Observations upon the Relationship of Loudness Discomfort Level and Auditory Fatigue to Sound-Pressure Level and Sensation Level

Studies carried out upon subjects with normal hearing have shown that (a) the mean sound-pressure level at which a tone of 1000 Hz is judged to be unpleasantly loud is 100 dB and (b) following sustained stimulation with intensities above 100 dB, there occurs a dramatic increase in the resultant temporary threshold shift. The intensity at which both these events occur is independent of sensation level. It follows that variations in normal threshold of the order of ±10 dB are largely sensorineural in orgin. In addition, the fact that both these unrelated events occur at the same sound-pressure level suggests that it marks a physiological limit of loudness perception. The results lead to the conclusion that the loudness function shows considerable intersubject variability and is dependent upon hearing acuity. Their application to loudness computations and to hearing conservation is discussed.