Telephone Early Commercial (technically diverse)

Early telephones were technically diverse. Some used liquid transmitters which soon went out of use. Some were dynamic: their diaphragms vibrated a coil of wire in the field of a permanent magnet or vice versa. Such sound-powered telephones survived in small numbers through the 20th century in military and maritime applications where the ability to create its own electrical power was crucial. Most, however, used Edison/Berliner carbon transmitters, which were much louder than the other kinds, even though they required induction coils, actually acting as impedance matching transformers to make it compatible to the line impedance. The Edison patents kept the Bell monopoly viable into the 20th century, by which time telephone networks were more important than the instrument.