This International Standard specifies methods for determining – the insertion loss, in frequency bands, of ducted silencers with and without airflow, – the sound power level, in frequency bands, of the flow noise (or regenerated sound) generated by ducted silencers, – the total pressure loss of silencers with airflow, and – the transmission loss, in frequency bands, of air-terminal units. The measurement procedures are intended for laboratory measurements at ambient temperature. Measurements on silencers in situ are specified in ISO 11820. It is to be noted that the results determined in a laboratory according to this International Standard will not necessarily be the same as those obtained in situ (installation), as different sound and flow fields will yield different results. For example, the pressure loss will be lower under laboratory conditions than in situ, but will be comparable between different laboratories. This International Standard is applicable to all types of silencer including silencers for ventilating and airconditioning systems, air intake and exhaust of flue gases, and similar applications. Other passive air-handling devices, such as bends, air-terminal units or T-connectors, can also be tested using this International Standard. This International Standard is not applicable to reactive silencers used for motor vehicles. NOTE 1 – Annex A specifies the sound field excitation equipment. Annex B gives requirements for the transition element. Annex C gives details of duct walls and limiting insertion loss. Annex D specifies how to convert one-third-octave band attentuation values to octave band values. Annex E gives requirements for measurements on large parallel-baffle silencers. Annex F specifies a test of longitudinal attenuation. Annex G gives guidelines on anechoic terminations and Annex H shows examples of measurement arrangements. NOTE 2 – Acoustic testing of air-terminal devices and fan-coil units is to be carried out as described for air-terminal units. NOTE 3 – Sound power measurements on air-terminal units are specified in ISO 5135. Measurements of the pressure loss of air-terminal units are described in EN 12238, EN 12239 and EN 12589.