Subwoofer tools.
DRIVERS & OUTPUT / THE TOOLKIT

Thiele-Small parameters.

Enter the values you know and leave the rest blank. The solver derives every value supported by the fundamental small-signal relationships and checks redundant inputs.

01 / THE INPUTS
Driver parameters
Hz
Ω
Additional known values

Not the nominal frame diameter. Used only to calculate effective area.

N s/m
T m
Electrical damping
Ω
Air & conventions
m/s
kg/m3
02 / THE RESULTS
Total driver Q (Qts)
0.4128
Effective Qts with series resistance
0.4128
Ideal resonance impedance
41.18Ω
Moving mass
99.34g

Known, derived, and unresolved

ParameterValueUnitSource
Free-air resonance30.00HzEntered
Equivalent air volume100.00LEntered
Effective piston area500.00cm2Entered
DC resistance3.400ohmEntered
Electrical Q0.4500Entered
Mechanical Q5.0000Entered
Moving mass99.34gDerived
Suspension compliance0.2833mm/NDerived
Mechanical resistance3.7449N s/mDerived
Force factor11.894T mDerived

Read this result with its assumptions.

SI units are used internally. The consistency threshold is 2%. Nominal impedance must not be substituted for measured DC resistance.

Series-resistance Q adjustment belongs only in simplified Q-based models, not an additional adjustment to the voltage-drive model.

Units & assumptions

Your calculations run in this browser. No account needed.

03 / UNDER THE HOOD

The math, in plain sight.

Know what your driver data is telling you.

Area, compliance, and resonance

Driver specifications are interconnected. Effective piston diameter is not nominal frame diameter. Equivalent air volume expresses compliance; it is not a recommended enclosure size. The solver repeatedly applies these relationships to derive missing values.

Sd=π(deff2)2S_d=\pi\left(\frac{d_{\mathrm{eff}}}{2}\right)^2
Vas=ρc2Sd2Cms,Cms=Vasρc2Sd2V_{as}=\rho c^2S_d^2C_{ms},\qquad C_{ms}=\frac{V_{as}}{\rho c^2S_d^2}
fs=12πMmsCms,Mms=1(2πfs)2Cmsf_s=\frac{1}{2\pi\sqrt{M_{ms}C_{ms}}},\qquad M_{ms}=\frac{1}{(2\pi f_s)^2C_{ms}}

Damping and motor strength

The resonance impedance estimate assumes an unloaded, low-inductance model. Redundant relationships that differ by more than 2% are flagged; this is an input-consistency tolerance, not a claimed measurement accuracy.

ωs=2πfs,Qms=ωsMmsRms,Qes=ωsMmsRe(Bl)2\omega_s=2\pi f_s,\qquad Q_{ms}=\frac{\omega_s M_{ms}}{R_{ms}},\qquad Q_{es}=\frac{\omega_sM_{ms}R_e}{(Bl)^2}
Rms=ωsMmsQms,Bl=ωsMmsReQesR_{ms}=\frac{\omega_s M_{ms}}{Q_{ms}},\qquad Bl=\sqrt{\frac{\omega_sM_{ms}R_e}{Q_{es}}}
Qts=(1Qes+1Qms)−1=QesQmsQes+QmsQ_{ts}=\left(\frac1{Q_{es}}+\frac1{Q_{ms}}\right)^{-1}=\frac{Q_{es}Q_{ms}}{Q_{es}+Q_{ms}}
Zpeak≈Re+(Bl)2Rms=Re(1+QmsQes)Z_{\mathrm{peak}}\approx R_e+\frac{(Bl)^2}{R_{ms}}=R_e\left(1+\frac{Q_{ms}}{Q_{es}}\right)

Source and cable resistance

Qes,eff=QesRe+RgReQ_{es,\mathrm{eff}}=Q_{es}\frac{R_e+R_g}{R_e}
Qts,eff=(1Qes,eff+1Qms)−1Q_{ts,\mathrm{eff}}=\left(\frac1{Q_{es,\mathrm{eff}}}+\frac1{Q_{ms}}\right)^{-1}

Apply this only in a simplified Q-based model. The full voltage-drive model already includes source resistance in its electrical impedance. Nominal impedance is not DC resistance. Published moving mass usually includes a stated air load; adding a second radiation mass can count it twice.