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of sensory hearing loss seem to be reversible. For

Another characteristic type of audiogram found in sensory hearing loss is shown in Fig. 10.8. This is sometimes described as a C-5 dip, and in this instance the cause was exposure to intense noise. It is the serial audiogram of a man who was exposed to extensive small-arms gunfire, with the result that he suffered a permanent high-frequency loss. It is appropriate to point out that the term "C-5 dip" is not very satisfactory. It is commonly designated this way because of the manner in which audiograms are done. If the tests were to be made at several hundred Hertz on either side of 4000 Hz, the so-called C-5, the chances are that the dip would be found there as well. When testing is done with continuous-frequency audiometry, the dips can occur at 3000Hz, at 5000 or 6000Hz, or anywhere in between, without involving 4000Hz. Consequently, the term "C-5 dip" should be replaced by the term "high-frequency dip," which really means that the hearing is relatively normal on either side of a sharp depression in the hearing level.