Sealed speaker box calculator
Set the net volume and see Qtc, resonance frequency Fc and −3 dB point of the selected driver at once. A Qtc of about 0.7 is the Butterworth (maximally flat) alignment; lower sounds tight, higher adds a bump.
Try it free in the app
Formulas
Qtc = Qts · √(1 + Vas/Vb) and Fc = Fs · √(1 + Vas/Vb). A smaller volume raises Fc and Qtc.
Choosing Qtc
0.5–0.6: very tight and well damped, needs more volume; 0.7: maximally flat; above 0.9: noticeable hump (“boomy”). Near a wall a slightly lower Qtc is often pleasant.
Frequently asked questions
What volume does a sealed box need?
For Qtc 0.707: Vb = Vas / ((0.707/Qts)² − 1). The calculator shows the result in the response curve as you move the slider.
What does Qtc mean?
The total Q of driver and box at Fc. It decides whether bass sounds tight (low) or boomy (high).
Does it apply with damping material?
Stuffing slightly increases the effective volume and damps cabinet modes. The app accounts for it; this calculator assumes an empty box.