The Vacuum Tube Age of Hearing Aids (1 янв 1920 г. – 1 янв 1949 г.)
Описание:
Earl C. Hanson invented the vacuum tube hearing aid and named it the vactuphone. Was one of the first hearing aids that a person could wear around the ear. Technology for amplification was better than previous hearing aids, though this hearing aid required two batteries making the cost greater.Добавлено на ленту времени:
Дата:
1 янв 1920 г.
1 янв 1949 г.
~ 29 years