References: Measurement microphones - Part 1: Specifications for laboratory standard microphones IEC Publication, , 61094-1; Measurement microphones - Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique IEC Publication, , 61094-2; (2010) Acoustics - Determination of Sound Power Levels and Sound Energy Levels of Noise Sources Using Sound Pressure - Precision Methods for Reverberation Test Rooms, , International Standard, ISO 3741, Fourth Edition; (2010) Acoustics - Determination of Sound Power Levels and Sound Energy Levels of Noise Sources Using Sound Pressure - Engineering Methods for an Essentially Free Field over a Reflecting Plane, , International Standard, ISO 3744, Third Edition; (2012) Acoustics - Determination of Sound Power Levels and Sound Energy Levels of Noise Sources Using Sound Pressure- Precision Methods for Anechoic Rooms and Hemi- Anechoic Rooms, , International Standard, ISO 3745, Third Edition; Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Intensity. Measurement at Discrete Points, , International Standard, ISO 9614-1:2009; Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Intensity. Measurement by Scanning, , International Standard, ISO 9614-2:1997; Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Intensity. Precision Method for Measurement by Scanning, , International Standard, ISO 9614-3:2009; Hübner, G., Eine Betrachtung zur Physik der Schallabstrahlung (1991) Acustica, 75, pp. 130-144. , in German; Völkel, K., Schmelzer, M., Guglielmone, C., Arina, R., Wittstock, V., Analytical study on the sound field generated by a baffled vibrating structure (2013) JRP SIB 56 Report, , Deliverable 1.1, Germany; Kirbaş, C., Bilgiç, E., Körük, H., Belek, H.T., Sadikoǧlu, E., Karaböce, B., Velocity distribution measured on the primary source by TÜBİTAK UME and ITU JRP SIB56 Sound Pwr Report, , Deliverable 1.2.6, Turkey; Cellard, P., Andersson, H., Brezas, S., Wittstock, V., Automatic sound field sampling mechanisms to disseminate the unit watt in airborne sound (2016) Internoise, , Hamburg; August; (2000) Acoustics - Requirements for the Performance and Calibration of Reference Sound Sources Used for the Determination of Sound Power Levels, , International Standard, ISO 6926, Corrected Second Edition

At present, airborne sound power is not a directly measurable quantity. It is calculated from sound pressure measurements performed in special environments, e.g. free or diffuse fields or from sound intensity measurements using 2-microphone probes. All the different methods are lacking traceability and transparent uncertainty budgets. These deficiencies are finally based on the lack of a primary standard for sound power as the metrological basis. In the joint research project funded by the European Metrology Research Program, primary sound power standards were established on the base of the Rayleigh Integral Method where the sound power is calculated from measured velocities on a baffled vibrating body. Different reference sound power sources were designed in different Institutes. The construction of the primary sources was mainly focused on the piston; its material, shape and friction during its movement. Primary sound power sources were installed in hemi anechoic and reverberant environments, and characterisation measurements were performed to see the effect of different environments on the sound power output. Comparison measurements were performed to compare the new and present methods for the primary sound power source.