Subwoofer Box Calculator & Speaker Enclosure Designer

Sealed and vented alignments

Following Leach’s Audio Engineering Formula Sheet (pp. 1–2), recover electrical Q as $Q_{es}=Q_{ms}Q_{ts}/(Q_{ms}-Q_{ts})$ and include series resistance through $Q'_{es}=Q_{es}(R_e+R_g)/R_e$. Combine $Q'_{es}$ with $Q_{ms}$ to obtain effective total Q.

For a sealed box, $\alpha_s=V_{as}/V_b$, $f_c=f_s\sqrt{1+\alpha_s}$ and $Q_{tc}=Q'_{ts}\sqrt{1+\alpha_s}$. Target-Q sizing inverts this relation. The sealed F3 is the half-power frequency of its second-order high-pass.

For the vented model let $z=jf/f_s$, $h=f_b/f_s$, $B=z^2+hz/Q_L+h^2$, and $D=(z^2+z/Q'_{ts}+1)B+\alpha_v z^2$. The normalized pressure response is $G_v=z^4/D$. QL represents lumped enclosure leakage; absorption and port losses are not separate parameters. Automatic sizing interpolates the original 179-row Leach QL = 7 table for compliance and tuning ratios. F3 is solved from $|G_v|^2=1/2$ using the highest low-frequency crossing, excluding the active filter and cabin overlay.

Travel, port and cabinet

Derive $C_{ms}=V_{as}/(\rho c^2S_d^2)$, $M_{ms}=1/(\omega_s^2C_{ms})$, and $Bl=\sqrt{\omega_sM_{ms}R_e/Q_{es}}$. Peak force is $Bl\sqrt{2}V_{rms}/(R_e+R_g)$ and $x_0=F_{pk}/(M_{ms}\omega_s^2)$. Cone travel is $x_0/(z^2+z/Q'_{ts}+1+\alpha_s)$ sealed or $x_0B/D$ vented. Port speed follows volume continuity: $u_p=-\omega_sS_dx_0h^2z/(S_pD)$. The optional Butterworth high-pass multiplies these complex transfer functions.

Leach’s round-port relation is $L_p=(c/(2\pi f_b))^2S_p/V_b-1.463r_p$, for one flanged and one free end. Port length includes the baffle. Gross internal volume adds net airspace, driver/bracing displacement and the portion of the tube inside the cabinet, including its air column and tube wall.

The cabin overlay adds $\min(G_{cap},\max(0,g\log_2(f_{cab}/f)))$ dB. This is an explicitly chosen scenario, not an inferred vehicle measurement.

Band maxima are refined continuously with bounded optimization around all local peaks of a logarithmic scan seeded by the system’s damped modal frequencies. Both band endpoints are candidates. Cone-travel and port-speed warnings and power limits use these refined maxima. Each refined peak and nearby points are also inserted into the plotted frequency axis.

One driver, a rigid airtight sealed box or a vented box with lumped leakage, fixed small-signal parameters and constant amplifier source voltage. The source voltage is defined before series resistance. Air uses Leach’s reference values, c = 345 m/s and ρ = 1.18 kg/m³.

Sealed absorption losses, changed air loading, stuffing and voice-coil inductance are omitted. The vented pressure response uses the conventional fourth-order lumped-loss approximation. Port velocity and cone travel are peak values; Xmax is one-way peak. The demonstration uses complex steady-state displacement and a slowed display cycle. The section drawing is schematic.

Cabinet planning assumes one straight front-mounted round tube, one flanged and one free end, uniform panels, and user-supplied driver/bracing displacement. The port’s interior air column is excluded from the enclosure compliance volume. The default driver is generic. The schematic amplifies travel and caps its display range for clarity; use the numeric peaks to assess Xmax.

Use below the driver’s piston/breakup range and below port pipe resonances. A 241-point logarithmic scan is augmented by modal frequencies, continuous peak refinement and endpoint checks. The plots include the refined maxima; a narrow resonance may require zooming to inspect its shape. No claim is made about frequencies outside the study band. Bare-box F3 excludes the protective filter and cabin gain.

Automatic vented sizing requires effective Qts between 0.1704707 and 0.6819966 and assumes QL = 7. Use manual mode and measured losses for refinement. Measure tuning after construction; end geometry and nearby walls change it.

Excursion- and airflow-limited power references do not include thermal limits, clipping, distortion or nonlinear compression. KICKER’s approximate Mach 0.1 upper guideline is only a screening threshold; lower velocity and suitable flares may be needed for quiet operation. Cabin gain is an adjustable overlay, not an acoustic model of a particular car.

Cabinet dimensions are volume planning, not a cut list or structural assessment. Check driver frame/cutout, mounting depth, bracing and front-panel layout from actual drawings. Full passive crossover design is outside this tool; enter its series resistance if relevant.

Validation is applied separately to the selected enclosure and its comparison. An invalid selected design blocks results. An invalid comparison is omitted from the plots and its output cards say Unavailable; the selected design, dimensions and motion remain usable.