Temporary Threshold Shifts of Sounds with Equal A-Weighted Levels

Project Details


Traditional sound exposure assessment methods use the A-weighting function to give frequency dependent significance to the components of the exposure. It is thereby assumed that exposures that have the same equivalent A-weighted sound pressure level will pose the same risk of damage to the auditory system. In order to investigate this premise, the effect of sound exposures with the same equivalent A-weighted sound pressure levels but different frequency contents was evaluated through a temporal threshold shift (TTS) experiment. A recording of an industrial mill was made in a workshop. The recordings were post-processed so that three 2-octave band signals centered at 250 Hz, 1 kHz and 4 kHz were constructed. The signals were adjusted to have the same equivalent A-weighted level, and used as fatiguing stimuli in a threshold shift experiment including nine subjects. The results show that the high band produced the greatest threshold shift, spreading over a greater frequency range, and with a longer recovery period. The 2-octave band centered at 1 kHz also produced TTS, while the band centered at 250 Hz did not produce any TTS of significance. Analysis of the results through a stochastic model (see project "Temporary threshold shifts due to short tonal over-exposure"), confirms the observations on the results. In conclusion, this project has shown some evidence that contradicts the assumption that exposures with the same A-weighted level pose the same risk for the hearing, considering TTS as an early indicator of possible noise induced hearing loss. Supported by STVF/FTP.
Effective start/end date19/05/201031/12/2017