Assessment of insert earphones for the use in occupational hearing conservation program monitoring audiometry

The application of insert earphones for annual audiometry was evaluated in an on-going occupational hearing conservation program. For four consecutive years employees were given an extra left-ear audiogram using a 3A-type insert earphone immediately after completing their standard annual audiograms using TDH-49 earphones in supra-aural cushions. For the final 3 yr an additional left-ear audiogram using the TDH-49 earphone was given last, to control for order effects. Sixty employees participated all 4 yr. Analysis of thresholds obtained each year using each earphone indicated that small threshold correction factors for the insert earphone are necessary at each frequency (not just at 6 and 8 kHz) to allow results to be compared directly to supra-aural earphone thresholds. The manufacturer's suggested 10-dB correction factor at 8 kHz appeared too small for the particular combination of TDH-49 and insert earphones used. Standard deviations of thresholds between individuals were similar for both earphones. Year-to-year repeatability of thresholds within individuals was equivalent with both earphones. As long as absolute calibration is accounted for, insert earphones are a viable alternative transducer for audiometry in hearing conservation.