Theoretical considerations on the sound power substitution method
* Presenting author
The acoustic emission of sound sources is characterised today by the sound power. In practice, the assumption of independent sound power from the outer sound field, is frequency limited for sufficiently broad frequency bands. To extend the validity of the current measurement procedures, the characterization of a sound source based on its free-field sound power is proposed. The basic tool for this proposal is the establishment of traceability for the free-field sound power. The implementation of the traceability chain includes the substitution method. By this approach the measured and really existing field quantities, could be referred to the field quantities that would exist in case of free field conditions.The contribution discusses a theoretical study focusing on the factors that influence the substitution method according to numerical calculations for sound pressure and sound intensity. Reflecting planes have been considered and the mirror source approach has been implemented for both plane and spherical waves. The effects imposed by the translation of the source under investigation and by the reflecting plane impedance has also been studied. The influence of the measurement surface has also been investigated along with that imposed by the numerical settings, which dictate the computational power needed.