An Examination of the Occurrences of Metaphor in Introductory Engineering Textbooks

Custom-designed hearing instruments comprise the majority of those dispensed in the United States today. Because of their custom nature, there has been no means of evaluating them until they have been completed. There would be advantages to evaluating custom instruments prior to their completion. This study investigates a means of evaluating custom instruments prior to their final assembly into the customized shell. This is done by having the subject listen to the circuitry of the instrument while it is still mounted on the faceplate, which is accomplished by coupling the faceplate assembly to the subject's ear with foam earplug. To determine if the faceplate assembly, when coupled to the subject's ear, is a facsimile of the completed instrument, the insertion gain of the faceplate assembly was compared to the insertion gain of the completed instrument. Real ear measurements were obtained for both conditions (faceplate assembly vs. custom instrument) on twelve subjects. Once insertion gain was measured, the faceplate assemblies were then converted into custom instruments and insertion gain remeasured. A two-way Analysis of Variance test revealed no significant difference between the two test conditions at five representative test frequencies. A tolerance template, as specified by ANSI S3.22 1982, was used as a second criterion for similarity between two conditions. The tolerance template was superimposed over the insertion gain curves of the twelve faceplate assembly conditions to determine if the insertion gain curves of the completed instrument fell within acceptable variances. None of the insertion gain curves for the completed instruments fell completely within the tolerances allowed by the template. Based on this criterion, it was concluded there was a significant difference between the insertion gain of the two conditions and therefore the faceplate assembly was not a facsimile of the completed instrument, where insertion gain was concerned. However, from a subjective standpoint the faceplate assembly might still have some utility in the fitting of the custom in-the-ear hearing instruments. For example, it could be used to allow potential hearing aid wearers to experience different technologies during the preselection phase of the fitting process.