DPOAE level mapping for detecting noise-induced cochlear damage from short-duration music exposures

Distortion product otoacoustic emission (DPOAE) level mapping provides a comprehensive picture of cochlear responses over a range of DP frequencies and f2 /f1 ratios. We hypothesized that individuals exposed to high-level sound would show changes detectable by DPOAE mapping, but not apparent on a standard DP-gram. Thirteen normal hearing subjects were studied before and after attending music concerts. Pure-tone audiometry (500-8,000 Hz), DP-grams (0.3-10 kHz) at 1.22 ratio, and DPOAE level maps were collected prior to, as soon as possible after, and the day after the concerts. All maps covered the range of 2,000-6,000 Hz in DP frequency and from 1.3 to -1.3 in ratio using equi-level primary tone stimuli. Changes in the pure-tone audiogram were significant (P ≤ 0.01) immediately after the concert at 1,000 Hz, 4,000 Hz, and 6,000 Hz. The DP-gram showed significant differences only at f2 = 4,066 (P = 0.01) and f2 = 4,348 (P = 0.04). The postconcert changes were readily apparent both visually and statistically (P ≤ 0.01) on the mean DP level maps, and remained statistically significantly different from baseline the day after noise exposure although no significant changes from baseline were seen on the DP-gram or audiogram the day after exposure. Although both the DP-gram and audiogram showed recovery by the next day, the average DPOAE level maps remained significantly different from baseline. The mapping data showed changes in the cochlea that were not detected from the DP-gram obtained at a single ratio. DPOAE level mapping provides comprehensive information on subtle cochlear responses, which may offer advantages for studying and tracking noise-induced hearing loss (NIHL)

The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

<p><i>Objective:</i> This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. <i>Design:</i> The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. <i>Results:</i> The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB <i>L</i>_Aeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. <i>Conclusions:</i> Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.</p