Subwoofer tools.
ENCLOSURES & PORTS / THE TOOLKIT

Ported box.

Simulate complex cone and port output, cone excursion, and electrical impedance. Around tuning, the port does more of the work. Below tuning, check the cone.

01 / THE INPUTS
Driver parameters
Hz
Ω
Enclosure design
Hz
Port geometry
Drive & radiation
V
Ω

Blank uses the cone listening distance. Different paths are summed as complex pressures.

Optional acoustic losses

Leave blank for an ideal lossless port.

Leave blank for no absorption resistance.

Leave blank for an airtight chamber.

Air & conventions
m/s
kg/m3
Frequency sweep
Hz
Hz
02 / THE RESULTS
Output at tuning
107.0dB SPL
Peak cone excursion
37.27mm
10-200 Hz
Peak port air speed
27.12m/s
10-200 Hz
Driver impedance at tuning
3.59Ω

Acoustic response

LOG FREQUENCY
Acoustic response: SPL (dB) against frequency in hertz.72.8881.8190.7499.67108.6117.53102050100200SPL (dB)Frequency (Hz)

Driver excursion reaches 37.27 mm, exceeding the 12.50 mm one-way limit within this sweep. Reduce drive or evaluate protection.

Below tuning, cone excursion can rise rapidly. This small-signal estimate does not model heating, turbulence, or nonlinear driver behavior.

Read this result with its assumptions.

Sweep: 10-200 Hz, 241 logarithmic samples. Maxima describe this sampled range, not an unrestricted operating limit.

SPL is at 1 m in ideal half-space. Electrical drive is RMS; displayed excursions and air velocities are one-way peak.

Units & assumptions

Your calculations run in this browser. No account needed.

03 / UNDER THE HOOD

The math, in plain sight.

Look beyond a tuning frequency.

Build the driver and vent model

The full model uses RMS voltage drive and complex acoustic impedances. Driver parameters are derived from their small-signal relationships, with all quantities converted to SI units first.

Cms=Vasρc2Sd2,Mms=1ωs2Cms,Rms=ωsMmsQms,Bl=ωsMmsReQesC_{ms}=\frac{V_{as}}{\rho c^2S_d^2},\quad M_{ms}=\frac1{\omega_s^2C_{ms}},\quad R_{ms}=\frac{\omega_sM_{ms}}{Q_{ms}},\quad Bl=\sqrt{\frac{\omega_sM_{ms}R_e}{Q_{es}}}
Cb=Vbρc2,Lp=1(2πfb)2Cb=ρℓeffSΣC_b=\frac{V_b}{\rho c^2},\qquad L_p=\frac1{(2\pi f_b)^2C_b}=\frac{\rho\ell_{\mathrm{eff}}}{S_\Sigma}
Zp(s)=Rp+sLp,Rp=ωbLpQpZ_p(s)=R_p+sL_p,\qquad R_p=\frac{\omega_bL_p}{Q_p}

Explicit absorption and leakage model

Leaving Qa or Ql blank removes the corresponding loss. The ideal model uses Ra = 0 and infinite Rl. A modeled leak loss is not automatically an accurately modeled additional sound radiator. The default finite port Q is explicitly shown in the input form.

Yb(s)=1Ra+1/(sCb)+1Rl+1Zp(s),Zb=1YbY_b(s)=\frac1{R_a+1/(sC_b)}+\frac1{R_l}+\frac1{Z_p(s)},\qquad Z_b=\frac1{Y_b}
Ra=1ωbCbQa,Rl=QlωbCbR_a=\frac1{\omega_bC_bQ_a},\qquad R_l=\frac{Q_l}{\omega_bC_b}

Cone motion and port output

The negative chamber-pressure sign is intentional: port and cone output tend to cancel at sufficiently low frequency. The amplifier sees the displayed driver input impedance plus the external series resistance. Separate contribution curves must not be added in decibels.

Ze=Re+Rg+sLe,Zm=Rms+sMms+1sCmsZ_e=R_e+R_g+sL_e,\qquad Z_m=R_{ms}+sM_{ms}+\frac1{sC_{ms}}
v=BlEZe(Zm+Sd2Zb)+(Bl)2v=\frac{BlE}{Z_e(Z_m+S_d^2Z_b)+(Bl)^2}
Ud=Sdv,pb=−UdZb,Up=pbZpU_d=S_dv,\qquad p_b=-U_dZ_b,\qquad U_p=\frac{p_b}{Z_p}
pRMS≈∣ρsΩ(Ude−srd/crd+Upe−srp/crp)∣p_{\mathrm{RMS}}\approx\left|\frac{\rho s}{\Omega}\left(\frac{U_de^{-sr_d/c}}{r_d}+\frac{U_pe^{-sr_p/c}}{r_p}\right)\right|
Xd,peak=2∣v∣ω,Zdriver,in=Re+sLe+(Bl)2Zm+Sd2ZbX_{d,\mathrm{peak}}=\frac{\sqrt2|v|}{\omega},\qquad Z_{\mathrm{driver,in}}=R_e+sL_e+\frac{(Bl)^2}{Z_m+S_d^2Z_b}

Ideal normalized response check

This lossless, low-inductance expression is normalized to its ideal upper passband. The calculator uses the full complex model for output, cone motion, losses, and impedance.

Hreflex(s)=s4s4+ωsQtss3+[ωb2+(1+α)ωs2]s2+ωsωb2Qtss+ωs2ωb2H_{\mathrm{reflex}}(s)=\frac{s^4}{s^4+\frac{\omega_s}{Q_{ts}}s^3+[\omega_b^2+(1+\alpha)\omega_s^2]s^2+\frac{\omega_s\omega_b^2}{Q_{ts}}s+\omega_s^2\omega_b^2}
α=VasVb\alpha=\frac{V_{as}}{V_b}

Around tuning, port output can be large while cone excursion falls. Below tuning, cone excursion can rise rapidly. Check operating voltage and high-pass protection, not just the tuning frequency.