Subwoofer Enclosure Designer
Calculate optimal box volume and port tuning for DIY subwoofer builds using Thiele-Small parameters.
Thiele-Small Parameters
Calculated Enclosure
Understanding Thiele-Small Parameters
The frequency at which the driver naturally resonates in free air. Lower Fs generally means deeper bass extension. Measured in Hertz (Hz).
Represents the damping of the driver. Lower Qts (0.2-0.4) suits ported boxes, higher Qts (0.4-0.7) works well in sealed enclosures.
The volume of air that has the same compliance (springiness) as the driver's suspension. Larger Vas typically requires larger enclosures.
The frequency where output drops 3dB below the reference level. This is the practical low-frequency limit of the system.
For ported enclosures, this is the frequency at which the port resonates. Lower tuning extends bass but requires longer ports.
The Q of the driver in the sealed box. 0.707 (Butterworth) gives maximally flat response. Higher values boost bass but reduce accuracy.
Calculation Formulas
Sealed Box Volume:
Vb = Vas / ((Qtc/Qts)² - 1)
Sealed F3:
F3 = Fs × √(Vas/Vb + 1)
Ported Box Volume:
Vb ≈ 15 × Vas × Qts^3.3
Port Length:
Lv = (23562.5×Dv²×N)/(Fb²×Vb) - 0.825×Dv
💡 Design Tips
- • Sealed boxes are simpler to build and offer tighter, more accurate bass with better transient response.
- • Ported boxes are more efficient and extend lower, but require precise port tuning and are larger.
- • Add 10-15% to calculated volume to account for driver displacement and bracing.
- • Use 18-25mm MDF or plywood for enclosure walls. Brace internally for rigidity.
- • Round port edges or use flared ports to reduce turbulence noise at high volumes.