2 · Volume

Airspace Calculator

Recommended internal airspace so the enclosure matches the driver.

Open Airspace Calculator
Sealed box calculator
Step 3 · Sealed path

Sealed Box Calculator

The standalone full sealed-design tool with deeper options.

Open Sealed Box Calculator
Subwoofer port area calculator
Step 3 · Ported path

Port Area Calculator

Sizes port area for high-excursion subs so airflow stays quiet.

Open Port Area Calculator
Subwoofer tuning tool
Ported path

Subwoofer Tuning Tool

Find your real Fb, or set the target tuning to build toward.

Open Tuning Tool
Subwoofer power handling calculator: cone excursion versus Xmax in a sealed enclosure
Step 4 · Verify

Power Handling Calculator

Cone excursion vs Xmax in your sealed box — how much power it can safely take at every frequency.

Open Power Handling Calculator
Subwoofer wiring diagram generator
Step 5 · Wiring

Wiring Diagram Generator

Voice coil configuration to final impedance, with the diagram to follow.

Open Wiring Generator
Subwoofer enclosure design guide
Learn

Enclosure Design Guide

The full written guide behind these tools.

Read the Guide

Reference Charts

Handy tables for box design. Free to reference — a link back to this page is appreciated.

Sealed Box Qtc: What Each Value Does

Qtc Alignment Box size Best for
0.577 Bessel — best transient Largest Reference SQ
0.707 Butterworth — flattest Large Sound quality
0.8–0.9 Slight peak, punchy Medium Daily / SQL
1.0+ Peaky, boomy Small Tight spaces

Qtc must be higher than the driver’s Qts. Lower Qtc = bigger box + deeper extension.

EBP: Sealed or Ported?

EBP (Fs ÷ Qes) Suits
Below ~50 Sealed enclosure
~50–100 Either — size vs output
Above ~100 Ported enclosure

A quick starting guide, not an absolute rule.

Port Air Velocity Targets

Peak velocity Result
Under ~17 m/s Clean — good SQ target
~17–30 m/s Usually OK for SPL
Above ~30 m/s Chuffing likely — add area

~5% of the speed of sound (~17 m/s) is a common clean target.

Common Round Port Areas

Diameter Area (in²) Area (cm²)
2 in 3.1 20.3
3 in 7.1 45.6
4 in 12.6 81.1
6 in 28.3 182.4

Start around 12–16 in² of port per cubic foot; high-excursion subs want more.

What You’ll Need: Thiele–Small Parameters

Every calculator here runs on your subwoofer’s spec sheet.

Fs — free-air resonant frequency (Hz).
Qts — total Q; drives sealed-vs-ported suitability.
Qes — electrical Q; used with Fs for EBP.
Vas — equivalent compliance (L or ft³).
Xmax — linear excursion (mm); matters for port sizing.
Sd — cone area; used with Xmax for displacement.

Bought your sub from us? Send the model and we’ll pull the parameters for you.

Rather We Just Build It?

We CNC-cut Proline X enclosures to your driver’s exact net target on ShopSabre routers — sealed or ported, spec-matched, built in Tennessee.

Shop Proline X Enclosures Read the Enclosure Design Guide

Subwoofer Box Calculator FAQ

How do I calculate the right subwoofer box size?
Use your driver’s Thiele–Small parameters. For a sealed box, enter Qts, Fs, Vas, and your box volume and the designer returns Qtc, Fc, and the response curve. For ported, set net volume and target tuning, then size the port. Always add back the volume the driver, port, and bracing displace.
What is the best Qtc for a sealed subwoofer box?
0.707 (Butterworth) is the flattest, most accurate response and the usual sound-quality choice. 0.577 (Bessel) has the best transient response but needs a bigger box; 0.8–1.0 shrink the box and add punch with a peak. The graph lets you compare them.
How do I calculate port length for a ported box?
Port length depends on net box volume, target tuning (Fb), and total port area. Enter those in the ported calculator and it returns the length. More port area or a lower tuning both need a longer port.
Should I build a sealed or ported box?
Sealed is smaller, tighter, and more accurate; ported is louder and deeper but needs more space and tuning. Run the EBP calculator — below ~50 favors sealed, above ~100 favors ported.
What is net vs gross box volume?
Net is the air the driver actually sees; gross is the raw internal volume before the driver, port, and bracing take up space. Build to a larger gross volume — the displacement helper adds it back.
Do you build the enclosure for me?
Yes. Once you know your target volume and tuning, we CNC-cut a Proline X enclosure to that exact net spec in Tennessee — sealed or ported, matched to your driver.
Audio Intensity Free subwoofer enclosure calculators · Audio Intensity, Tullahoma TN

Subwoofer box calculators by Audio Intensity.