Hearing aids: design, mechanics, and characteristics.
D000162:Acoustics / Q000295:instrumentation; D000669:Amplifiers, Electronic; D004431:Ear, External; D011211:Electric Power Supplies; D004582:Electronics, Medical / Q000295:instrumentation; D006310:Hearing Aids / Q000145:classification / Q000266:history; D034381:Hearing Loss / Q000628:therapy; D049672:History, 19th Century; D049673:History, 20th Century; D049690:History, Ancient; D006801:Humans; D007878:Legislation as Topic; D013016:Sound; D014481:United States