Laboratory Evaluation of Sound Pressure Levels Generated Inside the Earcups of Active Hearing Protection Devices

摘要

The purpose of this evaluation was to assess the performance of several active hearing protection devices (AHPDs) and one passive device to determine if these types of protectors are appropriate for use in a mine operator's hearing conservation program (HCP). Simultaneous noise measurements were made of the sound pressure level (SPL) inside and outside the earcup through the use of two miniature microphones. Paired SPL determinations were conducted on 11 volunteer test subjects positioned inside an anechoic test chamber while broadband test signals of varying levels were introduced. Seven earmuff-type hearing protection devices (HPDs) were evaluated-five discriminating or level-dependent types, one noise-cancellation type and one non-electronic (passive) type. The AHPDs were evaluated with their electronics set to "off," "half volume," and "full volume." The results indicated that it is possible to exceed 85.0 dB A inside the earcup of a discriminating type AHPD when the electronics are fully activated and the outside A-weighted SPL is less than 85.0 dBA. However, it is not possible to predict the external A-weighted SPL at which the AHPD's earcup internal SPL will exceed 85.0 dBA. For the five discriminating AHPDs evaluated, the range of outside SPLs that caused 85 dBA to be exceeded inside the earcup varied from a low of 82.1 dBA to a high of 109.2 dBA. There is variability among the discriminating type AHPDs when maintaining a constant internal 82 to 85 dBA SPL. This appears to be due to a combination of the electronics and the passive properties of the HPD.