Double hearing protectors (DHPs), earplugs and earmuffs worn in combination, may be needed in high level noise environments. The DHP sound attenuation is known to be less than the sum of each single protector attenuation. This effect, referred to as the DHP effect, is still not fully understood. A recent study has shown that it can be observed on an acoustic test fixture (ATF) and characterized by the decrease of the earplug noise reduction (NR) when the earmuff is added. In this paper, a measurement methodology is proposed to (i) identify the main sound paths related to the DHP effect on an ATF and (ii) explain the latter by the relative contributions of the air-borne and structure-borne transmissions in the system. The focus is put on the NR values of the earplug alone and in the DHP. Measurement results suggest that the DHP effect is related to the energy transmitted from the earcup, through the earmuff cushion and finally into the earcanal via the sound radiation of the earplug and/or earcanal lateral walls. This flanking structure-borne path is found to dominate over the “direct” air-borne path through the hearing protectors at frequencies above 300 Hz.

在高噪声环境中，可能需要组合使用双耳保护器（DHP），耳塞和耳罩。已知DHP声音衰减小于每个单个保护器衰减的总和。仍未完全了解这种效应，称为DHP效应。最近的一项研究表明，可以在声学测试装置（ATF）上观察到它，并且其特征在于，添加耳罩后，耳塞的噪音降低（NR）降低。在本文中，提出了一种测量方法，用于（i）确定与DHP对ATF的影响有关的主要声路，以及（ii）通过系统中空中和结构传播的相对贡献来解释后者。 。重点放在单独的耳塞和DHP中的NR值上。测量结果表明，DHP效应与从耳杯，通过耳罩垫并最终通过耳塞和/​​或耳道侧壁的声辐射进入耳道的能量有关。发现在频率高于300 Hz时，这种侧向的结构传播路径在通过听力保护器的“直接”空中传播路径中占主导地位。