How this calculator works
The Subwoofer Box Calculator translates driver Thiele-Small parameters (Fs, Qts, Vas) into starting sealed volume and alignment hints, plus guidance on sealed vs ported choice. Home theater and car-audio builders use it before cutting sheet goods or ordering a driver.
Sealed volume follows the classic Qtc target relation. EBP (Fs/Qts) suggests whether a vented alignment is practical. Ported boxes still need port length and panel area from the bass reflex or slot port calculators—this tool does not replace full vented modeling.
Formula used
Sealed volume: Vb = Vas / ((Qtc/Qts)² − 1). Sealed system Fc ≈ Fs × (Qtc/Qts). EBP = Fs/Qts guides enclosure type.
Example calculation
Fs = 28 Hz, Qts = 0.42, Vas = 80 L, target Qtc = 0.707: Vb ≈ 80 / ((0.707/0.42)² − 1) ≈ 25 L sealed. EBP ≈ 67 → sealed or moderate ported depending on goals.
Key terms
- Sealed box — smaller volume, controlled roll-off, higher power at resonance.
- Ported box — more output near Fb; needs correct port area and length.
- Qtc — total Q of driver plus sealed box.
- EBP — efficiency bandwidth product; higher values favor ported designs.
Frequently asked questions
- Sealed or ported for home subwoofer? Sealed for tight, accurate bass; ported for more output if the driver suits vented alignment.
- What Qtc should I target? Qtc ≈ 0.707 is a common balanced sealed starting point; lower Qtc = tighter bass.
- Does this calculate port length? No—use the bass reflex port or slot port calculator after you choose Vb and Fb.
- Why might the built sub sound different? Room gain, placement, and driver break-in change in-room response; measure and EQ if needed.