Normal hearing threshold levels in the low-frequency range determined by an insert earphone.

Hearing threshold levels have been determined in the low-frequency range (20-500 Hz) on a group of 30 young normal-hearing subjects using monaural stimulus presentation through an insert earphone (Etymotic Research ER-3A). A retest was performed on half of the group to provide data on test-retest reliability. The mean hearing threshold levels obtained agree closely with the Minimum Audible Field data of ISO 226, however, with some deviation at the very lowest frequencies below 40 Hz. The test-retest difference results yielded mean values that averaged 1.15 dB with an average standard deviation across test frequencies of 3.9 dB. The results show that low-frequency hearing thresholds for pure tones of frequencies from 40 Hz and up can be determined with acceptable validity and reliability by the use of this type of insert earphone.