Hearing Threshold Shifts to High Frequency Tonal Pulses

Thirteen normal-hearing enlisted were given 11 two-hour trains of pulses at 3.5 kHz at 100 dB SPL. Acoustic load was gradually increased from one 0.5-sec pulse every 60 sec to one 0.75-sec pulse every 15 sec, at which point the group temporary threshold shift approached this Laboratorys Internal Damage Risk Criteria DRC and the experiment terminated. A very tentative and non- conservative estimate was made from these data and from the sparse literature that the ears of these men could just stand such pulses for days on end only if the SPL were reduced to 90 dB and the percentage on-time did not exceed 5. More precise DRC must wait upon rather massive data from individual subjects on the time needed for full recovery from single high-intensity pulses.