Hearing aid measurements using the revised standard: reducing variability and determining test system accuracy

Unlike previous standards, the revised hearing aid standard, (ANSI S3.22-1976), specifies tolerance requirements for the electroacoustic characteristics of hearing aids. It is essential, therefore, that measurements of performance be made as accurately as possible. To assess the precision with which these measures can be made in a clinical environment, five hearing aids of the same model were each tested five times using Bruel and Kjaer instrumentation. When possible, data were recorded directly from the meter of the measuring amplifier as well as from the chart paper. The variability of the results was always less when data were obtained from the meter than from the chart. The ratio of the variability(meter:chart) differed depending on the test being made. The accuracy of the test system was derived (as required by the standard) both theoretically and empirically. When its estimated tolerances wee added to the tolerances permitted for the aids, all hearing aids were found to perform well within the limits of the standard except for one measurement on one aid.