The research paper in 1925 by Chester W. Rice and Edward W. Kellogg at General Electric was important in establishing the basic principle of the direct-radiator loudspeaker with a small coil-driven mass-controlled diaphragm in a baffle with a broad midfrequency range of uniform response. Edward Wente at Bell Labs had independently discovered this same principle, filed patent No. 1,812,389 Apr. 1, 1925, granted June 30, 1931. The Rice-Kellogg paper also published an amplifier design that was important in boosting the power transmitted to loudspeakers. In 1926, RCA used this design in the Radiola line of a.c. powered radios.
Figures illustrating a large free-edged paper cone, coil driven, conical diaphragm loudspeaker unit. According to Rice-Kellogg, "the conclusion from these experiments was to the effect that the best practical solution of the loud speaker problem was a device combining the following features: a conical diaphragm four inches or more in diameter with a baffle of the order of two feet square to prevent circulation and so supported and actuated that at its fundamental mode of vibration the diaphragm moves as a whole at a frequency preferably well below 100 cycles."
According to Rice-Kellogg, "voices and music do not sound natural unless reproduced at approximately the original level of intensity, even though the reproduction may be free from all wave form distortion. In order, therefore, that the full benefit of a high grade loud speaker may be realized, it is important that the amplifier which goes with it should have sufficient capacity to give a natural volume or intensity." The figures above "are views of a laboratory model of a cabinet set containing rectifier, amplifier, and loud speaker. The front of the cabinet acts as baffle. To prevent air rsonance in the box, the sides and back are vented by inserting panels of perforated brass." (p. 474)
Sources:
Rice, Chester W. and Edward W. Kellogg, "Notes on the Development of a New Type of Hornless Loudspeaker," Transactions of the American Institute of Electrical Engineers 44, 1925, p. 461-475
