The document specifies methods for the determination of the acoustical performance of silencers under various installation conditions (e.g. in ducts, at openings, in walls). Measurement quantities are sound pressure levels in third-octave bands or octave bands upstream and downstream from the silencer (for transmission loss measurements) or with and without the silencer (for insert in loss measurements). In addition, dynamic pressures, flow velocities and temperatures are measured at various points. Particular sound field distributions and extraneous sound are accounted for through corrections. The test report contains the acoustical loss D and the corrections applied as well as a schematic description of the installation conditions according to a specified scheme.