Acoustic differential digital coder

A digital speech communication system comprising

• a closed chamber having at least first and second apertures therein;
• a vibratory diaphragm with its periphery secured to the periphery of said first aperture;
• means for applying a speech wave to said vibratory diaphragm from outside said closed chamber;
• means responsive to the motion of said vibratory diaphragm for producing a quantized signal representative of said diaphragm motion;
• means responsive to said quantized signal for producing a coded digital signal;
• means covering said second aperture for converting said coded digital signals into sound waves and for radiating said sound waves into said chamber to modify the motion of said diaphragm, said coded digital signal producing means producing a differential coded digital signal corresponding to said speech wave.

Apparatus for converting coded digital signals into sound comprising

• a cylindrical electret,
• at least one insulative cylindrical wall, the first insulative cylindrical wall being concentric with and surrounding the cylindrical electret,
• at least one ring electret, the first ring electret being concentric with and surrounding the first insulative cylindrical wall, the successive ring electrets each being concentric with and surrounding one of the insulative cylindrical walls,
• said electrets and insulative walls forming an assembly having a sound emitting end with each electret being acoustically isolated from the other electrets,
• means for selectively applying coded digital signal elements to said acoustically isolated electrets,
• a first cavity extending from said sound emitting end adapted to acoustically sum sound waves from the acoustically isolated electrets,
• and a second cavity extending from said first cavity adapted to restrict the frequency range of the summed sound waves.

Apparatus for converting coded digital signals into sound comprising:

• a cylindrical electret,
• a first insulative cylindrical wall concentric with and surrounding the cylindrical electret,
• a first ring electret concentric with and surrounding the first insulative cylindrical wall, the area of the first ring electret being one-half the area of the cylindrical electret,
• a second insulative cylindrical wall concentric with and surrounding the first ring electret,
• a second ring electret concentric with and surrounding the second insulative wall, the area of the second ring electret being one-half the area of the first ring electret,
• said electrets and insulative walls forming an assembly having a sound emitting end with each electret being acoustically isolated from the other electrets,
• a cylindrical cavity contiguous to said sound emitting end adapted to acoustically sum sound waves from the acoustically isolated electrets, and
• an acoustical filter adjacent to the sound wave summing cavity adapted to remove frequency components of the summed sound waves above the sampling frequency of the digital signals.