Abstract
Monaural speech recognition thresholds (SRTs)for single digits of the 67-S speech audiometric test list were measured in 30 normal-hearing listeners wearing circumaural (SENNHEISER HDA 200), insert (EAR TONE 3A) or supra-aural (Rion AD-02) earphones, in order to determine the reference level for the first 2 types of earphones. The SRT of the last earphone was measured as control.
Data were collected using a within-subject design, in which each subject was tested using the different earphones, the sequence of use being counter-balanced. But, as, during the process of data analysis, a sequencing effect of lower SRTs in the second or the third measurement was partially observed, we reanalyzed the data using a between-subject design with 3 groups consisting of 10 subjects each who were tested using each earphone for the first time.
The mean SRTs in the 10 subjects for the circumaural and insert earphones were 8.9 and 9.1dBSPL, respectively, whereas the mean SRT for the supra-aural earphone was 13.7dBSPL, which almost corresponds to the 14dBSPL already established as the reference level.
When estimated from the reference internal noise spectrum levels, audible portions of the speech spectrum at the SRT levels for each earphone obtained in this study were similar, which seems to validate our results.
To establish the reference SRT levels for the two earphones, it is necessary to collect further data using an independent-group design with a larger number of test subjects and participation of test facilities.
