Observations on the correlation of subjective and objective attenuation measurements on earplugs

Real-ear attenuation at threshold (REAT) has been recognized as the gold-standard method to evaluate the attenuation of hearing protection devices (HPDs). The question is often posed as to whether or not REAT measurements could be replaced with objective, insertion loss (IL) measurements conducted on acoustical test fixtures for assessing the performance and consistency of HPDs. To understand how IL data correspond to REAT data for earplugs, both methods were used to assess three earplugs. The resulting data were compared, and the HPD attenuation ranked at each frequency. In most cases, after correction for bone conduction limits, occlusion effect, and physiological noise, IL data show good agreement with REAT values. Discrepancies at some frequencies were found and varied by HPD. The IL data did not identify the high standard deviation of the REAT results on one earplug. The IL data did not correspond well to the REAT values, resulting in differences as large as 12 dB at some frequencies. In conclusion, IL and REAT procedures are used for different purposes when assessing attenuation characteristics of HPDs. While close agreement was found at most frequencies, IL data may not reflect the REAT performance of HPDs equivalently in all aspects.