Experimental Study on Ear Defenders

Abstract

The effects of ear defenders have been experimentally investigated. Seven kinds of various defenders were used in this experiment. The methods and results are as follows: 1. The intensity of sound transmitted through the ear defender was measured in the sound proof room with the artificial ear. In this experiment, the artificial ear constituted of an acoustic coupler and a condenser microphone was set in front of the speaker. The sound from the speaker was controlled by an automatic device. From the result, the ear defenders are divided into two groups; the one is the group which is effective only in the higher frequencies, while another in all auditory frequencies. 2. The auditory threshold for pure tones was measured when one was applied with or without the ear defender. Five healthy men were employed as objects. The objects sat down at the distance of one meter from the speaker. The variation of auditory threshold when wearing the ear defender are the same, notwithstanding the types of defenders. That is, the elevation of threshold are only 20-30db in the frequency range higher than 1000 cps. 3. Recruitment phenomena are positive in masked ears by the thermal noise, but negative in ones with defenders. 4 The ears masked by the thermal noise, and that with the defenders, have recruitment phenomenon, but this phenomenon is weaker than in case of just masked ears.