Source quantity

Theory

With an SWL, the program converts power to pressure at the microphone using hemispherical radiation over a reflecting ground ($Q = 2$), spherical spreading and air absorption, equation (1).

With an SPL, no conversion from power is made: the measured level already contains the radiation of the reference pipe at the distance $d_s$ (Source measurement distance). The program subtracts the insertion loss and transfers the level from $d_s$ to the microphone distance $d$, equation (2). The ground factor is the same at both distances and cancels.

The SPL form requires no assumption about the power and directivity of the source, because the measured reference condition contains them. In SPL mode the radiated sound power level is not computed (left blank in spl.csv), and the divergence and absorption columns hold the change from $d_s$ to $d$.

Equations

Default and rule

Default

swl

Rule

swl.

Source

The SPL form is defined by the program; the SWL form follows $L = L_W + D_c - A$ of ISO 9613-2. A-weighting of the outputs: (IEC 61672-1, 2013).

Valid range swl (sound power level) | spl (sound pressure level)

Related 3

• Calculate radiated SPLacoustics.radiated_spl.enabled
• Source measurement distanceacoustics.radiated_spl.source_distance
• Microphone distanceacoustics.radiated_spl.distance

References 1

1. International Electrotechnical Commission (2013). Electroacoustics - Sound level meters - Part 1: Specifications. IEC 61672-1:2013. Web page