Use this tool to estimate a sealed box volume from Thiele/Small parameters and compute a vented port length for a target tuning. Values are practical starting points for DIY subwoofer and woofer cabinet design.
Sealed Enclosure Inputs
Vented Port Inputs
Port length uses a common round-port approximation and includes one end correction term. Real-world testing is still recommended.
How this loudspeaker enclosure calculator helps
A cabinet can make or break a speaker system. The same driver in the wrong box can sound boomy, weak, or muddy. In the right box, it can sound controlled, deep, and natural. This calculator gives you quick estimates for two common design paths:
- Sealed (acoustic suspension) box volume from Fs, Qts, Vas, and desired Qtc.
- Vented (bass reflex) round-port length from box volume, tuning frequency, and port size.
These are practical estimates intended for DIY planning and prototyping. They are not a replacement for full simulation and measurement, but they are excellent for first-pass design decisions.
Input parameters explained
Fs (Hz)
The driver's free-air resonant frequency. Lower Fs generally supports deeper bass potential, assuming sufficient displacement and enclosure size.
Qts
Total Q of the driver in free air. It helps determine how strongly the driver is damped and has major influence on sealed box sizing and alignment behavior.
Vas (liters)
An equivalent compliance volume describing suspension softness. Larger Vas often means the driver “wants” a larger enclosure for similar system behavior.
Qtc
The target system Q for sealed alignments. A common target is 0.707 (Butterworth-like response). Lower values can sound tighter but may need bigger boxes; higher values can increase mid-bass emphasis.
Vb, Fb, and port dimensions
For vented designs, you choose the net box volume and desired tuning frequency, then solve for port length. Port diameter and port count strongly affect required length and potential turbulence (“chuffing”).
Formulas used in this page
Practical build tips
- Use net volume: subtract driver displacement, bracing, terminal cup, and port volume from gross internal volume.
- Plan bracing early: stiffer cabinets reduce panel resonance and improve clarity.
- Mind port length: very long ports may require bends, slot ports, or passive radiators.
- Test and verify: a quick impedance sweep confirms real tuning frequency and catches build errors.
- Control leaks: sealed systems especially depend on airtight construction.
Sealed vs vented: quick decision guide
Choose sealed if you want:
- Smaller cabinet sizes
- Smoother roll-off and simpler build
- Excellent transient response
Choose vented if you want:
- More low-frequency output near tuning
- Higher efficiency in the bass region
- Better extension from a given driver (with proper design)
Important note
This calculator provides engineering approximations. Real driver behavior depends on box losses, stuffing, temperature, excursion limits, room gain, and manufacturing tolerances. For final designs, validate with simulation software and measurements before committing to production cuts.