The ear is most easily damaged between 3 and 8 kHz

Evidence

For 100 subjects, each with normal hearing, the solid curve in Fig. 2.3 indicates the median threshold of hearing. In addition to that 50% curve, data are given that encompass 10% and 90% of the subjects’ individual thresholds in quiet. Thresholds below the 90% curve are usually accepted as normal. The difference between the 90% curve and the 10% curve is small for medium frequencies. Towards low and higher frequencies this difference increases. In discussing this difference, it is remarkable that the 90% curve does not follow the 50% curve in the frequency range between 3 and 8 kHz, rather it increases in the range where the 50% curve decreases. It may be that a small percentage of the young subjects already exhibit a small hearing loss in the frequency range around 4 kHz. This result points to the fact that our hearing system is most easily damaged in the frequency range between 3 and 8 kHz if it is exposed to loud sounds above the limit of damage risk. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 170