Hearing Aids Book

	Preface
1	Introductory Concepts	1
1.1	Problems Faced by People with Hearing Impairment	2
1.2	Acoustic Measurements	6
1.3	Types of Hearing Aids	10
1.4	Historical Perspective	12
2	Hearing Aid Components	18
2.1	Block Diagrams	19
2.2	Microphones	21
2.3	Amplifiers	28
2.4	Digital Circuits	34
2.5	Tone Controls and Filters	36
2.6	Receivers	39
2.7	Acoustic Dampers	41
2.8	Telecoils	42
2.9	Audio (Electrical) Input	42
2.10	Remote Controls	43
2.11	Bone Conductors	44
2.12	Batteries	45
3	Hearing Aid Systems	48
3.1	Custom and Modular Construction	48
3.2	Analog Hearing Aids	50
3.3	Digitally Programmable Analog Hearing Aid Systems	51
3.4	Digital Hearing Aids	53
3.5	Remote Sensing and Transmitting Hearing Aid Systems	58
3.6	Induction Loops	59
3.7	Radio-frequency Transmission	64
3.8	Infrared Transmission	69
3.9	Classroom Sound-field Amplification	69
3.10	Strengths and Weaknesses of Remote Transmission Systems	70
3.11	Assistive Listening Devices	72
4	Electroacoustic Performance and Measurement	74
4.1	Measuring Hearing Aids in Couplers and Ear Simulators	75
4.2	Real-Ear Aided Gain (REAG)	89
4.3	Insertion Gain	96
4.4	Practical issues in real-ear testing	101
4.5	Aided Threshold Testing and Functional Gain	106
4.6	Feedback in Hearing Aids	107
4.7	Troubleshooting Faulty Hearing Aids	111
5	Hearing Aid Earmolds, Earshells and Coupling Systems	117
5.1	Earmold and earshell physical styles	120
5.2	Overview of Earmold and Earshell Acoustics	123
5.3	Venting	123
5.4	The Sound Bore: Tubing, Horns and Constriction	137
5.5	Dampers	143
5.6	Specific Tubing, Damping and Venting Configurations	144
5.7	Procedure for Selecting Earmold and Earshell Acoustics	144
5.8	Ear Impressions	146
5.9	Earmolds and Earshells	152
6	Compression Systems in Hearing Aids	159
6.1	Compression's Major Role: Reducing the Signal's Dynamic Range	160
6.2	Basic characteristics of a compressor	161
6.3	Rationales for Use of Compression	169
6.4	Combinations of Compressors in Hearing Aids	180
6.5	Benefits and Disadvantages of Different Compression Systems	181
7	Advanced Signal Processing Schemes	187
7.1	Multi-Microphone and Other Directional Hearing Aids	188
7.2	Single-Microphone Noise Reduction	195
7.3	Feedback Reduction	198
7.4	Frequency Transposition	202
7.5	Speech Cue Enhancement	204
8	Assessing Candidacy for Hearing Aids	209
8.1	The Lower Limit of Aidable Hearing Loss	211
8.2	The Upper Limit of Aidable Hearing Loss	226
8.3	Medically Related Contra-indications to Hearing Aid Fitting	233
9	Prescribing Hearing Aid Performance	234
9.1	General Concepts Behind Prescription and a Brief History	235
9.2	Gain and Frequency Response Prescription for Linear Amplification	238
9.3	Gain, Frequency Response, and Input-Output Functions for Nonlinear Amplification	249
9.4	Allowing for Conductive and Mixed Hearing Losses	262
9.5	Selecting Options for Multi-memory Hearing Aids	264
9.6	Prescribing OSPL90	267
9.7	Excessive Amplification and Subsequent Hearing Loss	276
10	Selecting and Adjusting Hearing Aids	281
10.1	Selecting Hearing Aid Style: CIC, ITC, ITE, BTE, Spectacle Aid, or Body Aid	282
10.2	Selecting Hearing Aid Features	284
10.3	Selecting a Signal Processing Scheme and Prescription Method	286
10.4	Overview of Hearing Aid Selection and Adjustment	289
10.5	Twelve Steps for Selecting and Adjusting Programmable Hearing Aids	290
10.6	Eleven Steps for Selecting and Adjusting Non-programmable Aids	293
10.7	Allowing for Individual Ear Size and Shape in the Coupler Prescription	297
10.8	Allowing for Surgically Altered Ear Canals	300
10.9	Verifying and Achieving the Prescribed Real-ear Response	300
10.10	Verifying and Fine-tuning OSPL90	300
11	Problem Solving and Fine-Tuning of Hearing Aids	302
11.1	Solving Common Problems	303
11.2	Systematic Fine-tuning Procedures	312
11.3	Concluding Comments: Fine-tuning in Perspective	320
12	Counseling the New Hearing Aid Wearer	322
12.1	Understanding Hearing Loss	323
12.2	Acquiring a Hearing Aid	325
12.3	Using Hearing Aids	327
12.4	Adjusting a New Experiences with Sound and Hearing Aids	327
12.5	Care of Hearing Aids	331
12.6	Hearing Strategies	332
12.7	Involving Families and Friends	337
12.8	Communication Training	338
12.9	Avoiding Hearing Aid-Induced Hearing Loss	339
12.10	Assistive Listening Devices	340
12.11	Ongoing Support	340
12.12	Counseling Styles	340
12.13	Structuring Appointments	342
13	Assessing the Outcomes of Hearing Rehabilitation	349
13.1	Speech Identification Testing	351
13.2	Self-report Questionnaires for Assessing Benefit	353
13.3	Meeting Needs and Goals	359
13.4	Assessing Usage, Problems, and Satisfaction	363
13.5	Changes in Outcomes with Time after Fitting	366
13.6	Impact of Hearing Aids on General Health and Quality of Life	368
14	Binaural and Bilateral Considerations in Hearing Aid Fitting	370
14.1	Binaural Effects in Localization	372
14.2	Binaural Effects in Detection and Recognition	376
14.3	Advantages of Bilateral Fittings	380
14.4	Disadvantages of Bilateral Fittings	388
14.5	Tests of Bilateral Advantage	390
14.6	Fitting Asymmetrical Hearing Losses	395
14.7	Deciding on Bilateral versus Unilateral Fittings	399
14.8	Effect of Bilateral vs Unilateral Fitting on Electroacoustic Prescriptions	402
15	Special Hearing Aid Issues for Children	404
15.1	Sensory Experience and Deprivation	405
15.2	Assessment of Hearing Loss	406
15.3	Hearing Aid and Earmold Features and Styles	408
15.4	Prescribing Amplification for Children	412
15.5	Verifying Real-ear Performance	419
15.6	Evaluating Aided Performance	419
15.7	Helping Parents	425
15.8	Hearing Habilitation Goals	428
15.9	Teenagers and Cosmetic Concerns	431
15.10	Safety Issues	431
16	CROS, Bone-Conduction, and Implanted Hearing Aids	434
16.1	CROS Hearing Aids	434
16.2	Bone-conduction Hearing Aids	442
16.3	Implanted and Semi-implanted Hearing Aids	447
	References	451
	Index	487