Design, optimization and validation of a small cabin for standardized objective measurements of earmuffs and earplugs on artificial head (ATF) according to ISO4869-3

The attenuation of hearing protection devices is currently mainly measured using the REAT (ISO 4869-1) standardized subjective method. However, during the development step, manufacturers need to carry out a numerous tests quickly making the REAT method unsuitable due to its need of a large number of subjects with associated training time and represents a significant cost. As an alternative, the standardized objective method (ISO 4869-3) uses an artificial head (ATF) in a controlled acoustic environment. Delta Plus called on CTTM to provide a test facility compliant with the 4869-3 standard, and designed with reduced dimensions to fit easily into its test laboratory. The presented work describes the steps of design, development and validation of a measuring cabin meeting these requirements. The search for a suitable geometry for the cabin volume is based on numerical modeling using boundary elements. The cabin, built using this initial approach, is then empirically optimized using different types of diffusers to meet sound field homogeneity criteria. Comparisons of measurements made using both subjective (ISO 4869-1) and objective (ISO 4869-3) methods are presented at the end.