Theory

The source SPL already contains the radiation of the reference pipe at $d_s$ . The program subtracts the insertion loss and transfers the level from $d_s$ to the microphone distance $d$ , equation (1): the correction is the change in spherical spreading and in air absorption between the two distances. With $d_s = d$ the result is simply the source SPL minus the insertion loss.

Equations

L_p = L_{p,src} - IL - 20\lg\frac{d}{d_s} - \alpha\,(d - d_s)

(1)

where	meaning	unit
$L_{p,src}$	Source SPL at $d_s$	dB
$IL$	Insertion loss	dB
$d$	Microphone distance	m
$d_s$	Source measurement distance (this setting)	m
$\alpha$	Atmospheric attenuation coefficient	dB/m

Default and rule

Default: 0.5 m
Rule: 0.5 m (the same as the default microphone distance).
Source: The distance correction is the program's own, built from the spreading and absorption terms of the point-source model.

Valid range 0 < d_s ≤ 100 m; source quantity SPL only

Values

Above 0, at most 100 m. Shown only when the source quantity is SPL.

Theory

Equations

Default and rule

Valid range 0 < d_s ≤ 100 m; source quantity SPL only

Related 3