Abstract
In 308 ears which cleary showed noise-induced impariment, the continuous audiometry was made by using a Békésy type audiometer. On the continuous audiogram, the dip didn't always appear at 4KHz and the dip at 5KHz was found as frequent as at 4KHz. In most ears, the extent of hearing loss to the lower frequency range was limited to 2.5KHz and very few ears with marked hearing loss extending over the frequency limit of 2KHz were proved only of the long term workers. It has already been agreed generally that the threshold at 8KHz is so much unstable and is markedly affected with age-factor.
To the profound noise deafness or the aged workers, the fourfold division method has a danger of underor overestimating the individual hearing level of noise deafness. Then, it is better to exclude the threshold at 2 and 8KHz for taking the avarage of hearing level in noise deafness.
In order to evaluate the hearing level of noise deafness exactly, the mean value of threshold at 3, 4, 5, and 6KHz is rather serviceable to prevent of miscalculating the hearing level in noise deafness than the so-called fourfold division method.
