[Effectiveness of ear protective devices]

Efficiency of 9 types of hearing protectors was investigated. A subjective method of an absolute hearing threshold shift in free sound field in 20 well-hearing-persons was applied. The results obtained are presented in figures. It was found that the maximum efficiency of most hearing protectors usually fell toon the frequency of 4000 Hz and amounted to 20--41 dB. The minimum efficiency usually fell to the frequency of 125 Hz and amounted to 8--21 dB. Attenuation efficiency of broad-band noise was 18-40 dB and approximated the maximum efficiency of pure sounds, sometimes even surpassing it. The results of determinations differed from the values given by manufacturers, which accounts for the need of undertaking such investigations.