Suggested enhancements for industrial silencers characterization at low frequencies

To design ventilation/air conditioning systems of collective or industrial buildings, the acoustic designers need to know with enough accuracy the performance of silencers conventionally used to treat the noise generated by the fan units. The experimental methodologies for determining acoustic attenuation is based on standards that use a reverberation room. Recent inter-laboratory comparisons showed a very large dispersion of the measured insertion loss particularly in the first frequency bands (63 and 125 Hz). Error factors are well identified: change of the modal behavior of the test duct with or without the silencer, spatial heterogeneity of the sound field in the reverberation room and sound power loss by radiation from the walls of the test duct. The Centre de Transfert de Technologie du Mans, which implements and develops a bench dedicated to the qualification of the silencers since ten years, presents in this article the results of a recent methodological study which outlines the various error factors and their influence on the measuring acoustic and aeroacoustics characteristics of industrial silencers. Based on this analysis, changes are proposed to significantly reduce low frequency error factors by using an original anechoic termination design.