Our ducted attenuator test rig is a UKAS accredited facility for testing to BS EN ISO 7235:2009 “Laboratory measurement for ducted silencers and air-terminal units insertion loss, flow noise, and total pressure loss”.
This standard has been around for a while although it has not been widely adopted until recently. SRL is the only independent laboratory that is UKAS accredited to this standard. This standard uses a significantly different approach to earlier test standards, in particular, the latest standard now includes a “modal filter” to create a predominantly “plane wave” sound field. This change means that the results obtained under BS EN ISO 7235:2009 can be very different from the old BS 4718 standard and we have seen attenuators where the differences are greater than 10dB. Although BS 4718 was withdrawn in 2003, many attenuators on the market still quote performances based on tests to this standard but, be aware that, if you are selecting attenuators or your existing data is from testing to the old standard, you risk inaccuracies and as a consequence, the system may fail to meet the required specification.