Subwoofer tools.
ENCLOSURES & PORTS / THE TOOLKIT

Sixth-order bandpass.

Choose two external ports (parallel) or an interchamber port and a front external port (series). Complex pressures, not decibel levels, are added together.

01 / THE INPUTS
Driver parameters
Hz
Ω
Enclosure design
Hz
Hz

Sets acoustic port mass using the rear chamber alone, not the coupled system tuning.

Port geometry
Drive & radiation
V
Ω
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
Peak sampled output
116.9dB SPL
Lower -3 dB edge
36.66Hz
Upper -3 dB edge
77.56Hz
Peak cone excursion
38.34mm
10-200 Hz

Acoustic response

LOG FREQUENCY
Acoustic response: SPL (dB) against frequency in hertz.70.4580.4490.42100.41110.4120.39102050100200SPL (dB)Frequency (Hz)

Driver excursion reaches 38.34 mm, exceeding the 12.50 mm one-way limit within this sweep. Reduce drive or evaluate protection.

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.

Passband edges enclose the largest sampled peak and use a reference 3 dB below that peak. Other lobes or a narrow peak are not a broad, flat passband.

Units & assumptions

Your calculations run in this browser. No account needed.

03 / UNDER THE HOOD

The math, in plain sight.

Different layouts need different models.

Common driver and chamber model

Sixth-order bandpass describes more than one topology. The calculator keeps two external ports and the series interchamber layout separate. A chamber-only reference tuning defines port mass; it is not a guarantee of the coupled system tuning.

Ci=Viρc2,Zpi=Rpi+sLpi,Lpi=1(2πfbi)2CiC_i=\frac{V_i}{\rho c^2},\quad Z_{pi}=R_{pi}+sL_{pi},\quad L_{pi}=\frac1{(2\pi f_{bi})^2C_i}
YF=sCF,YR=sCR,Zm=Rms+sMms+1sCms,Ze=Re+Rg+sLeY_F=sC_F,\quad Y_R=sC_R,\quad Z_m=R_{ms}+sM_{ms}+\frac1{sC_{ms}},\quad Z_e=R_e+R_g+sL_e
v=BlEZe[Zm+Sd2Zload]+Bl2,Ud=Sdvv=\frac{BlE}{Z_e[Z_m+S_d^2Z_{\mathrm{load}}]+Bl^2},\qquad U_d=S_dv

Optional absorption and leakage use the explicit chamber model on the ported-box page, referenced to each chamber-only tuning. Port Q sets Rp = omega_b Lp / Qp. Driver properties follow the Thiele-Small relationships.

Parallel: one external port from each chamber

YEF=1ZpF,YER=1ZpR,pF=UdYF+YEF,pR=−UdYR+YERY_{EF}=\frac1{Z_{pF}},\quad Y_{ER}=\frac1{Z_{pR}},\quad p_F=\frac{U_d}{Y_F+Y_{EF}},\quad p_R=-\frac{U_d}{Y_R+Y_{ER}}
Zload=1YF+YEF+1YR+YERZ_{\mathrm{load}}=\frac1{Y_F+Y_{EF}}+\frac1{Y_R+Y_{ER}}
UF=YEFpF,UR=YERpRU_F=Y_{EF}p_F,\qquad U_R=Y_{ER}p_R

Add complex radiating pressures, not separate decibel levels. Identical ideal chamber-and-port halves can cancel acoustically when their propagation paths are the same.

Series: one internal port, one external port

YI=1ZpI,YE=1ZpEY_I=\frac1{Z_{pI}},\qquad Y_E=\frac1{Z_{pE}}
[YF+YE+YI−YI−YIYR+YI][pFpR]=[Ud−Ud]\begin{bmatrix}Y_F+Y_E+Y_I&-Y_I\\-Y_I&Y_R+Y_I\end{bmatrix}\begin{bmatrix}p_F\\p_R\end{bmatrix}=\begin{bmatrix}U_d\\-U_d\end{bmatrix}
D=(YF+YE+YI)(YR+YI)−YI2D=(Y_F+Y_E+Y_I)(Y_R+Y_I)-Y_I^2
pF=YRUdD,pR=−(YF+YE)UdD,Zload=YF+YE+YRD,Uexternal=YEpFp_F=\frac{Y_RU_d}{D},\quad p_R=-\frac{(Y_F+Y_E)U_d}{D},\quad Z_{\mathrm{load}}=\frac{Y_F+Y_E+Y_R}{D},\quad U_{\mathrm{external}}=Y_Ep_F

Pressure, excursion, and impedance

p~total≈ρsΩ∑jUje−srj/crj\widetilde p_{\mathrm{total}}\approx\frac{\rho s}{\Omega}\sum_j\frac{U_je^{-sr_j/c}}{r_j}
Xd,peak=2∣v∣ω,Zdriver,in=Re+sLe+Bl2Zm+Sd2ZloadX_{d,\mathrm{peak}}=\frac{\sqrt2|v|}{\omega},\quad Z_{\mathrm{driver,in}}=R_e+sL_e+\frac{Bl^2}{Z_m+S_d^2Z_{\mathrm{load}}}

These are small-signal lumped-chamber models. High internal pressure and narrow responses warrant prototyping and measurement. The plots include separate contributions only for outlets that radiate externally.