Subwoofer tools.
ENCLOSURES & PORTS / THE TOOLKIT

Port air velocity.

Use the complete driver-and-box model, or an isolated-port SPL estimate near tuning. A port diameter alone cannot tell you whether a design will be quiet.

01 / THE INPUTS
Model selection
Port output
dB
Hz
Port geometry
Air & conventions
m/s
kg/m3
02 / THE RESULTS
Peak air velocity per port
10.00m/s
RMS air velocity per port
7.07m/s
Peak Mach number
0.0292
Peak air-particle displacement
53.07mm

Constant 100 dB isolated-port output

LOG FREQUENCY
Constant 100 dB isolated-port output: Peak air speed (m/s) against frequency in hertz.06.4812.9619.4525.9332.41102050100200Peak air speed (m/s)Frequency (Hz)

Port-only, far-field estimate. Do not use it where cone output is significant, or with a near-field SPL reading.

Read this result with its assumptions.

Mach number is not a universal chuffing threshold. The sweep assumes the same isolated-port SPL at every frequency, not the response of a real enclosure.

Units & assumptions

Your calculations run in this browser. No account needed.

03 / UNDER THE HOOD

The math, in plain sight.

Check the air speed your vent must carry.

From the coupled driver-and-box model

The full-system mode uses the driver, compliance, vent, and cone-velocity equations published in the ported-box calculator. For N identical ports, divide their combined RMS volume-velocity phasor equally.

Up,1=Up,ΣN,vRMS,1=∣Up,1∣S1U_{p,1}=\frac{U_{p,\Sigma}}N,\quad v_{\mathrm{RMS},1}=\frac{|U_{p,1}|}{S_1}
vpeak,1=2∣Up,Σ∣NS1,Machpeak=vpeak,1cv_{\mathrm{peak},1}=\frac{\sqrt2|U_{p,\Sigma}|}{NS_1},\qquad\mathrm{Mach}_{\mathrm{peak}}=\frac{v_{\mathrm{peak},1}}c
ξpeak=vpeak,12πf\xi_{\mathrm{peak}}=\frac{v_{\mathrm{peak},1}}{2\pi f}

From an isolated-port SPL target

This shortcut applies only when a compact port provides approximately all the radiated sound at the chosen frequency. Enter a far-field SPL, not a near-field microphone reading.

pRMS=20×10−6 10Lp/20 Pap_{\mathrm{RMS}}=20\times10^{-6}\,10^{L_p/20}\ \mathrm{Pa}
∣Up,Σ∣≈ΩrpRMSρ 2πf|U_{p,\Sigma}|\approx\frac{\Omega r p_{\mathrm{RMS}}}{\rho\,2\pi f}
vpeak,1≈2 ΩrpRMSρ 2πf NS1v_{\mathrm{peak},1}\approx\frac{\sqrt2\,\Omega r p_{\mathrm{RMS}}}{\rho\,2\pi f\,NS_1}

In ideal half-space at 1 m, 100 dB from one 100 mm port at 30 Hz implies approximately 10 m/s peak velocity under the port-only assumption.

A comparison measure, not a universal threshold

Mach number is not a universal chuffing limit. Flares, adjacent walls, port shape, turbulence, and the program signal matter. Increasing area lowers speed at a given flow, but generally requires a longer port at the same tuning.

The isolated-port sweep holds the entered SPL constant at every plotted frequency. It is not a predicted frequency response of a real enclosure.