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Examen
ILE Exam Hearing Aids 2023
Hand Cupped Behind Ear - -first Hearing Aid 
-increased sound by 5-8db 
-included horns,trumpets, speaking tubes 
 
1892 - -carbon amplifiers patent by Alexander Bell 
-marketed 1902-1903 until 1930;first patent for a telephone type hearing instrument 
 
1920 - large vacuum tubes; not portable 
 
1938 - miniature vacuum tube ;crystal receivers 
 
1930 - diameter reduced 
 
1940 - bone conduction receivers were introduced 
 
1946 - first telecoil introduced 
 
1950 - bodyworn HA became convenient...