1 янв 1920 г. - 1900-the 1920s: The Telephone Age

Описание:

Electric hearings aids came into play at the beginning of the 20th century, with the advent of the carbon microphone. While based on the telephone principle, Alexander Graham Bell was not involved in their development. The carbon microphone reproduced sound by using sound waves to compress carbon against a diaphragm. As such, these carbon models were ineffective for serious hearing loss.