Observation on Protective Effect of Hearing Protectors on Infrasound.

Objective To observe the sound attenuation effect of several kinds of hearing protectors (earplugs and earmuffs) in an infrasound generator sound field. Method Using a real time analyzer (Type 840 made in Norway), linear sound pressure level (dBSPL), sound level (dBA), infrasound level and 1/3 octave band sound pressure level (4～20 000 Hz) were measured on an artificial head (B.K. Type 4128) under two conditions: with or without hearing protectors (i.e. naked and closed ear). The difference between sound pressure levels, sound levels, and infrasound levels under the two conditions was designated as sound attenuation values. Result The sound attenuation values of 3 types of earplug tested were: 16.4～19.4 dB for infrasound level, 20.0～21.6 dB and 23.0～25.6 dBA for linear sound pressure level and sound level, respectively. When 2 types of earmuff were used, the sound attenuation values for infrasound level were 0.4 and -0.3 dB, for linear sound pressure level were 7.2 and 3.2 dB, and for sound level were 22.4 and 19.5 dBA, respectively. It suggested that there was no hearing protection to infrasound. When a combination of earmuff and earplug was used, the protection to infrasound and low frequency sound showed no additive effect. It indicated that sound attenuation was mainly dependent on the earplug, but for middle and high frequency sound the additive effect was significant. Conclusion The results indicate that earplugs provide more effective protection against infrasound exposure than earmuffs.