A Version of the TEN Test for Use With ER-3A Insert Earphones

Abstract

The aim of this study was to develop a version of the threshold-equalizing noise (TEN) test for the diagnosis of dead regions for use with Etymotic ER-3A insert earphones. The use of such earphones is helpful when testing clients with asymmetric hearing loss or clients whose ear canals tend to collapse under the pressure of supra-aural headphones. It can also be useful when ambient noise levels are problematic. The spectral shape of the noise required to give equal masked thresholds at all frequencies, when expressed in dB HL, was derived by empirical measurements of the electrical output of audiometers using ER-3A earphones. To reduce the loudness of the noise and to minimize distortion generated in the audiometer or earphone, the noise was band-limited between 354 and 6500 Hz. In addition, the noise was synthesized using a method that leads to a low crest factor (ratio of peak to root mean square value). This further reduced audiometer/earphone distortion, and allowed higher levels per ERBN; ERBN is the equivalent rectangular bandwidth of the auditory filter at 1 kHz, as determined using young normally hearing subjects. The test tone frequencies were limited to the range 500 to 4000 Hz. Subjects with normal or near-normal hearing were tested using a noise level of 60 dB HL/ERBN, to assess whether the noise did lead to equal masked thresholds in dB HL for all audiometric frequencies from 500 to 4000 Hz. Thresholds in the TEN were measured using manual audiometry with a 2 dB final step size. The mean-masked thresholds varied by 1.3 dB across frequency when expressed in dB HL, and were close to the noise level per ERBN. This version of the TEN test can be used with ER-3A insert earphones.