What technology made telephones possible?

Answer 1

Like most modern inventions, the telephone owes its inception to a combination of scientific theories, technology, and imagination. This answer deals with technologies used on the telephone that were not used in its predecessor, the telegraph. Also, we will avoid discussing the switching network that makes a telephone ring just one other telephone and not all telephones everywhere at the same time.

The foremost technology for the telephone was the invention of a practical microphone which could convert sound waves into electrical signals. The first telephones contained a microphone that used carbon powder behind a thinly stretched pliable material. The carbon powder had an electrical field running through it and the pressure from sound would compress the carbon and increase its electrical conductivity. The carbon granules had to compress and decompress several thousand times a second to reproduce a distinguishable human voice.

Another pivotal concept wasn't so much a technology as the modern foundations of electrical engineering. Maxwell's Laws, which are a cornerstone in any modern electrical appliance, were still under discussion at the time of Alexander Graham Bell's famous invention. These four equations (and the dozens of implications these laws entail) provided the framework for many of the circuits essential to a practical telephone.

Modern telephones use a technological spectrum as vast as what you find in a personal computer. They employ semiconductors, digital signal processing, modems (used for caller-id), analog filters, acoustics, and static mechanics to deliver cheap and reliable voice communication.