Theoretical Investigation on the Sound Power Substitution Method

Sound power is a widely used acoustic quantity to characterize the emission of sound sources. It can be determined either directly or indirectly. For the latter case, the substitution method is used. This method has been chosen for the establishment of traceability in sound power determination of airborne sound. In the paper, influential parameters of the substitution method are theoretically investigated in detail and the applicability of the method is accordingly defined. A theoretical model was developed, which included the study of a number of parameters. Most importantly, in addition to sound pressure, the sound power determination was also based on sound intensity. The substitution was performed in free and hemifree field conditions, where an impedance plane was included. The required number of measurement positions and their positioning on the measuring surface were considered. Also, the effect of source position and order (monopole, dipole) on determined sound powers was investigated.