ISO 11691:2020 outlines a laboratory substitution method for determining the insertion loss of ducted, primarily absorbent, circular and rectangular silencers, as well as other duct components used in ventilation and air-conditioning systems.
Note: Laboratory measurement procedures for ducted silencers with superimposed flow are detailed in ISO 7235.
This method applies to silencers with a design velocity not exceeding 15 m/s. Since the method does not account for self-generated flow noise, it is not suitable for testing silencers where this type of noise significantly impacts performance evaluation. Given that most silencers, especially in office and residential settings, operate at design velocities below 15 m/s, this document often serves as a cost-effective alternative to ISO 7235.
It is important to note that the insertion loss measured in the laboratory may not reflect the insertion loss experienced in actual field installations, as varying sound and flow conditions in the duct can lead to different outcomes. In this document, the sound field is primarily influenced by plane wave modes. The use of standardized test ducts may also introduce some flanking transmission through structural vibrations in the duct walls, which can limit the maximum insertion loss that can be measured.
This document is specifically designed for circular silencers with diameters ranging from 80 mm to 2,000 mm, as well as for rectangular silencers with corresponding cross-sectional areas within the same range.
