Customized acoustic transform functions and their accuracy at predicting real-ear hearing aid performance

Objective: The purpose of the study was to evaluate the validity of predict ing the real-ear aided response by adding customized acoustic transform fun ctions to the performance of a hearing aid in a 2-cc coupler. Design: The real-ear hearing aid response, the real-ear-to-coupler differen ce (RECD/HA2), and field to behind-the-ear microphone transfer functions we re measured in both ears of 24 normally hearing subjects using probe-tube m icrophone equipment. The RECD/HA2 transform function was obtained using bot h insert earphones and with the hearing aid! pressure comparison method. An RECD/HA2 transfer function was also obtained with a customized earmold, ER -3A foam tip, and an oto-admittance tip. Results: Validity estimates were calculated as the difference between the d erived and measured real-ear response. The derived response was generally w ithin 5 dB of the measured real-ear response when it incorporated an RECD/H A2 transform function obtained with a customized earmold for the specific e ar in question. Discrepancies increased when the RECD/HA2 transfer function was obtained from the same subject but the opposite ear. There were signif icant differences between the RECD/HA2 transform function obtained with cus tomized and temporary earmolds, As a result, the derived response incorpora ting these transforms differed significantly from the measured real-ear res ponse obtained with the customized earmold. The insert earphone and the hea ring aid RECD/HA2 transfer function were equally valid. Conclusions: The derived response may be used as a substitute for in situ h earing aid response procedures when it incorporates acoustic transform func tions obtained with a customized earmold from the specific ear in question.