Speaker Phones Are Phones

• Above their speaker capabilities, speaker phones are actual telephones. They receive a caller's voice in a small microphone which converts the airborne vibrations of sound into electrical signals for transmission across a connected telephone two-wire circuit. The phone also receives electrical impulses generated by the other party's telephone, and converts those signals back into sound using a small, high-quality speaker. Additional features, such as digital displays, are controlled by electronic circuit boards within the phone housing.
  
  

Some Speaker Phones are One-Way

• Some speaker phones, especially older or low-quality ones, use a one-person-at-a-time voice transmission method known as "half duplex." In a half duplex setup, the device disables the built-in microphone when the speaker is playing incoming sounds; in this configuration, the microphone must be disabled so that sounds from the speaker are not picked up and sent back to the party on the other end. If the microphone were not disabled, the both parties would hear a feedback or echo sound every time the party on the other end spoke. Half-duplex speaker phones were common in the 1980s and early 1990s, and are still widely available on inexpensive phones, but are not preferable because the configuration allows only one party at a time to speak and be heard.
  
  

Full-Duplex Speaker Phone Work Both Ways

• In the 1990s, new technology allowed speaker phones to begin operating in full-duplex mode, a feature that allowed parties on both ends to speak at the same time and still be heard. Full-duplex speaker phones work by digitizing the incoming sounds from the other party, or parties, on the line; when the sounds are played over the speaker and picked up by the microphone, proprietary software in the phone electronically removes the sounds picked up from the speaker. The modified sound is then converted into electrical signals and sent out over the telephone line. Since full-duplex speaker phones remove the sounds generated by the phone's own speaker, there is no need to disable the microphone; as a result, both parties are able to speak at the same time without being cut out by the phone's function.