Threshold shifts and restitution of the hearing after energy-equivalent noise exposures with an equal NRC-value and non-equal frequency composition

摘要

Based on industrial noise, test noise exposures were configured that were completely comparable in the sense that they all had a mean level of 94 dB(A) for 1 h and a Noise Rating Curve-value of 92, but for two of them, the band levels were increased in the lower frequency range and in the higher frequency range of the industrial noise, respectively, with compensating attenuation in the other frequency ranges. Ten otologically normal test subjects were exposed to the 3 noises which followed a change-over test design on 3 days. The maximum threshold shift TTS_2 and the time needed for a complete recovery of the hearing, associated with the accented high-frequency noise were substantially higher and lasted longer than with the unaltered original industrial noise. The accented low-frequency noise also resulted in substantially higher threshold shifts that persisted for a longer time than those of the unaltered noise exposure. As a result, the Integrated Restitution Temporary Threshold Shifts (IRTTS), known as measure for the "Physiological Costs" in their entirety that the hearing must "pay" for the preceding noise exposures, different very distinctly. Finally, when the IRTTS-values of the two test series with the altered spectra are expressed relative to the value for the original industrial noise, the quotients of 5.26 and 1.99 indicate substantially higher physiological responses associated with accented high-frequency and low-frequency components in energetically identical noise exposures.