What is ISO 11691 about?
ISO 11691 discusses acoustics for measuring the insertion loss of ducted silencers without flow.
ISO 11691 specifies the laboratory substitution method that is used to determine the insertion loss without the flow of ducted, mainly absorbent, circular, and rectangular silencers as well as other duct elements for use in ventilating and air-conditioning systems.
ISO 11691 applies to silencers where the design velocity does not exceed 15 m/s and circular silencers with diameters of 80mm to 200mm or for rectangular silencers with cross-sectional areas within the same range.
Note 1: ISO 11691 does not cover silencers where the type of noise is of great importance for the evaluation of the silencer performance because the method does not include self-generated flow noise.
Who is ISO 11691 for?
ISO 11691 on measurement of insertion loss is relevant to:
- Air-conditioning system manufacturers
- Air-conditioning systems suppliers
- Manufacturers and suppliers of silencers
- Research laboratories
Why should you use ISO 11691?
Airflow does not affect the insertion loss of ducted silencers if the flow velocity does not exceed approximately 20m/s in the narrowest section of silencers. The velocity limit of 20m/s corresponds to a design velocity of 10 m/s to 15 m/s.
Different sounds and flow fields also often lead to different results due to which the insertion loss determined is not necessarily the same as the insertion loss obtained in an installation in the field.
Methods mentioned under ISO 11691 assist in measuring the insertion loss of ducted silencers and thus, guide in manufacturing efficient silencers for ventilating and air-conditioning systems.
ISO 11691 assists in evaluating the performance of your silencers which thus, helps in manufacturing other products of high quality which uses silences.
What’s changed since the last update?
BS EN ISO 11691:2020 supersedes BS EN ISO 11691:2009 which is withdrawn. The main changes are:
- Insertion of a modal filter after the source
- Test ducts and test objects should, if possible, have the same cross-sections in this document
