Abstract
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 20k Hz. We ascertained the satisfactory capacity of noise attenuation except for from 10k to 14k Hz. The noise attenuation level increased with frequency until 2k Hz, became almost constant until 8k Hz, then decreased at around 10k to 14k Hz, and recovered in the range from 16k to 20k 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 built-in microphone in the KEMAR revealed a region in which the measured sound pressure levels were relatively higher around 10k Hz. The freguency 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.
