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This report from the National Center for Health Statistics presents data on the characteristics of three different configurations of Telephonics TDH-39 audiometer earphones and of a newer design, the TDH-49 earphone, as determined by loudness balance on 12 human subjects. The TDH-39 earphones were ones used for determining auditory threshold in the Health Examination Surveys of 1963 to 1965.
The audiometers used in these surveys were all calibrated on standard couplers in terms of the sound pressure at auditory threshold for people with normal unimpaired hearing as defined by the 1951 American Standard reference values. However, these reference values had been fairly rigorously determined only for the Western Electric 705-A audiometer earphone and other types of earphones which were no longer commercially available at the start of the Health Examination Survey. The corresponding reference values for the audiometer earphones used in the surveys had been determined only in part at
National Center for Health Statistics. Vital and Health Statistics. Arch Otolaryngol. 1971;93(5):545. doi:10.1001/archotol.1971.00770060791029
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