1.1   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 ISO 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

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).

Additional characteristic quantities, which could in­ clude measurements taken using artificial sound sources or measurements taken to determine the di­ rectivity of sound propagation from the silencer, may be agreed upon in accordance with this International Standard.