Influence of insertion depth of an insert earphone on hearing threshold levels and on real ear attenuation values

Abstract

The influence on pure-tone hearing threshold levels (HTLs) of the insertion depth of the coupling foam eartip of EARTONE™ 3A insert audiometric earphones was investigated in 16 subjects using three distinctly different insertion depths: shallow, intermediate, and full. HTLs were also measured using conventional earphones, model TDH-50P with MX/41-AR cushions. In addition, sound field real ear at threshold (REAT) values re: ANSI S12.6-1984 were recorded in each condition. The results showed that there was a tendency toward poorer HTLs as the eartip was positioned further away from the eardrum, with the difference between the three widely disparate insertion depths amounting to 1.3–5.3 dB in the frequency range 0.5–6 kHz. In contrast, at 8 kHz, significantly less (8.1 dB) energy was required for elicitation of threshold response in the shallow position as compared to the two other. However, no statistically significant differences were found between the most appropriate (full and intermediate) insertion depths at any tested frequency. Although REAT values showed increased attenuation for the frequencies 0.125–1 kHz as the eartip was inserted more deeply in the ear canal, at all three insertion depths over all tested frequencies, values were more than 15 dB greater than the attenuation obtained with the conventional earphone.