A comparison of attenuation measurement methods of active noise reduction earmuffs

Abstract

Active noise reduction (ANR) devices have become increasingly popular in recent years. It is important to evaluate the noise reduction performance of ANR devices correctly and efficiently. Because the procedure specified in ISO 4869-6 is time-consuming, a more efficient, accurate procedure is needed. In this study, three subjective and objective attenuation measurement methods are investigated: real-ear attenuation at threshold (REAT), microphone-in-real-ear (MIRE), and acoustic test fixture (ATF). Several results follow. First, the MIRE method is suitable for passive, active, and total attenuation measurements when the attenuation is well below the bone conduction limits. Additionally, compared to using the lowest attenuation of the two ears, averaging the attenuation of the left and right ears measured by the MIRE method is closer to the REAT results. Next, due to physiological noise masking under the ANR-off condition, the procedure specified in ISO 4869-6 may greatly overestimate the noise reduction performance of ANR earmuffs at low frequencies. Finally, the active attenuation measured on the artificial ear consisting of an IEC 60711 occluded-ear simulator and a pinna does not always correspond well to measurements of test subjects.