Comparison of hearing thresholds measured with supra-aural headphones and earphones fitted to custm earmoulds

An investigation to compare hearing threshold levels measured with headphones (THP) and button-type earphones (TEP) was performed with eight moderately-to-profoundly hearing-impaired adults. The earphone output was calibrated in this study by measuring the sound pressure level using an ear simulator (B and K Type 4157). The earphone threshold levels were combined with the reference equivalent threshold SP Ls for the ER -3A insert earphone (ANSI, 1989) to convert the earphone data to equivalent dB HL units. Differences in threshold levels for headphones and earphones (THP – TEP) were within 5 dB for frequencies between 125 Hz and 2000 Hz, except at 1414 Hz where it was +8.7dB. At 2828 and 4000 Hz, the differences were −10.4 and −19.6 dB, respectively. Random variance in measured threshold levels was comparable for earphones and headphones in the frequency range of 125–2828 Hz. The results of this study have established a set of correction figures enabling the calibration of hearing threshold levels measured via the Oticon AN1000 earphone into equivalent dB HL units. These data are now being used in a computer-assisted hearing-aid fitting procedure to improve the accuracy and reliability of hearing-aid fitting for hearing-impaired individuals, while eliminating the need to measure thresholds separately using an audiometer and headphones.