QUANTIFICATION OF THE RELATIONSHIP BETWEEN HEARING AID OUTPUT AND SOUND LEAKAGE FROM THE EAR CANAL
Abstract
This investigation was designed to quantify the relationship between the peak output characteristics of in-the-ear (ITE) hearing aids and the respective acoustic sealing properties of the earmold portion of the ITE aid inserted in KEMAR's ear. It was found that a fairly close frequency correspondence between the ITE output peaks and their sound leak peaks was present. However, in only one instance did they align themselves exactly. The importance of this specific frequency alignment may have significant implications for current experimental and clinical methods being employed to minimize acoustic feedback. Current methods being used to reduce feedback are based on the premise that the feedback frequency is directly related to the frequency of the output peaks. Results of this study do not support this notion entirely. It was found that the fitting or seating of the ITE shell earmold within the ear canal was the factor which contributed the most to sound leakage, and hence, presumably acoustic feedback. The presence of a vent further added to the levels of sound leakage, but to a lesser extent than the actual acoustic sealing properties of the earmold portion of the aid. It was observed that the length of the canal portion of the aid (earmold) is an important consideration when attempting to control acoustic feedback. The longer the canal portion of the aid/mold, the greater the overall SPL delivered to the tympanic membrane, and consequently, the higher the levels of sound leakage from the ear canal. It was observed that an overall reduction in the aids' output levels resulted in a linear reduction for the entire frequency response of the sound leakage curves. Finally, it was concluded that providing a flat insertion gain to maximize output and minimize sound leakage was most effective only when a close frequency alignment existed between the ITE output peaks and their corresponding sound leak peaks. Thus, it was possible to limit the aids' output by reducing the peak output frequency with only a negligible effect on the sound leak peak. Recommendations for future research are given based on the findings of this study.
Degree
Ph.D.
Subject Area
Audiology
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