ELECTROACOUSTIC PERFORMANCE AND MEASUREMENT

4.1 MEASURING HEARING AIDS IN COUPLERS AND EAR SIMULATORS

4.1.1 Couplers and ear simulators

4.1.2 Test boxes

4.1.3 Measurement signals

4.1.4 Gain-frequency response and SSPL-frequency response

4.1.5 Input-output functions

4.1.6 Distortion

4.1.7 Internal noise

4.1.8 Magnetic response

4.1.9 ANSI and IEC standards

4.2 REAL-EAR-TO-COUPLER DIFFERENCE (RECD)

4.2.1 Factors affecting RECD

4.2.2 Measurement of RECD

4.2.3 RECD and REDD

4.3 REAL-EAR AIDED GAIN (REAG) and REAL-EAR AIDED RESPONSE (REAR)

4.3.1 Positioning the probe for REAG measurement
4.3.2 Relationship between REAG, coupler gain and ear simulator gain
4.3.3 Detecting incorrect aided measurements

4.4 INSERTION GAIN

4.4.1 Positioning the probe for insertion gain measurement
4.4.2 Relationship between insertion gain, coupler gain and ear simulator gain
4.4.3 Detecting incorrect insertion gain measurements
4.4.4 Accuracy of insertion gain measurements

4.5 PRACTICAL ISSUES IN REAL-EAR TESTING

4.5.1 Probe calibration
4.5.2 Control microphones
4.5.3 Effects of wax
4.5.4 Contamination by background noise
4.5.5 Hearing aid saturation
4.5.6 Loudspeaker orientation
4.5.7 Measurement signal characteristics

4.6 AIDED THRESHOLD TESTING AND FUNCTIONAL GAIN

4.7 FEEDBACK IN HEARING AIDS

4.7.1 The feedback mechanism
4.7.2 Effects of feedback on sound quality
4.7.3 Probe-tube measurements and feedback

4.8 TROUBLESHOOTING FAULTY HEARING AIDS

4.9 CONCLUDING COMMENTS