Evaluation of the Zwislocki coupler and KEMAR for use in hearing-aid processing

A calibrated-probe-tube technique was employed in a comparative investigation of the real-ear frequency response of a hearing aid and the real-ear response as processed through the hearing aid and two coupler systems. The swept-tone output of the aid was delivered to a Zwislocki coupler, and later to one eat of the manikin KEMAR [M. D. Burkhard and R. M. Sachs, J. Acoust. Soc. Am. 58, 214–222 (1975)], which housed the same Zwislocki coupler. Outputs were recorded on magnetic tape and subsequently transduced by a TDH-49 earphone. Resultant sound levels were measured in the right ear canal of 11 subjects. Conventional frequency responses were also measured utilizing the two coupler systems. The acoustic input channel and input monitoring point were held constant under each condition. Responses of both coupler systems paralleled closely the live, real-ear, response of the aid. Minor and major differences were observed in the lower and higher frequencies, respectively, between hearing-aid-processed and real-ear sound levels.