ÖNORM EN ISO 11820

1 .l This International Standard specifies measurements on silencers in situ. It is applicable to measurements on silencers in practical applications for acoustic analysis, acceptance tests and similar evaluations. Results obtained in accordance with this International Standard cannot be compared to performance data obtained from laboratory measurements on ducted silencers in accordance with IS0 7235, partly because of different test conditions (such as sound field distribution, flow, temperature and mounting conditions) and partly because of different definitions. Depending on the method used, the measurement is either of - insertion loss Dis, or - transmission loss Dt,. The measurement method depends upon the type of silencer and the installation conditions (e.g. insertion loss measurements must be carried out for blowdown silencers). NOTE 1 The subscripts denote the practical application of the silencer and the particular installation and operating conditions: s stands for ¿I situ, t for transmission, and i for insertion. Additional characteristic quantities, which could include measurements taken using artificial sound sources or measurements taken to determine the directivity of sound propagation from the silencer, may be agreed upon in accordance with this International Standard. 1.2 This International Standard is applicable to a) silencers which are installed either as a whole or in the form of individual baffles in the propagation path of sound (e.g. openings of ducts) originating from a sound source (machine, building, plant