During the last few decades it has appeared that noise deafness is characterized by a hearing loss which is mainly restricted to the high frequencies. In the audiogram such a hearing loss manifests itself in a so-called dip, which is generally called the c5-dip. This term c5-dip finds its origin in the use of tuning forks and of discontinuous or octave audiometry for audiological examinations. For if the hearing loss is determined at the octave-spaced frequencies 125, 250, 500, 1,000, 2,000, 4,000, and 8,000 cps and an increased threshold value is found at 4,000 cps, the threshold values at 2,000 and 8,000 cps being normal or nearly normal, a c5-dip has been determined per definition. It is very well possible, however, that the greatest hearing loss occurs at a frequency which lies between 2,000 and 4,000 or between 4,000 and 8,000 cps. In such
GRAVENDEEL DW, PLOMP R. The Relation Between Permanent and Temporary Noise Dips. AMA Arch Otolaryngol. 1959;69(6):714–719. doi:10.1001/archotol.1959.00730030728009
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