Theory

Every frequency of the sweep is an independent solve of the Helmholtz equation (one factorisation of the system matrix).

Linear spacing: the frequencies run from $f_{min}$ in steps of Frequency step, equation (1).
Logarithmic spacing: Number of frequencies (logarithmic) frequencies are spaced evenly in $\log f$ between $f_{min}$ and $f_{max}$ , equation (2).
Octave, 1/3-octave or custom spacing: the field is locked and shows the lowest solved frequency, i.e. the lower edge of the first band or the first listed frequency.

At very low frequency the muffler is acoustically compact and its transmission loss depends mainly on the port areas. The solve is inexpensive there, and because the sound field changes slowly with frequency, a coarse step is sufficient.

Equations

f_j = f_{min} + j\,\Delta f, \qquad j = 0, 1, \ldots,\ \text{while } f_j \le f_{max}

(1)

f_j = f_{min}\left(\frac{f_{max}}{f_{min}}\right)^{j/(n-1)}, \qquad j = 0, \ldots, n-1

(2)

where	meaning	unit
$f_j$	Solved frequencies	Hz
$f_{min}, f_{max}$	Lowest and highest frequency	Hz
$\Delta f$	Frequency step (linear)	Hz
$n$	Number of frequencies (logarithmic)	-

Default and rule

Default: 20 Hz
Rule: 20 Hz.
Source: The frequency list is the program's own construction.

Valid range > 0 and < f_max; set by the band range or the list for octave, 1/3-octave and custom spacing

Values

Above 0 and below $f_{max}$ .

Theory

Equations

Default and rule

Valid range > 0 and < f_max; set by the band range or the list for octave, 1/3-octave and custom spacing

Related 4