Idota Nozomi, Horie Seichi, Tsutsui Takao, Inoue Jinro
Department of Health Policy and Management, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan.
J UOEH. 2002 Mar 1;24(1):11-8. doi: 10.7888/juoeh.24.11.
The attenuation characteristics of the earplug using a dummy head (KEMAR; Knowles Electronics Manikin for Acoustic Research) were measured, when it was exposed to pure tones or broadband noises at three different sound pressure levels (SPLs) of 70, 80 and 90 dB SPL in the 'wide frequency range from 250 to 20 k Hz. We ascertained the satisfactory capacity of noise attenuation except for from 10 k to 14 k Hz. The noise attenuation level increased with frequency until 2 k Hz, became almost constant until 8 k Hz, then decreased at around 10 k to 14 k Hz, and recovered in the range from 16 k to 20 k Hz. The frequency characteristics were identical among three different sound pressure levels and almost identical between pure tones and broadband noises. The change of frequency characteristics affected by the depth of the earplug that was inserted into the artificial ear canal of the KEMAR was also investigated. Measured sound pressure level by the builetin microphone in the KEMAR revealed a region in which the measured sound pressure levels were relatively higher around 10 k Hz. The frequency of the region moved higher when the earplug was inserted more deeply. Therefore it was considered that this phenomenon was related to the resonance frequency of the cylinder-like cavity made between the end section of the earplug and the diaphragm of the built-in microphone.
使用仿真人头（KEMAR；用于声学研究的Knowles电子人体模型）测量了耳塞在250至20 kHz的宽频率范围内暴露于70、80和90 dB SPL三种不同声压级的纯音或宽带噪声时的衰减特性。我们确定了除10 kHz至14 kHz外令人满意的噪声衰减能力。噪声衰减水平在2 kHz之前随频率增加，在8 kHz之前几乎保持恒定，然后在10 kHz至14 kHz左右下降，并在16 kHz至20 kHz范围内恢复。三种不同声压级的频率特性相同，纯音和宽带噪声之间几乎相同。还研究了插入KEMAR人工耳道的耳塞深度对频率特性变化的影响。KEMAR中内置麦克风测得的声压级显示，在10 kHz左右存在一个测量声压级相对较高的区域。当耳塞插入更深时，该区域的频率会升高。因此，认为这种现象与耳塞末端与内置麦克风振膜之间形成的圆柱状腔体的共振频率有关。
