Ericsson's bakelite telephone, which was launched in 1931, was primarily known for its trend-setting design, but it also contained an important technical innovation called anti-side tone coupling. Previously, the speech signal, as well as background noise, picked up by the microphone could also affect the receiver. Now, for the first time, a differentially coupled speech transformer was used that reduced interference from the microphone, resulting in a significant improvement in speech quality. In addition, the dial, the microphone and the earpiece were of a new design.
The bakelite telephone was produced in several models, one of which was an intermediate phone with an extension. Two telephones could be connected to the same line, and with the push of a button, either could be used for external calls. Calls could also be made between the two telephones.
The bakelite phone was also produced as an extension phone, which had a smaller case, since it did not include a bell. The extension phone was very popular in offices, two-story homes and bedrooms, where people did not want to be disturbed when the telephone rang but still wanted to be able to make calls.
Despite the continuing automation of the telephone network, telephones with local batteries were still required. Such phones were also produced in bakelite according to the new design. These phones had no dial but instead had a crank and a signal inductor.
A new bakelite telephone with smoother contours and improved transmission characteristics was introduced in 1947. On the new model, the outer ring of the dial was also made of bakelite, which created a better overall impression. The model with a handheld microphone had also been given a smoother design. Both the microphone and the earpiece were newly designed, with improved sound reproduction and a more sensitive receiver.
Author: K V Tahvanainen