Protective Effectiveness of Earplug in Relation to Received Noise and Frequency Response of the Ear Canal

Earplug as one of the protective equipment of the auditory system has different function at different frequencies. Thus, in this study, by simulating a model of human ear canal, protective effectiveness of earplug in sound attenuation was checked at different frequencies and different lengths of the ear canal.
In this cross-sectional descriptive-analytical study, in one side of the simulated ear canal, a microphone was used as the sound receiver, and earplug was embedded in the other end of the ear canal. After playing the pink noise through the speaker, the insertion loss (IL) of earplug at one octave frequency and at different lengths of placement of earplug in simulated ear canal (12.8, 17.5, 25.5, and 31.1 mm) was examined and the results were recorded using Labview software.
Findings: The result of insertion loss of earplug at one octave frequencies showed that in comparison with other distances, the insertion loss of earplug at 25.5 mm in low frequencies (below 500 Hz) was higher, and at this distance, the frequency at 4000 Hz reached the highest rate.
The highest rate of insertion loss was achieved for low frequencies at 25.5 mm. The average length of the human ear canal is 2.5 cm; so, in human hearing system, the highest levels of environmental sound attenuation are at the this distance. Due to the maximum insertion loss of earplug at this distance and at 4000 Hz, producing protective device from absorbent substance for this frequency is suggested.