This standard describes methods of accuracy grade 2 (engineering grade) for determining the sound power level and sound energy level of a noise source (machinery or equipment) from sound pressure levels measured on a surface enveloping the noise source. For this purpose the noise source under test shall be installed in an environment that approximates to an acoustic free field near one or more reflecting planes. Amongst others, requirements are specified for the test environment, instrumentation, measurement surfaces and installation and operation of the noise source under test. The qualification procedures for the acoustic environment, microphone arrays on the various measurement surfaces and the determination of the sound power and sound energy levels under meteorological reference conditions are described in annexes. Another annex contains a guideline on the development of information on measurement uncertainty. The most important alterations with respect to the 2009 edition of the standard are as follows: a) absolute criterion for background noise has been additionally added; b) maximum permissible environmental correction has been increased from 2 dB to 4 dB; c) determination of sound energy levels has been added; d) treatment of measurement uncertainty has been extended and approach in accordance with the GUM Guide has been added; e) for the determination of the environmental correction based on the room absorption the absorption area can also be determined with a with a reference sound source; f) new, preferred microphone positions on the hemispherical measurement surface for all noise sources (broadband and tonal) have been additionally specified; g) specifications for microphone arrays on a quarter-hemispherical measurement surface (position of the noise source in a corner) have been added; h) alternative microphone arrays on the parallelepiped measurement surface have been added; i) specifications for microphone arrays on a cylindrical measurement surface have been added; j) annex with an alternative microphone array on the hemispherical measurement surface (in accordance with ISO 4872:1978) - especially for direct measurements of A-weighted sound pressure levels and moving noise sources - has been added; k) annex for the determination of sound power and sound energy levels under meteorological reference conditions has been added; l) annex with guidelines on the development of information on measurement uncertainty has been added; m) standard has been editorially revised. The international standard on which this standard is based has been prepared by Working Group 28 "Basic machinery noise emission standards" of ISO/TC 43/SC 1 "Noise" with German participation. On the European level the standard exists within the framework of CEN/TC 211 "Acoustics". Regarding German cooperation, the responsible Working Committee is NA 001-01-04 AA "Geräuschemission von Maschinen und Anlagen: Messung, Minderung, Datensammlung" ("Noise emission of machines and plants: measurement, reduction, data collection") of NALS.