Theory

Diameters are always those of the circle of equal AREA, equation (1), so a non-circular port becomes a round pipe of the same area. A branch with the area of its own inlet makes the incident power of a given pressure amplitude the same in the pipe as in the muffler, equation (2), so both are driven identically. On auto the trunk (and with it the outlet) has the diameter of the largest inlet; a typed diameter changes the trunk only (with one inlet, the whole pipe).

Equations

D = \sqrt{\frac{4A}{\pi}}

(1)

W_{inc} = \frac{\lvert A_p\rvert^2 S}{2\rho c}

(2)

where	meaning	unit
$D$	Equivalent diameter	m
$A$	Area of the port	m²
$W_{inc}$	Incident plane-wave power at an inlet	W
$A_p$	Incident pressure amplitude	Pa
$S$	Inlet area	m²
$\rho, c$	Density and speed of sound	kg/m³, m/s

Default and rule

Default: auto: circle of the area of the largest inletComputed by the program
Rule: Auto: the equivalent diameter of the largest inlet.
Source: The reference pipe is the program's own construction. The plane-wave power is the modal power of the port model.

Valid range > 0

Values

Above 0, or auto.

Different inlet gases

The pipe has one uniform gas, that of the largest inlet; a note and a warning appear when the characteristic impedances of the inlets differ by more than 1 %.

Theory

Equations

Default and rule

Valid range > 0

Related 3