Select Your DriverPick a subwoofer from our database or enter your own Thiele-Small parameters.
Choose Enclosure TypeCompare sealed and ported (vented) box designs side by side.
Tune & See ResultsAdjust box volume, power, and port tuning. See SPL frequency response update in real time.
FEATURES
Sealed & ported enclosure modeling
Real-time SPL frequency response graph (10β500 Hz)
Xmax excursion limit visualization
Port dimension calculator β round, slot, and aeroport
Port air velocity warnings
Power handling limit warnings
Imperial & metric unit toggle
Free, no signup, no install β runs in your browser
What Is a Subwoofer Box Calculator?
A subwoofer enclosure calculator uses Thiele-Small parameters β Fs, Qts, Vas, Xmax and others β to predict how a driver will perform in a given box. The enclosure type and dimensions dramatically affect bass response. The same subwoofer can sound boomy, tight, or flat depending on the box.
This tool models both sealed (acoustic suspension) and ported (bass reflex) enclosures. Sealed boxes offer smooth, predictable roll-off. Ported boxes extend bass response lower but require careful port tuning to avoid noise and cone unloading.
Whether you're building a car audio subwoofer box, a home theater sealed sub, or a DIY speaker project β this calculator helps you find the right box volume and tuning before you cut wood.
Fs--
Qts--
Xmax--
Vas--
Tap to change driver βΊ
Box Volume
VOLβQTC
-- L
VβW
-- V
β
Port Tuning
-- Hz
ΓβArea
--
Count
Port Ends
Width8 cm
Height4 cm
Walls
Between two parallel surfaces
Size
Count
Port Ends
Γ--
SPL RESPONSE
π
Impedance graph
coming soon
SELECT DRIVER
CUSTOM DRIVER
Series = 2ΓRvc, Parallel = Β½Rvc. Enter Re and Bl for the final wired configuration.
W
The maximum continuous RMS power the driver can handle without damage. Found on the datasheet. Not the peak or "music power" rating.
How far the cone can travel in one direction before distorting. This is one-way β if the datasheet says "peak-to-peak", divide by 2.
Γ DiameterβSd β piston area
β Sd: β
The effective moving diameter of the cone. Measure from the middle of the surround on one side to the middle of the surround on the other side.
β Γ: β
The effective radiating area of the cone. Usually listed on the datasheet. Used to calculate how much air the driver moves.
Hz
The frequency at which the driver's cone naturally wants to vibrate in free air β like a pendulum frequency. A lower Fs generally means better bass extension potential. Required to calculate anything else.
The volume of air that has the same springiness as the driver's suspension. A larger Vas means a more compliant (floppy) suspension. Critical for calculating the ideal box volume.
β Vas: β (needs Fs + Sd)
Total moving mass β the cone, voice coil, former, and the small amount of air that moves with it. Heavier cones tend toward deeper bass but lower sensitivity.
Q & Motor Parameters
β
Electrical Q factor β describes how strongly the motor (voice coil in magnet field) controls the cone's movement. Lower Qes = stronger motor grip. Typically 0.3β0.8 for subwoofers. Listed on every datasheet.
β Bl: β (auto-calculated when Fs + Mms + Re are known)
β
Mechanical Q factor β how much the suspension (spider + surround) and internal friction damp the cone. Higher Qms means less mechanical loss. Usually 3β10 for subwoofers.
β
Total Q factor β the single most important parameter for choosing box type. Qts < 0.4 β sealed, 0.4β0.7 β ported, > 0.7 β free-air or large vented. Auto-calculated when both Qes and Qms are entered above.
dB
β enter Qes above for auto-calculated sensitivity
How loud the driver is at 1 metre with 1 watt of power. Auto-calculated from Fs + Vas + Qes β often more accurate than the manufacturer spec. You can also type the datasheet value directly.